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Special Paper 32

A SUMMARY OF SPECIAL PAPER 31:MITIGATING GEOLOGIC HAZARDS IN OREGON:

A TECHNICAL REFERENCE MANUAL

By

John D. Beaulieu and Dennis Olmstead

Oregon Department of Geology and Mineral Industries

1999

Geologic Hazards:Reducing Oregon’s Losses

Oregon Department of Geology and Mineral Industries Special Papers, ISSN 0278–3703

Published in conformance with ORS 516.030

This publication is a summary of the Oregon Department of Geology and MineralIndustries’ Special Paper 31: Mitigating geologic hazards in Oregon:A technical refer-ence manual, which contains more complete information about natural hazards inOregon and how to mitigate them.

For copies of these publications or other information about Oregon’s geology andnatural resources, contact:

Nature of the Northwest Information Center800 NE Oregon Street #5Portland, Oregon 97232

(503) 872-2750http://www.naturenw.org

SPECIAL PAPER 32

Geologic Hazards:Reducing Oregon’s Losses

by

John D. Beaulieu, State Geologistand

Dennis L. Olmstead, Deputy State Geologist

Oregon Department of Geology and Mineral Industries

1999

STATE OF OREGONDEPARTMENT OF GEOLOGY AND MINERAL INDUSTRIES

John D. Beaulieu, State Geologist

Table of contents

Executive summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

Why a technical reference manual? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

Recognize that geologic hazards are a growing problem . . . . . . . . . . . . . . . . . . . . . .3

Properly characterize the geologic hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

Create an equitable team of stakeholders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Know the specific reason for the strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Strategies are community specific . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Select from a range of strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Make the strategy permanent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Proceed with perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

Appendix 1: The diversity of geologic hazards in Oregon . . . . . . . . . . . . . . . . . . . . . .7

Appendix 2: Selected geologic disaster events in Oregon . . . . . . . . . . . . . . . . . . . . . .8

Appendix 3: Damage from geologic hazards in Oregon . . . . . . . . . . . . . . . . . . . . . . .9

Appendix 4: Specific hazard characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

Appendix 5: Multi-hazard relationships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

Appendix 6: Geologic hazard risk reduction by state and local agencies . . . . . . . .14

Appendix 7: Range of strategies to reduce risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

Appendix 8: Concluding questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

Floods are one of Oregon’s most common natural disasters, affecting homes, businesses, farms, roadsand railroads.

Special Paper 32—Geologic Hazards: Reducing Oregon’s Losses 1

Executive summaryThe science of geology tells us that natural disas-ters of the future will exceed those that we haveexperienced in our brief written history.Oregon has a variety of geologic hazards includ-ing landslides, debris flows, floods, earthquakes,volcanoes, tsunamis, and erosion. The risks posed by these hazards can be man-aged so that the benefits achieved are acceptablein terms of costs. The keys to managing the riskare having enough information about the hazardand taking the proper steps in risk reduction. Reducing risks from geologic hazards involvesseveral steps. These are: • Properly characterizing the hazard;• Building a team to develop strategies;• Considering a range of strategies to address

the risk;• Choosing the appropriate strategies from a

broad range of choices;• Permanent integration of the strategies to

assure ongoing success.Community efforts that do not include each ofthese steps may not be fully effective. There maybe adequate information about a hazard, butunacceptable strategies are proposed.Alternatively, strategies may be acceptable, butmay not be effective, because the hazard was notfully understood. Other reasons why strategiesmay be ineffective are:• Strategies may develop good information

about hazards butdo not link to riskreduction actions.

• Strategies mayinclude actionsreducing risk butnot adequatelycharacterize thehazards.

• Strategies mayplace the burdenfully on local government without benefit oftechnology transfer or proper technical infor-mation from sources better able to providescientific and technical information.

• Strategies may place the emphasis on interac-tion and process but not on understandingthe hazard or finding the most effective riskreduction methods.

In Oregon, there are many opportunities toreduce risks from geologic hazards. Land usestatutes and goals, building code regulations,construction practice manuals, public education,and voluntary actions have equally importantroles in risk reduction.

Processes for imple-menting risk reduc-tion may include ruledevelopment, com-prehensive plans,periodic review ofplans, ordinancedevelopment, publiceducation, or otherstrategies by a vari-ety of agencies.

The focus of this manual is to present the haz-ards and insights and information on how theycan best be understood and managed from atechnical and a risk-management point of view.It includes basic elements that should be presentin any effective regulatory or decision makingprocess.

Landslides are a common problem throughoutOregon. This 1996 landslide in Portland’s WestHills directly affected at least four lots and tworoads. The major damage occurred to the houselocated across the street from the slide.

A firm basis for action includes:• Characterizing the hazard• Using a carefully selected team • Considering a range of strategies• Selecting the best strategy• Institutionalizing the strategy

2 Special Paper 32—Geologic Hazards: Reducing Oregon’s Losses

Why a technical reference manual?Oregon has among the widest variety of signifi-cant geologic hazards of any state in the union.

Demographics are increasing therisk of natural hazards to Orego-nians as development is increas-ingly being carried out on morehazardous land than in the past.With proper information, it is pos-sible to manage the risks posed bythese geologic hazards.

In spite of efforts to manage risks,some actions are ineffective atreducing damage from geologichazards. There are many reasons,including: • The hazards are unrecognized

or poorly understood;• The full range of choices for

risk reduction is not fullyappreciated;

• The issue is so diverse andinvolves so many participantsthat the process simply bogsdown and dies out;

• The community chooses tohandle the hazard on a case-by-case basis rather thandevelop a comprehensivestrategy;

• Legal jeopardy may not bewell understood.

It is common for those who findthemselves dealing with hazardsto enter into the arena with:

• Incomplete knowledge of theirtask;

• Lack of understanding of all thehazards they need to consider;

• Lack of awareness of all the choices that existand the tradeoffs associated with each;

• Lack of awareness of the total geographicarea in need of policy.

It is important to point out that risk reductionstrategies may not totally eliminate the hazard,but rather may be better viewed as attempts toeffectively manage the risk.

Among other information, the appendices to thismanual summarize the geologic hazards ofOregon, provide perspectives on how the geo-logic view of the hazard may differ from the

view provided by history alone, and list severalgeneral strategies that might be pursued in thereduction of risk from hazards.

This manual is a summary of “A summary ofrisk reduction of geologic hazards: A technicalreference manual for Oregon (Special Paper 31).”See that publication for more information oneach section of this manual.

The effects of flooding do not end when the water recedes.Cleanup and rebuilding may take months; in some cases, struc-tures, properties, or even neighborhoods must be abandoned.Flood control measures must be carefully planned so they donot cause more problems downstream.


Recognize that geologic hazardsare a growing problemReduction of risk from geologic hazards is ofincreasing concern to communities in Oregon fora variety of reasons. • Oregon is a state with a wide range of geo-

logic hazards with significant impacts. • Demographics are pushing development into

higher hazard types of terrain. • Recent legal actions are better defining the

responsibilities and liabilities of communities,developers, and landowners.

