paul whitmore, noaa/nws west coast/alaska twc, july 28, 2007 uw educational outreach – tsunami...

Sponsored by NOAA and USAID under the U.S. Indian Ocean Tsunami Warning System Program

Paul Whitmore, NOAA/NWS West Coast/Alaska TWC, July 28, 2007UW Educational Outreach – Tsunami Science & Preparedness Program (Su 07)

U. Washington Tsunami Certificate ProgramCourse 2:

Tsunami Warning Systems

Session 7Tsunami Warning Data Processing

July 28, 2007 1:15-2:45pm



Outline

• Seismic Data Processing– Seismic Basics

– Seismic Processing Architecture

• Sea Level Processing

• GIS

• Data bases

• Forecasting– Techniques

– Exercise


Paul Whitmore, NOAA/NWS West Coast/Alaska TWC, July 28, 2007UW Educational Outreach – Tsunami Science & Preparedness Program (Su 07)Earth Cross-section



Seismic Basics – Earthquake Rupture

Earthquake Strain Build-up and Rupture similar to bending a plastic ruler

• Build-up of Stress (strain energy)

• Can’t predict where or when ruler will break

• Breaks at weakest point

• May hear precursors

• Sound of breaking same as seismic waves




Elastic Rebound Theory

• Henry Reid – 1910

• Based on studies of 1906 San Francisco earthquake– Strain Builds up

– When strain exceeds fault strength, fault slips

– Elastic energy released at time of slippage




• Body Waves – travel through the earth– P Waves

• Sound Waves

• Particle motion in the direction of propagation

– S Waves

• Particle motion perpendicular to the direction of propagation

• Generally caries more energy than the P wave

• Surface Waves – travel around earth’s surface– Rayleigh Waves

• Elliptical motion in direction of propagation

• Size of ellipse related to wave period

• Dispersive – peak velocity at about 50s period

– Love Waves



Seismic Basics – Earthquake Rupture• Three basic types of earthquake

rupture– Reverse Fault

• Hanging wall moves up relative to footwall

• Common in compressive environments like subduction zones

• Thrust faulting is a special type of reverse fault

– Shallow dip angle

• Most major earthquake-generated tsunamis are triggered by this type of faulting




• Three basic types of earthquake rupture– Normal Fault

• Hanging wall moves down relative to footwall

• Common in extensional environments like basin and range provinces (and within subducting plates)

• Many earthquake-generated tsunamis are triggered by this type of faulting




• Three basic types of earthquake rupture– Strike-slip Fault

• Fault motion is horizontal

• Faults are normally high angle to surface

• Common in mid-ocean ridges and transform plate boundaries

• Not as likely to trigger tsunamis as dip slip quakes, but many large local tsunamis have been triggered by this type of quake

• Right lateral v. left lateral




• Parameters which define earthquake rupture– Strike

– Dip

– Slip

– Length

– Width

– Depth

– Moment

– Rupture Velocity

– Slip Velocity

– Rock Properties



Seismic Basics – Earthquake Location

• Four unknowns– Origin Time

– X/Y/Z

• Solve using phase arrival times– Needs good velocity model of earth

• S Minus P time approach– S-P time increases with epicentral distance

– Each station which records S and P waves provides a distance from station to epicenter

– Three stations with S-P needed for location




P-wave only method

The location has 4 unknowns (t,x,y,z) so with 4+ P arrivals this can be solved.

The P arrival time has a non-linear relationship to the location, even in the simplest case when we assume constant velocity – therefore can only be solved numerically

Use a Least squares method – minimize residuals between observed and calculated travel times




• Automatic Locations– Seismic data analyzed by routine which determines onset of P wave

– P-time sent to associating/locating algorithm

– Associator attempts to split P-times into buffers which contain P-picks from same earthquake

– When 5 picks accumulate in a buffer, quake will automatically locate.



Seismic Basics – Earthquake Magnitude

• Magnitude– 1935 Charles Richter related amplitude on a seismometer to energy

release and created a “magnitude” scale

– Many scales used, though most use the same energy/magnitude relationships as devised by Richter

– Each magnitude scale is appropriate for a certain type or size event.

– All magnitude scales are logarithmic

• 1 unit on scale equates to 10x the ground motion

• 1 unit equates to approximately 32x energy release

– Tsunami Warning Systems are concerned mainly with fast evaluation of large earthquakes

– Four different types of magnitudes computed at WCATWC




• Body wave and Local Magnitude (mb and Ml)– Evaluated after automatic or interactive P-pick

– Determined very quickly after event

– Determined on short period filtered data (0.3 – 3s period)

• Max amplitude (and corresponding frequency) in first 15 cycles of waveform is used to determine mb once location is known

• Max amplitude (and corresponding frequency) beyond 15 cycles and less than 2.5 minutes is used to determine Ml once location is known

