Geologic & Natural Hazards

• Earthquakes• Tsunamis• Floods• Monsoons• Volcanoes• Asteroids

Natural Hazards

Earthquakes : Seismic waves Video of waves

The epicenter, not the “earthquake” is directly above the focal mechanism (release of energy)

Waves move in specific directionsBody WavesP : Primary waves

S : Secondary waves

Surface WavesLoveRayleigh

Earthquakes :Fault motion • Fault motion describes type of earthquake • Dip – Slip faults

– Normal faults– Reverse faults

• Strike-slip faults

Earthquakes : Seismic waves • The pattern of "ups" and

"downs" recorded around the earthquake epicenter will indicate whether the fault was a, reverse, normal, or strike slip.

XX

Distant forces cause a gradual build up of stress in the earth over tens or hundreds or thousands of years, slowly distorting the earth underneath our feet. Eventually, a pre-existing weakness in the earth--called a fault or a fault zone--can not resist the strain any longer and fails catastrophically.

Elastic Rebound Theory

What is an earthquake?What is the role of a model in science?

Calv

in a

nd H

obbe

s by

Bill

Watt

erso

n

B

C

EQ Machine - Lite

Top ViewBulk of the Plate

Edge of the Plate

Elastic Properties of Earth Materials Plate has Constant

Velocity Here of 1cm/year

Seismic MomentMo = fault length x fault width x displacement x rigidity

Visualizing magnitude with the model

B

Moment Magnitude = Mw = log Mo/1.5 – 10.7

Where is the Fault line? Map of Homes on Fault Line

Seismic Risk Assessment

• Earthquake Prediction (?): Numerous factors have been proposed as possible precursory signals that an earthquake is imminent including changes in low magnitude seismic activity in the weeks and months preceding a major quake, changes to groundwater levels, radon and other gases in groundwater wells, changes in the electrical resistivity of the crust (related to changes in groundwater distribution in rock as it begins forming microcracks immediately prior to an earthquake, changes in seismic wave velocity in the crust surrounding a fault that is beginning to fail prior to an earthquake, even strange behavior by animals just prior to a major earthquake. To date, no predictive factor or group of factors has been found to allow the prediction of an imminent earthquake.

• Earthquake Probability: Seismologists are, however, able to estimate the probability of an earthquake of a given size occurring in a given period of years on a particular segment of a fault. Probability estimates utilize such information as the past history of earthquakes on the fault (size and average time between), magnitude and age of the most recent large earthquake (and the amount of stress released), rate of stress buildup in the plate boundary region based on the velocity of relative plate motion and regular monitoring of elastic strain buildup through survey techniques, and estimated strength of the fault (rock strength and friction).

• While the frequency of earthquakes is much greater in areas around tectonic plate boundaries, where the stresses build up quickly, there are locales in the middle of plates, far from active faulting where stresses nevertheless build up on ancient faults potentially leading to major earthquakes (for example, the New Madrid fault zone on the Mississippi River).

• Seismic Gaps and Sequences: Segments of faults that have not had significant earthquakes (stress release) in some time are more likely to have an earthquake sooner than segments that have had more recent earthquakes.

• In Turkey, since 1939 there has been a westward progression of damaging earthquakes on segments of the North Anatolian fault. The most recent one was a 1999 earthquake that caused major damage and many deaths in the city of Izmet. Based on the sequence, the great city of Istanbul appears to be next.

• Damage Factors: - Loose, unconsolidated sediments, and especially saturated sediments experience stronger ground motions in an earthquake as compared to solid bedrock. Damage to structures is least where built on solid bedrock.- Buildings have their own natural vibration frequency, like a tuning fork, depending on their height and rigidity. Given the natural vibration frequency of the rocks or sediments upon which the building are constructed, buildings of a particular height range are most susceptible to damage in strong earthquakes. - Unconsolidated sediments may undergo liquefaction in a strong earthquake allowing buildings to sink, usually one side more than the other so that the building topples. - A "seismic bounce" causes stronger than expected ground motion at a distance from an earthquake epicenter where reflected seismic waves combine with direct-arriving seismic waves.- Strong earthquakes typically break underground gas lines leading to fires. Water lines also break making it difficult to fight the fires.- Strong earthquakes that offset the seafloor produce tsunamis, which are not normally discernible from a ship at sea with their very long wavelengths, but as theses very rapidly moving waves come into shallow water approaching the shoreline they slow greatly, getting steeper and much higher innundating low-lying coasts.- Earthquakes may also set landslides and mudslides in motion, burying whole neighborhoods.

• Earth’s Structure: Animation & Quiz• Plate convergence : USGS• Fault quiz

“A” is the

Hanging wall

Foot wall

Fault plane

Fault trace

That is CORRECT

That is Incorrect

http://www.google.com/url?sa=i&rct=j&q=P+and+S+waves&source=images&cd=&cad=rja&docid=ljWvlEPiz1a0FM&tbnid=ssPDEeOUQ4rQzM:&ved=0CAUQjRw&url=http://www.drjudywood.com/articles/DEW/&ei=XPhVUbm6IaOEygGGkIGABw&bvm=bv.44442042,d.aWc&psig=AFQjCNH9AN752V6LcrFW0Fm4x4u6usF53Q&ust=1364674995337803