• Regardless of the overall average risk for thestate, the specific site where a disaster occursis catastrophic for the victims, so reasonablesteps to manage the risk are expected.

If the community does too little to manage risk,unnecessary losses will occur; if they do too much tocontrol risk they may invite legal actions based onthe “takings” doctrine. The challenge is to forge astrategy that optimizes the benefits of effective gov-ernance while minimizing the negatives. Key com-ponents are risk reduction, avoidance or manage-ment of liability issues, and sensitivity to cost issues.

Properly characterize the hazardsFor a geologic hazard to be properly mitigatedthe hazard first must be characterized. This

involves a determination of what the hazard is,where the hazard is, how bad it is, and howoften it might become a problem.

Delineation (where the hazard is) is just part ofcharacterization. There may also be a need toevaluate the interplay of the specific hazardagainst other hazards. Sometimes a proposedsolution for one hazard simply aggravates anoth-er hazard. Multi-hazard analysis is recommend-ed where more than one hazard exists.

In states like Oregon we deal with many kinds ofgeologic hazards, including landslides, debrisflows, floods, earthquake ground response, vol-canic hazards, tsunamis, and erosion. For each ofthese hazards, our historic record of losses onlytells part of the story, given the shortness of therecord. Available information on hazards certain-ly should be consulted, but in many instances,available information alone may not be adequate.

Proper characterization of the hazard enables usto understand the extent, magnitude, frequency,and causes of the hazard in a manner adequateto develop and implement risk managementstrategies. Where hazards are found to be mini-mal, the community might be better served toplace its energies elsewhere. Where hazards aresignificant, carefully selected strategies of riskreduction are in order.

Ground response maps are one tool to characterize earthquakes. The maps show how the ground willrespond to earthquakes in terms of amplification, liquefaction, and landslides. These maps, like theone above for Astoria-Warrenton, must be used in conjunction with bedrock shaking maps and a riskassessment before a community can completely understand its risk.


Create a team of stakeholdersRisk reduction is the interest of a wide range ofstakeholders. A properly selected team of partici-pants must be constructed to address the risk.For small and simple hazards, the team of stake-holders may be small, strategic, even informal.For large and difficult hazards, more formal andlarger arrangements are advised, with a largerarray of stakeholders.In large and difficult hazard situations, riskreduction can be the responsibility of the Build-ing Codes official, planner, public, roads depart-ment, property owners, realtors, emergencymanagement system, and others. Actions takenby each can help to manage the risk, though noone party by itself manages all the possible risks. In areas of lesser hazard, the team may be muchsmaller, limited to a few key persons. Publicinterest and participation will vary with publicknowledge of the hazard and with the potentialimpacts of the hazard. The role of the scientist and engineer is to pro-vide expertise so that considered options are alsofeasible. However, science provides means tocharacterize the hazard but does not dictate thefinal policy choices.Project Impact, a new national initiative spon-sored by the Federal Emergency Management

Agency (FEMA), is one ofmany efforts that can beused at the local level tobring together citizens, gov-ernment, and the privatesector to minimize lossesbefore the next disasteroccurs. Partnering efforts,regardless of scale, can be asuccessful means of riskreduction.

Know the specificreason for the strategyStrategies to address geo-logic hazards can be manyand varied. Because strate-gies inevitably involvetradeoffs, it is important toclearly define the reason forthe strategy or policy beforedecisions are made.

For example, a hazard line for coastal erosiondesigned for possible future insurance purposesmay not be the line desired by planners who aretrying to avoid all losses. A key element then, to the development ofhazard risk reduction policy, is a clear recogni-tion of the desired outcome of the policy.These outcomes should be itemized, so thesuccess of the policy can be measured afterimplementation.

Strategies are community specific

Selecting risk management strategies involvesbalancing of the amount of risk, the benefits andthe liabilities of each possible action, and the val-ues of the community. Given the variability ofconditions, community values, economic consid-erations, and other factors, it is clear that strate-gies need to be developed locally, based on aclear characterization of the local hazard.

The emphasis should be on making decisionsthat are tailored to a jurisdiction rather thanadopting preexisting language from anotherlocation, or from a “model ordinance.” At thesame time, reviewing a well-developed ordi-nance from an analogous area can provide agood starting point in the development of a com-munity-specific regulation or ordinance.

Many structures were built before our current understanding of coastalprocesses. Efforts to stop erosion can be costly and may trigger unex-pected behavior on adjacent coastline property.


Select from a range of strategies Knowing the full range of available mitigationactions is helpful when choosing acceptablestrategies.

Equally as important as characterizing the haz-ard is the decision process by which a communi-ty decides to deal with the hazard. For a givenhazard, there are many paths to risk reduction.In general, strategies may include but are notlimited to

• Simple or complex ordinances (zoning, subdi-vision, development codes);

• Building code provisions;

• Continuing public education efforts;

• Incentives or disincentives, such as tax credits;

• Revised construction and design manuals forlifelines; and

• Coordinating efforts when jurisdictions abutone another in a hazard zone.

The selection of effective local strategies dependson the nature and the degree of the hazard. Itdepends on the needs and wants of the commu-nity and on the desired or acceptable level ofinvestment that might apply to the solution. Italso depends on the level of risk and the level ofregulation or restraint on property use that thecommunity is willing to accept.

These discussions can take place locally, region-ally, or at the state level, depending on jurisdic-tion. The Oregon Department of Geology andMineral Industries has responsibility to provideinformation on geologic hazards.

Particularly in a state like Oregon, where haz-ards are so varied and pervasive, it is importantto understand that the potential solutions to theproblems posed by the hazards are as varied asthe hazards and the communities themselves.

Make the strategy permanent

The selected risk reduction strategy must be putinto place permanently, so that the effort contin-ues after those who were initially involved areno longer available for implementation. This iscalled institutionalizing the strategy.

This may include adoption of

• Planning ordinances;

• Building code revisions;

• Training efforts;

• Public information strategies including publi-cations or signs;

• Programs on storm water management anderosion control;

• Emergency plan chapters;

• Revising construction and design manuals;

• Revising manuals for road construction; and

• Education projects directed toward increasingpublic awareness of the hazard.

Depending on the strategy adopted, the leadresponsibility for reducing the risk may fall toa planner, a building code regulator, an emer-gency manager, a scientist, a member of theprivate sector, or some other member of therisk reduction team.

Coastal communities are preparing their resi-dents and tourists for the next inevitable tsuna-mi. A variety of methods are being used, fromgeneral information about tsunamis to detailedevacutation routes, including this sign in Rock-away Beach, Tillamook County.


Proceed with perspectiveA firm basis for action includes hazard character-ization, team effort, consideration of a range ofstrategies, selection of the best strategies, andcareful selection of the method of institutionaliz-ing policy through implementation.

A jurisdiction may be willing to proceed towardthe formulation of strategies, but the informationbase or the resource base may not be adequate tojustify moving ahead.

A minimal effort of risk reduction from geologichazards should

• Properly characterize the hazards;

• Address multi-hazard issues;

• Involve a team of stakeholders, including thepublic;

• Address an array of choices for risk reduction;

• Select a choice and make the choice perma-nent; and

• Demonstrate a reasonable chance of successbased on scientific principles.