• Based on epicentral distance, mb or Ml is computed– mb > 15 degrees

– Ml < 9 degrees

• Ml generally accurate in the range 0-6.75 for shallow quakes

• Mb generally accurate in the range 4.5-6.5 for any depth quakes




• Surface Wave Magnitude (Ms)– Evaluated cycle by cycle on surface waves after location determined

– Takes longer to compute than mb/Ml

– Determined on long period filtered data

• Automatically computed for all quakes over magnitude 5

• Based on location, Rayleigh wave start time determined

• Signal evaluated for one minute before R-wave to 30 minutes after– Period range 18-22 seconds used

– Epicentral distance must be at least 5 degrees

• Accurate for shallow quakes in the general range 5.5 – 7.75

• Ms/mb good discriminator for deep quakes




• Moment Magnitude based on integrated P waveform (Mwp)– Evaluated 50s, 100s, 150s, and 200s after P-pick

– Developed in 1990s by Tsuboi - ERI

– Determined on broadband data

• Signal-to-noise ration checked, must exceed threshold value

• The longer the frequency response of instrument, the better the result

• Velocity signal integrated twice– Time of integration dependent on corner frequency of signal

– Mwp based on integrated displacement signal amplitude

• Accurate for quakes in the general range 5.5 – 8.0

• Fastest way to determine moment magnitude




• Moment Magnitude based on mantle waves (Mm)– Evaluated after 11 minutes of Rayleigh wave signal is recorded

• Epicentral distance must be greater than 16 degrees

– Developed in 1990s by French Polynesia TWS group

– Determined on response-corrected, broadband data

• Spectra computed for 11 minutes of Rayleigh wave data

• Maximum spectral amplitude chosen

• Magnitude computed based on amplitude and rock properties over source/receiver path

• Accurate for quakes in the general range 6.25 – 8.75

• Most accurate TWS method to determine moment magnitude for really big quakes



Seismic Basics – Earthquake Magnitude• Inversion techniques

– USGS techniques

• Compare observed seismogram to a synthetic signal

• Produces – Moment magnitude

– Depth

– Strike

– Dip

– Slip

– Moment Tensor

• 12-20 after O-time to compute



Seismic Processing Architecture

• USGS Earthworm Architecture– Developed as tool for regional

networks

– Used as basis for U.S. Tsunami Warning System to exchange seismic data

– Earthworm Philosophy

• Modular Approach

• Each module performs one function

• Modules attach to rings (shared memory)

• Modules communicate by sending messages via the rings



Seismic Data Acquisition at the WC/ATWC



Seismic Data Processing

• WCATWC Earlybird System– Developed for fast processing of Big

earthquakes

– GUIs to refine automatic results

– Redundant backup operates concurrently



Seismic Data Processing (1)

• Real-time processing– Seismic alarms are triggered based

on strong signal at one or more stations

– All data processed at 20-25 sps to determine onset of P wave

– Automatic locator sorts P-arrivals into buffers for different events

– Locations computed when buffers fill up with 5 P-picks

– Time to first auto-location depends on station density

• High density -> < 1 minute

• Low density -> 5-10 minutes




• Geophysicist refines automatic location

• Earthquake depth estimations made both automatically and interactively

• Initial locations accompanied by Ml/mb magnitudes

• Mwp compute approximately 60s later

• Initial analysis complete




• After initial message disseminated, processing continues:– Refine Mwp (5-15 minutes)

– Compute moment tensor (12-20 minutes)

– Compute Mm (20-60 minutes)



Sea Level Processing

• Geophysicist refines automatic location

• Earthquake depth estimations made both automatically and interactively

• Initial locations accompanied by Ml/mb magnitudes

• Mwp compute approximately 60s later

• Initial analysis complete



Sea Level Processing

• Data written to disk in common format

• Display programs retrieve disk data

• Display in detailed or strip chart view– Data de-tided

– Low pass filtered

– Interactively measure amplitude/period

• PTWC Tide Tool– Contact Stu Weinstein at PTWC



Sea Level Data Format

Adak,_AK 9461380 NOS Continuous 51.863 -176.632 20070514

NGWLMS m UTC 1 min MLLW WCATWC Unfiltered

1_minute_NOS_data_via_GOES

Data Format: SampleTime(epochal 1/1/1970) WaterLevel SampleTime(yyymmddhhmmss)

1179100800 1.288000 20070514000000

1179100859 1.288000 20070514000059

1179100919 1.290000 20070514000159

1179100979 1.291000 20070514000259

1179101039 1.294000 20070514000359



Geographical Information Systems

• GIS uses in a TWC– Provides the analyst good situational awareness

• Relates source zone to tectonic environment

• Relates source zone to cultural and population centers

– Interactive access to historical tsunami and earthquake data bases

– Compute and display tsunami travel time maps

– Interface with forecast models

– Many types of cultural and geophysical overlays

– Produce graphics for distribution to web sites.