This array of defined steps collectively removesmany of the uncertainties that poorly thought-out efforts bring with them. For hazard situa-tions of limited impact, scaled-down efforts arejustified, but the key components should still beconsidered.

Using this process can optimize the prospects ofproperly managing the hazard and minimize thechance of pursuing ineffective strategies. It canengage stakeholders and educate the public.Further, the rigor, balance, and objectiveness ofthe process can minimize exposure to future law-

suits arising from perceived arbi-trariness or unacceptable work.

Finally, as communities developand deal with geologic hazards,they generally discover that simpleand general strategies may work atfirst, but more focused efforts thataddress specific local conditionsand issues work better throughtime. This is particularly truewhere communities expand intonew areas with greater hazardpotential. Development oftenintensifies through time in a givenarea, leading to increased hazardpotential as a result of alterationsto the natural terrain.

Where a city and a county or twocities abut one another and share acommon hazard situation, theymay wish to cooperate in a broadstrategy of risk reduction.

Few buildings completely collapse in an earthquake. Cost-effec-tive mitigation activities can focus on well-understood potentialproblems. For example, an important stress point is where twobuildings of different heights intersect. Photo courtesy ofNational Geophysical Data Center.

Though volcanic eruptions are the most spectac-ular geologic hazard, there is typically plenty ofwarning and well-defined danger zones forOregon’s volcanoes. Photo courtesy of NationalGeophysical Data Center.


Appendix 1. The diversity ofgeologic hazards in Oregon

Oregon displays great vari-ety of geologic settings, geo-logic hazards, types of devel-opment, and potential lossesfrom geologic hazards.Efforts at geologic hazardrisk reduction in the statevary depending on setting,cause, rock type, generalgeology, current land usepractices, future land use,and numerous other factors.

• Earthquakes are generat-ed from three locations:the shallow crust, theCascadia subductionzone fault off the coast of Oregon, and thesubducting slab under the crust. Predictedlosses in the future for Oregon indicate hun-dreds or thousands of lives lost on the aver-age every 500 years and $65 million damageas an annualized average.

• Landslides are generally related to variouscombinations of slope, rock, type, and cli-mate. In general, moderate-slope slumps andsteep-slope debris torrents dominate recentdiscussions. Losses for Oregon generallyaverage less than one or two lives per yearand $1 million to $10 million per year.

• Coastal erosion generally averages a fewinches per year, but may be up to severalhundred feet in one year in sandy areas.Rates vary elsewhere for certain kinds of highslope settings and other specialized situa-tions. Major causes are sea level rise, cyclicclimatic activity, and unstable landforms.Progressive losses over the years havedestroyed all or parts of many communitiesand roads along the Oregon Coast.

• Volcanic hazards are infrequent but can beextreme in their consequences. In Oregon, ashfall, localized lava flows, and extensive debrisflows down major river channels are the mostlikely threats.

• Tsunamis are large waves caused by under-sea earthquakes or landslides. Oregon isthreatened both by tsunamis from distantsources and tsunamis generated by activityon the Cascadia subduction zone. Deathsfrom a large tsunami along the Oregon coastcould easily be in the range of 5,000 duringtimes of high beach use, if proper publiceducation has not been effectively institu-tionalized.

• Flooding in Oregon includes lowland floodingof major stream valleys and torrential floodsdown more restricted valley channels cut intothe mountains. Deaths are rare, but in oneevent, Oregon experienced the third-largestfatality total of any flood in the nation since1900. Economic losses have topped hundredsof millions of dollars in some recent floods.

• Stream bank erosion is a hazard which hasgained more prominence as fish survival hasbecome a higher priority for the state. Otherissues include stability of construction inareas of severe erosion, long-term migrationof channels, and land use. Major stream bankerosion occurs where major streams leavemountainous areas and pass through transi-tion reaches where sediment loads are highlyvariable relative to the capacity of the streamto move them.

High rainfall and saturated ground contributes to floods, landslides,erosion, and increased earthquake damage. Road closures due to land-slides are common in the winter in many places in Oregon.

Appendix 2. Selected geologic disaster events in Oregon

EVENT FREQUENCY GEOLOGIC CAUSES AND DESCRIPTION

"100-YEAR" More than 5 • Geology and slope inhibit upland infiltrationFLOODS IN since 1970 • Channels convey water very rapidlyTILLAMOOK • Gravel modifies stream cross sections

• Numerous rivers enter the valley

LARGE FLOOD >100 years • Unusual geologic channel produces unusual flood potentialAT LAKE • Headwater dam was insufficient for large flood eventsOSWEGO, 1996 • Construction occupies ancient flood plain

• Rain-on-snow weather pattern

DISASTROUS 50–100 years • Unique geology dictates disastrous debris flows keyed toDEBRIS FLOWS intense rainfallIN COLUMBIA • Community and lifelines are located on low, flat ground RIVER GORGE constructed by debris flows

FLOOD/DEBRIS 100 years + • Intense storms coupled with minor channels and natural channel TORRENTS debris or culture-related channel debrisIN MINOR • Historic losses of 247 lives at Heppner, 50 lives at Mitchell,DRAINAGES 4 lives near Roseburg in 1996, $10 million in Ashland 1996

LARGE Ongoing • $150 million real estate threatened prior to mitigation in mid-1980sLANDSLIDES until • Geology dictates slip surfaces beneath parts of the cityAT THE DALLES mitigated • Irrigation aggravated slide potential

POTENTIAL 100 years • Distant water supply requires overland pipes across unstableLOSS OF terrainPORTLAND • Pipelines cross active landslides and occupy prehistoric volcanic WATER SUPPLY debris channel from Mount Hood

• Landslide damage to pipe in 1998• Geologic analysis in 1973 spurred construction of a backup

water-supply well field closer to town

COASTAL Ongoing • Rates dictated by geology, type of slide, climate and oceanographyEROSION • Losses include parts of Newport, Bay Ocean, numerous parts of

other communities• Episodic rates very high in sandy terrain (several hundred feet in

some seasons)

FUTURE 100–300 years • Actual risk is greater than that implied by brief historic recordCRUSTAL OR • Construction practice historically lagged behind appropriateINTRASLAB requirements until recentlyEARTHQUAKE • Shift to Zone 3 in western Oregon (1991) addressed requirements

for new construction

SUBDUCTION 300–600 years • Locked subduction zone ruptures in one or several closely spacedZONE events with magnitude range of 8.0-9.0 impacting all of westernEARTHQUAKE Oregon· · • Shift to Zone 3 (1994) and Zone 4 (south coast 1998) addresses

new construction

TSUNAMI AT 300–600 years • Tsunamis from subduction events repeat on Oregon coastSEASIDE • Susceptible to distant tsunamis (from Alaska, 1964)AND OTHER • Communities are located on low-lying groundCOASTAL • Mitigation includes selective building restrictions, evacuationCOMMUNITIES routing, and public education



Appendix 3. Damage from geologic hazards in Oregon

GEOLOGIC PREHISTORIC HISTORIC FUTURE IMPACTS BASED ONHAZARD IMPACTS IMPACTS GEOLOGIC UNDERSTANDING

LANDSLIDE Large scale landslides $150 million in threatened Greater losses in the future inhave formed large real estate at The Dalles in urban or developed areaslandforms and have 1980s; 8 deaths in Douglas owing to demographic trendsblocked numerous rivers County in 1974; 8 deaths in for growth into less stableto form lakes as at Loon several events in Oregon in areas and increasing generalLake, Triangle Lake, and 1996; tens of millions of population pressures on the land.Bonneville. damage per year.

CHRONIc Several miles of coastal Loss of all or parts of Coastal retreat varies from aCOASTAL retreat in many areas in numerous developments few inches per year to a footEROSION past 10,000 years in communities including per year on the average,

coupled with sea level Bay Ocean, Cape Meares, depending on geology andrise. Short term erosion Newport, Lincoln City and oceanography and can beof sandy areas can be others (The Capes). gradual or sporadic with largeextreme. periods of no loss.

FLOOD/ Geologic evidence of a 18 deaths in Vanport Flood Future flooding is inevitableDEBRIS variety of floods of in 1948. Over 50 deaths in as seen recently in Tillamook,TORRENTS variable statistical sizes Mitchell in an event prior to Prineville, etc., but impacts

for all drainages. Debris 1900s and 247 deaths at Hepp- are mitigated by present damtorrents very common in ner on June 14, 1903, from system and by National Floodmuch steep terrain. a debris torrent originating Insurance program.

in Balm Fork Canyon

EARTHQUAKE Large-scale Cascadia A magnitude 5.5 to 6.0 Large scale Cascadiaearthquakes of earthquake in Oregon with earthquakes of magnitude 8.5–9.0magnitude 8.5–9.0 for damage in the tens of for western Oregon withcoastal Oregon with millions of dollars as at additional extensive damageadditional extensive Scotts Mills and Klamath related to tsunami. Risk variesdamage related to Falls in 1993. with ground response andground response and building type.tsunami.

TSUNAMI Numerous coastal 4 deaths from the Alaska Cascadia subduction zonevillages of Native tsunami in 1964 plus tsunamis will yieldAmericans destroyed or considerable damage in considerable damage;impacted as seen in various communities mitigation strategies focusingarcheological record, including Seaside, on critical and essentialinferred from geologic Florence, and Cannon buildings, evacuation, andrecord and heard in Beach. public education.myth record.

VOLCANIC Volcanic activity is, Only a few small events in Varied with major hazard tovaried, widespread and Oregon including minor lifelines and inhabitants ofcontinuing to present day, eruptive activity at Mount key drainage areas such asbut sometimes with Hood in the 1800s and a the Sandy River drainage;prolonged dormancy few deaths there related to events have low frequency ofperiods for any given gas emissions in the Crater occurrence and are generallyvolcano. Numerous native Rock area; Mount St. Helens preceded with precursorsAmerican legends; Old in Washington erupted in adequate to triggerMaid Flat-Sandy River hot 1980 with a large lateral evacuations.mudflow event in 1780s. blast, killing 57 people. (Continued on next page)


Appendix 3. Damage from geologic hazards in Oregon (continued)

GEOLOGIC PREHISTORIC HISTORIC FUTURE IMPACTS BASED ONHAZARD IMPACTS IMPACTS GEOLOGIC UNDERSTANDING

STREAMBANK Strong evidence of large- Much of the historic areas Areas of increasing need forEROSION scale stream migration in of stream-bank erosion attention involve the

flood plains of most major were addressed with levee interplay of residentialstreams, particularly those construction in earlier development, streamof the major streams decades; the shortcomings instability, ecologicalentering valleys from of this approach as a concerns, lifeline stability,mountainous areas. universal strategy are seen and channel modification

in the scattered levees now through dredging or nearbyfar from streams. aggregate mining.

Planning offices should not be viewed as the key lead agency in the reduction of risk for all hazards, or as responsible for thereduction of all risk from geologic hazards. Specifically note that in the above table, lives were lost in landslides in DouglasCounty in circumstances not under the control of a planning office. In the 1996 event at Hubbard Creek, the homes werenot authorized, and no building permits were obtained for them. In the 1974 event, deaths involved repair crews working ininclement weather.


Appendix 4. Specific hazard characterization

GEOLOGICHAZARD CHARACTERIZATION COMMENTS

EARTHQUAKE Bedrock shaking map Shows how much bedrock shakes in the general case; completefor Oregon; undergoing minor adjustments periodically. Usedfor broad seismic zoning policy.

Ground response map Shows how unconsolidated geologic material above bedrockmodifies bedrock shaking beneath a building; generallyconducted at the community level; most larger communities ofwestern Oregon are complete. Used for prioritizing efforts.

Site specific study Shows shaking potential at a site based on a site study;required for many larger and more critical structures.Used for specific engineering decisions.

FEMA 154 of buildings Sidewalk review of structures to generally suggest statisticallyhow they might behave in an earthquake. Used to prioritizebuildings for further study.

FEMA 178 of building Structural review of a building from the inside by a qualifiedprofessional to define how it probably will behave in anearthquake and to identify recommended upgrade.

FEMA 273 of building Innovative analysis of a building to show ways in which itmight be rehabilitated to meet stated standards in a statedearthquake.

LANDSLIDE Regional landslide map General map showing general landslide distribution inferredfrom general features and geology; used for general policydevelopment and to identify target areas for more detailedmapping.

Subdivision or local Local landslide map keyed to extent of local development suchlandslide map as a subdivision; needed to manage non site specific causes of

slides such as regional drainage, cumulative runoff, cumulativeerosion, and problems associated with lifelines such as roadsand buried utility lines.

Site-specific map Site-specific map used to manage or regulate hazard and riskunique to the site; site specific studies alone do not alwaysaddress cumulative problems.

COASTAL Regional coastal General map showing general distribution and rate of coastalEROSION erosion map erosion inferred from general features, historic data and

geology; used for general policy development and to identifyareas in need of more detailed study.

Littoral cell Map characterizing erosion and deposition within a littoral cellerosion map and based on understanding of the geologic processes in the

littoral cell; for bedrock reaches geologic processes andlandslides are key components; for sandy reaches and spits;storm driven events and wave models may receive emphasis.

Site-specific study Site-specific map used to manage problems unique to the site;site specific studies alone do not always address cumulativeproblems.

(Continued on next page)


Appendix 4. Specific hazard characterization (continued)

GEOLOGICHAZARD CHARACTERIZATION COMMENTS

VOLCANIC Ash zone map Specifies probable ash falls around a volcano and considersACTIVITY wind directions, eruption size, and proximity to the vent.

Debris torrent map Specifies probable extent of diverse volcanic debris that can flowdown valleys from a volcano. Based on prior volcanic behaviorand surrounding topography.

Specialized map Considered specialized features associated with the volcano suchas existing lakes or unusual prior activity such as lateral blasts.

TSUNAMI Coast-wide general General map published by DOGAMI and formally adopted bytsunami map the Governing Board to implement SB 379 (1995) (for selected

new construction under building codes regulations) based onsimple computer model and general geologic evidence; depictsgeneral distribution of the average tsunami.