Geographical Information Systems

• EarthVu GIS developed at WCATWC– Uses the Geodessey Ltd Hipparchus

software as a base

– Written in C for Windows environments

– Can be re-programmed to provide outputs desired by analysts



Historical Data Bases

• Access to accurate historical tsunami and earthquake data bases is critical for TWCs– Tsunami data bases provide a method to determine what size events can

produce damage

– Provide data which can be used during an event to estimate effects elsewhere

– Prior to events, historic tsunami information can be used to help set response procedures

– Used to determine an area’s overall hazard

– Detailed historic information can be used to estimate inundation limits in some cases




• Data Sources (for example)– NOAA/National Geophysical Data Center

• http://www.ngdc.noaa.gov/seg/hazard/tsu.shtml

– Russian Academy of Sciences

• http://tsun.sscc.ru/tsun_hp.htm

– Tsunami Bulletin Board

– International Tsunami Information Center Reports

– National historic tsunami studies




• Example of WCATWC data base retrieval and GIS



Historical Data BasesAmplitude (m) Location/Damage Year

0.35 Shemya; no damage 1996

0.4 Yakutat; no damage 1987

0.5 San Francisco, CA; strong current stops ferry 1960

0.5 Port Hueneme, CA; no damage 1957

0.5 Crescent City, no damage 1994

0.5 Crescent City, CA; 1 mooring broke loose 1963

0.5+ San Diego, CA; boat/dock damage 1957

0.51 Adak; no damage 1996

0.6 Ketchikan; no damage 1964

0.6 Los Angeles, CA; $200K damage to boats 1964

0.6 Monterrey, CA; 2 almost drowned 1957


0.6 San Diego, CA; strong current, boat damage 1964

0.7 Crescent City, CA; no damage 1957

0.7 San Diego, CA; boat/pier damage (20 knot current) 1960

0.8 Unga; dock washed away 1946




0.8 Port Hueneme, CA; railroad tracks flooded 1946

0.8 San Pedro, CA; wharf flooded 1868

0.8 Avila, CA; no damage 1927

0.8 Santa Barbara, CA; no damage 1946

0.8 Santa Barbara, CA; boat damage 1964

0.8+ Los Angeles, CA; $1 million damage, 1 drowning 1960

0.9 Yakutat; Mooring torn loose 1958

0.9 Adak; no damage 1986

0.9 Shemya; no damage 1969

0.9 Anaheim, CA; boats loose, no damage 1877

0.9 Santa Cruz, CA; boats loose, no damage 1960


0.9 Trinidad, CA; cars stuck on beach 1992

1.0 San Pedro, CA; flooding, no damage 1877

1.0 Crescent City, CA; 4 boats sunk 1952

1.0 Cape Pole; log boom broke 1960



Tsunami Forecasting• Purpose

– To predict amplitudes at coast and drive proper emergency response

• Basics– Assimilate observations into numeric models

• Some techniques just use pre-computed models based on earthquake parameters without adjustment with sea level observations

– Full-ocean tsunami models compute slower than waves propagate when detailed resolution is used

• At least some part of the models must be pre-computed

– Techniques used at U.S. TWCs

• SIFT – Session 6

• TWC technique – More here

– JMA approach

• All pre-computed

• No adjustment based on observations



Tsunami Forecasting

• TWC method– Based on Zygmunt Kowalik (U Alaska) technique

• Long wave equations– Coriolis

– Bottom Friction

– Non=linear terms

• Finite Difference Approach– Space staggered grid

– No inundation

– Dynamic grid interactions

» 5’ increment in deep water

» 1’ increment on shelf

» 12” increment near shore

• Source – static vertical motion based on earthquake parameters



Tsunami Forecasting

• TWC application– Determine likely fault parameters for Pacific subduction zone quakes

– Model quakes of different magnitude in each zone (several hundred)

– Save maximum amplitudes throughout model

• During Event:– Based on quake’s location and Mw, choose most appropriate model

– Scale previously computed amplitudes based on recorded amplitudes outside source zone

– Scaling averaged as more amplitudes recorded

– Make decision on warning expansion or restriction based on predicted amplitudes

• Test on all large Previous events



Tsunami Forecasting



Tsunami Forecasting

• Pitfalls– Source region difficult to forecast

• Time constraint

• Secondary sources

– Later waves hard to forecast

– Model assumptions

• 2d

• Resolution

• Source uplift



Tsunami Warning Data Processing - Summary

1. The most important aspects of seismology to the tsunami warning system are how earthquakes trigger tsunamis and how earthquakes are rapidly characterized after an event.

2. Earthquake magnitude determination sometimes seems more like an art than science.

3. TWCs must be able to quickly process and review events. The processing software must be optimized for large events.

4. A GIS which interacts with the rest of the processes is critical at a TWC.

5. Tsunami data bases provide important information for use both before and during an event.

6. Tsunami forecasts are used to guide supplemental decisions during events.



Tsunami Warning Data Processing: References

USGS Seismology and Tsunami Warnings Training Course – CD - 2006

paul whitmore, noaa/nws west coast/alaska twc, july 28, 2007 uw educational outreach – tsunami...

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