Modeled bay tsunami Tsunami map for a single bay based on complex computer modelmap of water behavior combined with all available field data; can be

adopted by DOGAMI as a SB 379 map by action of theGoverning Board.

Community A version of the Modeled Bay Map, which is given moreevacuation map conservative distributions of the tsunami for increased safety

because it guides simple evacuation rather than regulates someselected buildings under the building codes regulations.

Site-specific DOGAMI can grant exceptions to the restrictions on selectedtsunami map new construction in the tsunami inundation zone defined by the

SB 379 maps. Such exceptions may rely on site-specific tsunamiinundation maps.

FLOOD National flood maps Maps issued by the Federal Emergency Management Agency toimplement the National Flood Insurance Program. Maps areprobabilistic and subdivide flood areas into zones of varyingrisk; quality of maps is under ongoing discussion. Maps do notinclude tsunami zones as such or torrential channel floods.

Other flood maps Other types of flood maps depict channels subject to torrentialor flash floods, tsunami zone of various types, lowland floodingof nonprobabilistic nature, or specific flood events.

STREAM Stream erosion maps These maps are rare and there is no standardized approach.BANK For the proper management of floodplains maps are neededEROSION which show areas of progressive stream bank erosion, areas of

deposition, areas of prior channel change, reaches of rivers withunstable channels and areas of probable future overflow infloods.


Appendix 5. Multi-hazard relationships

GROUND

FLOOD SLIDE TSUNAMI RESPONSE

SLIDE • Actions to avoidslides may poseflood problemsand vice versa.

· • Drainage controlsmay aggravateflooding, waterquality or sliding.

TSUNAMI • The two differ in • Avoidance ofterms of size, tsunami zoneflows of water, may introducehazard; cannot slide hazards treat the same. that need to be

• Regulations for addressed attsunamis are alternativebuilding specific. locations. Slide

avoidance should not drivedevelopment intotsunami zone.

GROUND • Structure • The two are • Styles ofRESPONSE strategies for compatible. construction to

floods may However, avoid tsunamiaggravate ground earthquake- developed inresponse risk. induced quake deficientStrategies for landslides are not areas may not beground response the only kinds of appropriate formay conflict with slides to address. quake threatenedflood strategies. areas.

COASTAL • No readily • The two are • Removal of logs • No apparentEROSION apparent compatible. to avoid battering conflicts at

problems. • Avoiding coastal rams conflicts this time.• Flood control erosion with with leaving of

structures locally structures can logs to forestallcan starve beaches promote erosion storm drivenin the long term. and sliding erosion.

elsewhere.


Appendix 6. Geologic hazard risk reduction by state and local agencies

AGENCY ROLE AND STRENGTHS CONDITIONS INVITING PARTNERSHIPS

OEM • Conduit for federal funding after • Emphasis is primarily on post-disasterOFFICE OF a disaster response·EMERGENCY • Close coordination with local • Little geotechnical expertiseMANAGEMENT contacts internally·

• Broad responsibilities in disaster • Focus of some federal recoveryresponse and interest and activity programs may emphasizein risk reduction restoration of public facilities and

• New focus on development of assistance to individualregional mitigation plans and homeowners at the expense ofmulti-objective initiatives proactive regional strategies

DLCD • Oversee planning on community • Focus is regional or community-wideDEPARTMENT OF or area basis and not building specificLAND • Oversee Goal 7 (natural hazards) • Little geotechnical expertise withinCONSERVATION AND and Goal 17 (beaches and shore the agencyDEVELOPMENt lands) • Goal 7 efforts for many

• Oversight of federally funded communities in the state areCoastal Zone Management weak on adequate hazardProgram characterization

DOF • Extensive field-based knowledge of • Small size of staff dedicated toDEPARTMENT debris torrent risk in mountainous geologic hazardsOF areas and forest lands • Incomplete linkages to manyFORESTRY • Agency lead on debris-flow agencies and communities

warning system needing expertise

LOCAL • Central role regarding local • Insufficient technical backgroundCITIES AND concerns • Lack of proper hazardCOUNTIES • Must live with the solutions at characterization·

local level • Possible pressure of local politics• Unique access to some federal

funding programs

BCD • Building specific approach suited • Treatment of variable nonstatic orBUILDING to hazards offsite ground conditions is weakCODES • Site-specific reports required for • Major focus is building specificDIVISION seismic hazard and not regional or

• Restrictions on use of earthquake- community-wide·damaged buildings • No specific authorities for

• Exemptions to building seismic rehabilitation ofclassifications relative to preexisting structurestsunami zone restrictions

DOGAMI • Centralized source of information • Small size of staffDEPARTMENT on geologic hazards for the state • Incomplete linkages to manyOF of Oregon agencies and communitiesGEOLOGY • Partnership style and community needing expertiseAND approach • Specific lead roles for someMINERAL • Strong public education aspects of risk reduction assignedINDUSTRIES commitment and program to other agencies


Appendix 7. Range of strategies to reduce risk

This section provides a generic summary of vari-ous techniques of risk reduction that have beentried for various hazards from place to place inOregon. Depending on the nature of the hazard,level of risk, financial considerations, and stan-dards any one of these techniques has beenfound to be the best approach at one time oranother at a given location or another.

A particular strategy that works in one placemay not work in another. This is particularlytrue in Oregon, where conditions of geology, cli-mate, culture, and cost vary from place to place.Accordingly, flexibility in approaches is one ofthe core messages of this reference manual.

Here we encounter a key point in the reductionof risk from threats as complex as geologic haz-ards. An understanding of the range of optionsand their respective proper applications is arequirement for proper strategy development.Effective risk reduction requires an understand-ing of the choices.

There are tradeoffs involved for all mitigationoptions. The less rigorous strategies bring withthem the possible risks of not properly address-ing issues of public safety, health, or welfare. Yetin situations involving little risk and less inten-sive development, implementation of less rigor-ous strategies may be appropriate.

The more restrictive strategies may bring withthem the risks of higher costs, and possibly unac-ceptable limits on personal property freedoms.Yet choices of this type sometimes are judged asbest for the community.

For any selected strategy, ongoing communica-tion within the team and with the scientistsshould assure that the action reasonably reducesreal risk while it balances considerations of cost,economics, safety, resource protection, personalrights, and liability issues.

Choices should also work in terms of naturalprocesses. The challenge is to select options thatbalance losses against gains in a manner accept-able to the community.

The format of the following table is designed toassist the reader.

• The various options for risk reduction are list-ed in general order of increasing regulation oreffort. Risks of high hazard and frequentoccurrence generally are more properlyaddressed with options near the end of the list-ing. Hazards of low frequency or impact aremore appropriately addressed with options atthe front of the listing.

• The first column breaks the larger listing intomajor categories.


Appendix 7. Range of strategies to reduce risk — Table

GENERAL SPECIFIC LIKELYACTION STRATEGY LEAD AGENCY EXAMPLES AND COMMENTS

DO NOTHING Actively or Any It is possible to administratively overlook hazards orABOUT passively ignore ignore their presence leaving their treatment to routineGEOLOGIC the possibility operations. If risk is low doing nothing formal at theHAZARDS of the presence governmental level may result in no adverse

of hazards consequences. Proper characterization of the hazardsassists in judging the adequacy of this option.

Misplace Any Good hazard information sometimes does not find itshazards reports way to the user owing to other priorities. This is notor fail to acceptable practice, but has been allowed to happen indistribute them several jurisdictions. Sometimes hazard reports areeffectively presented in such a technical manner or are so poorly

presented that they are misplaced or overlooked simplybecause their content is not fully appreciated.

Assign low Any Various hazards can be regarded as too low in prioritypriority to to warrant consideration. Hazards of vague impact orhazards actions; long time frames may be treated in this fashion. Riskgo on to other based decisions are acceptable; if defined risk is low,problems the need to mitigate is also low. If low priority is assigned

it should be done based on objective analysis and notsimply on a lack of appreciation of the issues that mightbe present.

DEVELOP Develop vague Any General discussion of hazards can appear in reportsONLY reports for without leading to any particular insights or actions.GENERAL policy offices Awareness is served, but risk reduction is notIDEAS ABOUT with no specific accomplished. Generalized discussions of hazards areGEOLOGIC action track common in any of a variety of planning documents.HAZARDS Often the information does not appear to lead to any

decisions one way or the other. Regardless of the degreeof generality, it is important that the information bechanneled to a discrete decision, even if the decision forthe time being is to do nothing more. Where no decisionis linked to the information, progress towards riskreduction has not occurred.

Provide vague Any Planning documents can state a concern for hazards,language in but can fall short of actual action plans to do anythingplanning about them. Planning documents can recommenddocuments or action by others, but follow-through may not beother policy provided. An example is a general treatment of adocuments that hazard in a comprehensive planning document thatmight lead to does not lead to a discrete action to reduce risk.action eventually General policy language in a planning document

represents work undone, but does provide the benefit ofdefining a start point for further policy discussions.


Appendix 7. Range of strategies to reduce risk — Table (continued)


DEVELOP Adopt small-scale Planning This approach serves to flag areas of concern in terms ofGENERAL MAPS maps with general office future development. By itself it does not accomplishTHAT MENTION information to focus risk reduction, but coupled with the focusing of furtherTHE RISK OF attention into some work in hazardous areas, it sets into play a process thatGEOLOGIC areas can accomplish risk reduction. Such general portrayalsHAZARDS may prompt individual actions later for risk reduction in

target areas or may eventually serve as the basis for policyaction by the community. For areas of only long-termfuture concerns such maps may be valid ways to flagareas of need of greater attention in the future whendemographics are more demanding. Maps of this sort maybe of greater value to counties than to communities withgreater developmental pressures. They can be appropriatefor depicting large scale hazards of low frequency, such assome volcanic hazards.

Develop narratives in Planning It is common to find general hazard discussions inplanning documents office planning documents that describe hazards and lay outwith nonspecific future options for treatment. Depending on the use ofobservations and place the document, this approach may be an appropriate stepinto policy documents toward increasing governmental awareness orto keep the issue alive formulating action at a later time. Areas not under

development pressure may be properly served for a whilewith this kind of flagging, for example.

Adopt or distribute Planning In an attempt to fix the problem this approach is some-borrowed regulatory office times pursued. It includes the notion that ordinances cantext from other areas. be imported verbatim from other areas. In areas of diverseFor example, geologic conditions such as Oregon, this approach isordinances from one usually unwise and is not as effective as ordinancecity are sometimes development based on characterization of the hazardadopted by another area in question. In general it is necessary to characterize

the hazard at the location in question before effectivemitigation can be implemented. However, generallanguage in ordinances from analogous areas often canprovide a useful starting point for developing anordinance somewhere else.




DEVELOP Develop Planning Larger scale maps that properly depict the hazard, itsGOOD GEOLOGIC large-scale maps office variations, and its causes can be useful tools inHAZARD MAPS of hazard areas formulating mitigation strategies appropriate for theTHAT FOCUS and adopt specific area in question. The key is in finding the properON THE requirements balance of effort, expense, and rigor among involvedSPECIFIC HAZARD aimed at tying parties. In much of the northwest we have learned, forFOR THE SPECIFIC information to example, that hazard depictions at a 1:24,000 scale inAREA property documents. communities are not adequate to properly characterize

Included are the hazard and to prescribe effective strategies for riskrecordation on reduction. As larger and larger scales are pursued it isdeeds and waiver important that the distinction between a policy map at onerequirements scale not be blurred with site-specific maps intended for

individual parcels. It is also important to appreciate thatsite-specific maps alone generally do not solve hazards ofa regional nature.

Develop or Planning Site-specific studies address factors and impacts at the siterequire specific office and are appropriate for hazards that are limited incharacterization distribution to specific sites. However such studies mayand remediation overlook regional factors and causes that may also be atfor the site in play. This approach works for small hazards, but isquestion inadequate for regionally driven hazards (which are

handled below). Site specific studies and risk reductionoften must be integrated with more regional strategies toeffectively mitigate hazard risk in areas of regionalhazards like large landslides. This also is particularly truewith coastal erosion issues, where the behavior of littoralcells must be appreciated to solve local coastal erosionissues.




PROVIDE PUBLIC Require disclosure Local or The idea is to not allow owners to pass EDUCATION TO statements state properties of risk on unsuspecting buyers. FOREARM THOSE in specified government Requirements to disclose information should focus MAKING situations. This at policy on information of a site-specific nature since the DECISIONS IN approach level overall context is site specific. This particular THE HAZARD appears to serve approach may be reasonable in its administration, if AREA the buyer, but it is focused on areas for which reasonable chances (continued may be difficult of risk have been predetermined. Otherwise it can on next page) to formulate and be burdensome on areas with no risk.

may overlookother aspects ofthe hazard

Require recordation Local or This is a specialized category of disclosure in whichof eminent hazard state key areas are properly recorded so that they surfaceareas for discovery government in title searches prior to closing of sales. Regionalin title search at policy hazards of proper characterization can be handledactivities level in this way provided the payoff justifies the

administrative investment. A disadvantage is thatrecord keeping may be sufficiently inefficient thatproperties that are properly mitigated eventuallywill still show up as hazard threatened in a titlesearch.

Prepare and Any Public education is a viable strategy wheredistribute numerous members of the public may be involvedpublications or and other options are not effective. For example,other releases warning signs are a proper choice along cliffs, inof the hazard tsunami danger zones, in areas of dangerous surf, orinformation in some landslide areas. This approach relies on the

“buyer beware” or “visitor beware” principle andprovides reasonable prospects of the buyer or visitorbeing informed. It also provides information toofficials needing to know about hazards beforemaking decisions. Proper information can guide avariety of proactive policy discussions.




PROVIDE PUBLIC Provide for Emergency For specific areas of fairly frequent high impact hazardsEDUCATION TO realistic and management this mechanism provides mainly for public safety. ItFOREARM THOSE reliable or addresses lives rather than property. Owing to highMAKING warning Any investment and maintenance factors this strategy generallyDECISIONS IN systems is limited in application to areas of very high risk.THE HAZARD Tsunami hazards threaten transient populations and lendAREA themselves to signing along beaches for general public(continued warning and for warning sirens in at-risk communities forfrom previous evacuation. On a broader scale Oregon has implemented apage) statewide warning system based on existing communication

systems and identification of threshold rainfall events. Insome areas of the world mechanical warning systems aredesigned to function near the bottom of extremelyhazardous debris avalanche channels.

Public Any An agency with knowledge of the hazard can developeducation strategies of focused outreach to assure that major players

and the public know what the problem is and are assistedin finding ways to address it. The effort can focus thegeneral public in an area of hazard or can rely on focusedcommunications with particular interest groups orstakeholders. Clear decisions regarding whether to pursuegeneral or focused efforts should be made to better assureeffectiveness. Techniques for outreach should strategicallyaddress the characteristics of the target audience. Forexample, the use of signs along beaches for tsunamisrecognized that the use of signs at the location of thehazard is clearly an effective way to meet a transient andchanging population (beach users and tourists). Teamefforts can be effective, such as the landslide brochuredevelopment, which was part of the Governor's debrisavalanche strategy. For tsunamis, a wide array of outreachproducts are available including bookmarks, brochures,informative mugs, and videos.




FACILITATE Provide for land Local or state Communities such as Astoria have engaged in landVOLUNTARY trades or land government trades in which hazardous ground traded from theMITIGATION purchases to at policy level private sector to minimize their losses in exchangeWITH SPECIFIC remove those at for other land. The community then uses the landOPPORTUNITIES risk for preferred community uses such as parks. Key(continued ingredients are an extreme desire for the public toon next page) have access to a solution plus the availability for

land to trade by the community. This technique hasbeen used to solve other land use problems.

Provide for Local or state As with the flood insurance program these programsinsurance, either government spread the risk, but also are keyed to efforts tothrough at policy level reduce the risk, by requiring reasonable mitigationgovernment by participants. This technique requires a intensiveor through administration and is most appropriate where riskprivate sector is complex, widespread and of large size, and where

occupation of the hazard area seems necessary (i.e.,earthquakes). For complex hazards of difficultcharacterization and many causes (some of whichcan be self-induced), such as landslides, insurancemakes less sense. As people learn of the hazardthose not at risk choose not to participate, thusrendering shared risk not viable.

Develop incentive Local or state To reduce some risks, tax credits may be appropriate.programs leading government Generally this is true if the induced mitigationto self-initiated at policy level through private action adds up to a major publicmitigation of the benefit in the long run. Seismic rehabilitation ofspecified risk selected buildings is a candidate for this kind of

strategy.

Remove Local or state Various governmental programs involve generaldevelopment government incentives such as cost breaks for infrastructure andincentives in at policy level tax incentives. These can be structured with appropriateareas of limitations so that they do not apply in areas ofgeologic risk known unacceptable geologic hazards. For example,

tax breaks for new industrial development can bestructured to not apply in flood plains.




FACILITATE Provide for Emergency After losses have occurred at a site reconstructionVOLUNTARY engineered solutions management using engineered solutions to the problem mightMITIGATION through disaster- or be appropriate where relocation is not possibleWITH SPECIFIC based reconstruction Any and where expense is justified by the results;OPPORTUNITIES such things as rehabilitation of bridges damaged(continued in a flood or an earthquake fall into this category.from previous For a large slide in The Dalles in the middlepage) 1980s, slide drainage of groundwater was

implemented because the city was already inplace and it provided a much more acceptablesolution than moving the threatened buildings.The geology was permissive of a dewateringsolution. In other communities such as Kelso,Washington, the geology renders dewatering tobe not feasible.

Develop Local or state For some regional hazards the most effectivepartnerships of government solution is to promote private sector effortsimpacted audiences at policy level toward team problem solving. Such an effort mayincluding self-funded or be characterized by recognition of a commonimprovement districts Neighborhood specific goal, proper information in advance, andto provide creative group creative thinking. Tactics may include taxingmitigation districts with funding aimed at effective

solutions. This approach may be needed inhazard areas where existing developmentprecludes many of the other options. Littoralcells, regional landslides, and large streamerosion areas lend themselves to this kind ofstrategy. Some communities in other states haveformed Geologic Hazard Abatement Districtsunder the general guidance of state law.




REQUIRE Develop restrictions Planning Where land use zones can effectively address theMANDATORY through zoning office causes of the risk in a manner acceptable to theMITIGATION users, this approach may provide much of theOF GEOLOGIC risk reduction. Approaches such as this lendHAZARDS themselves to regionally driven geologic hazards(continued such as large, relatively active landslides.on next page) Alternatively, in Oregon earthquake ground

response for technical reasons does not lend itselfto risk reduction through direct zoning action,because within zones of given hazard it is thebuilding type that most determines the risk, andnot the zone itself.

Develop building Building Some hazards do not lend themselves to the toolscode controls that codes of land use zone regulation, but can be addressedspecifically address in the manner of construction of buildings.the hazard Seismic codes for buildings are an example.

Ground response data can guide or influencerequirements for specific buildings. Also,prevention of slides that might be caused by sitepreparation can be avoided through implementationof grading codes. General grading codes do not,however, directly address hazards posed bylarger preexisting slides or geologic materials ofuniquely unstable slope characteristics.

Adopt grading Planning Specialized regulations focused on the risk areasordinances, hillside office and the causes of the risk can provide the basisdevelopment for ongoing management strategies to mitigateregulations, the risk long-term, as land use evolves in the areasubdivision ordinances, of concern. Examples include: limits to grading,etc., which are keyed to conformance to topography, setbacks, openthe characterization of space, clustering, lot size and shape, vegetation,the hazard. Also included road layout, and road engineering. In general,here might be some one factor that simply must be addressed in thesegeologic hazard strategies is proper management of storm runoff.abatement districts. In slide-prone terrain, piecemeal approaches to

the runoff problem inevitably lead to slideproblems at least on a local basis. Many suchslides can be avoided with proper runoffmanagement.




REQUIRE Construct protective Local or state Where cost of the hazard greatly exceeds cost ofMANDATORY structures in areas government the structures engineered solutions may beMITIGATION of particularly high at policy level justified. A full range of possible solutions forOF GEOLOGIC risk each hazard is available; considerations of costHAZARDS generally limit the number of realistic choices, if(continued any, for a specific problem. Examples includefrom previous walls to divert debris avalanches, for example.page) On a larger scale flood protection dams and

levees are other examples. Increasingly the sideeffects of hard solutions are being evaluated interms of impacts on watershed values. Yetanother example is rip rap along coastlines. Herevarious policies may prohibit use of rip rap ingiven situations. Also, technically soundevaluations of the long- term effect of rip rap onthe property in question and the rest of thelittoral cell must support the decision to riprap, or the solution will only be temporary.

Require engineered Building Involves requiring the private sector to spend thesolutions in the codes money for risk reduction as part of the constructionactual construction or improvement of the structure. On a building-of the building specific basis, seismic zones currently define a

wide range of required engineering solutions. Infuture years, requirements may be more directlylinked to modeled probabilistic earthquake activityrather than formally defined zones. Specialtyrequirements can be developed for constructionin tsunami zones. For non-inhabited structures avariety of regulations or handbooks provideengineering requirements for power plants,dams, substations and other structures. Properdesign presumes proper understanding of therisk. In Oregon the State Geology Department(DOGAMI) peer reviews the field based geologichazard findings upon which engineering designsare based.




IMPLEMENT Prohibit some new Building For some really hazardous areas prohibitions ofPROHIBITIONS construction with codes some types of construction are viewed as necessary.AGAINST specified exemptions Exemptions are designed to balance otherCONSTRUCTION for certain situations considerations or circumstances. The tsunamiIN AREAS OF that simply are not restrictions for certain kinds of critical and specialGEOLOGIC workable occupancy structures along the coast are a goodHAZARD example. To the extent the requirements focus on

certain kinds of buildings only, and do nototherwise control activities in the hazard zone,the regulatory arm that is most appropriate isBuilding Codes, according to wording of thestatute.

Prohibit new Building For some really hazardous areas prohibitions ofconstruction with codes some types of construction are viewed as necessary.exceptions for or Exceptions can be provided where risk isfacilities that can Planning addressed in other ways or where further analysisdemonstrate lower office shows that an exception is justified through betterthan anticipated understanding of the hazard. The tsunamihazard or risk restrictions along the Oregon coast are a good

example. Where most kinds of buildings arerestricted, the planning office probably is mostsuited to the task. Where only a few kinds ofvery specific buildings are involved a BuildingCodes approach may make more sense.

Prohibition Planning Simple prohibition of construction is an optionwithout office for really serious situations. Examples are rare.exemptions or Here the focus is on the region rather than selectedexceptions buildings; regulation by the planning office

makes the most sense. In Crescent City, California,much of the area destroyed by the 1964 tsunamiis now dedicated to parks and greenway ratherthan construction. Some landslide areas andcoastal erosion areas in Oregon probably shouldeither be set off limits for construction or shouldrequire very intensive mediation. Some properlydelineated debris torrent channels should be offlimits to construction.




PROVIDE FOR Provide for Local or state This strategy addresses risk in structures that areRETROACTIVE rehabilitation of government in place when the hazard is recognized.ACTIONS FOR selected structures at policy level Prioritized seismic rehabilitation can be an example.PREEXISTING or classes of Cost benefit is a primary consideration.STRUCTURES IN structures, using Rehabilitation can be keyed to passive triggers orAREAS OF passive triggers otherwise prompted. Good information on groundGEOLOGIC response, building-type inventory (using FEMAHAZARDS 154, 178, or 273 for example), and probabilistic

risk can assist the community in making decisionsregarding the value of rehabilitation programs.Portland has codified such a program.Remediation of buildings in flood plains or slideareas might also be required as a conditionof financial assistance after a disaster.

Provide for Local or state This strategy addresses risk in structures that arerehabilitation of government in place when the hazard is recognized.structures or at policy level Prioritized seismic rehabilitation can be an example.classes of Cost benefit is a primary consideration. Activestructures with triggers apply to more serious situations. Goodmandated active information on the hazard, building inventory,triggers and probabilistic risk can assist the community in

making decision regarding the value ofrehabilitation programs. Mandated triggersshould be reserved for the more serious threatsto human safety.

Require removal Local or state This approach is used where imminent destructionof structures from government is anticipated; homes have been removed fromhigh risk areas at policy level landslide areas, for example, as noted above. In

the option described here the emphasis is onmandatory action as opposed to voluntary orincentive driven removal. Good information onthe hazard, building inventory, and probabilisticrisk can assist the community in making decisionregarding the value of removal programs. Thisparticular course of action is pursued only veryrarely. Structures that have received repeateddisaster assistance from public funds are some-times discussed in connection with this concept.


Appendix 8: QuestionsThe following questions can help to identifyinstitutional impediments:

1. Is the jurisdiction that is characterizing thehazard satisfied with only characterization, oris it reaching out to policy persons to helppromote the understanding that is also need-ed for effective risk reduction?

2. Since Mother Nature speaks indirectlythrough scientific principles and naturalevents, it is important that the policy personbe listening to the interpreters (geologists,engineers, etc.) to better understand the haz-ard before deciding how to deal with it. Areexperts being consulted to determine theprobable effectiveness of proposed strategies?

3. Since Mother Nature does not go to meetings,have policy makers solicited timely advicefrom the interpreters during policy develop-ment? Or have they structured policy meet-ings to focus solelyon the positions of“stakeholders”and forgotten thatMother Naturecontrols the ulti-mate outcome?

4. Because MotherNature may com-plicate the situa-tion with the pres-ence of multiplehazards, has con-sideration been made of how a solution forone hazard may aggravate another hazard?Often the solution proposed for one hazardmay aggravate another hazard. Have policymakers tapped ongoing input from experts toassure that corrective actions do not actuallyadd to overall risk?

5. In efforts to follow clear procedures, havepolicy makers successfully linked characteri-zation, conversation, and risk reduction indecision-making or have they built procedur-al walls between them? For example, in fund-ing opportunities, are communities expectedto adopt policy in the absence of requisitehazard characterization?

6. Is the jurisdiction that is characterizing thehazard providing opportunities to communi-

cate with the community and the risk reduc-tion team? Or are schedule and budget morerestrictive and dictate termination of involve-ment by scientists once the map is made, butbefore policy decisions begin to be made?

7. Do the funding sources for risk reductionprescribe funding criteria that connect thefour components of success (characterization,team effort, strategy selection, and institu-tionalization) or do their criteria unnecessari-ly eliminate one or more of these while pro-moting the others?

8. Does the community that is attempting toreduce risk develop strategies keyed to localconditions or does it merely import regula-tions developed elsewhere under a differentset of circumstances?

9. In pursuit of the goal to reduce risk for acommunity, are those involved systematicallyidentifying all significant hazards or are theycontent to pursue just those hazards that are

readily apparent tothe public?

10. Have communi-ties dealing withhazards fallen in thetrap of simply“delineating haz-ards” and asking for“site-specific stud-ies” later? Or arethey attempting tocharacterize the haz-ard (where it is, how

bad it is, how often it occurs, and how humanactivities change these answers), then askingfor more of the right kind of information sothat more effective policies and strategies canbe formulated?

11. Does each jurisdiction, according to its ownspecialized interests, consider itself theleader? Or does it recognize and proceedwith the conviction that science, buildingcodes, response planning, technical informa-tion, and local values are all parts of a broad-er team effort involving unique contributions,ongoing communication and teamwork?

A case study using the principles inthis manual can be found in A sum-mary of risk reduction of geologichazards: A technical reference man-ual for Oregon (Special Paper 30).The City of Salem, Marion Countyand Polk County worked together tomitigate landslide hazards in theSalem Hills.

geologic hazards: reducing oregon’s lossesbrownk/es105/reducingoregons... · special paper...

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