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Chapter 6

Earthquakes

Dr. Joao Santos

Chapter 6

Earthquakes

Dr. Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

What is an Earthquake? � Earth shaking caused by a rapid release of energy.

� Due to tectonic stresses that cause rocks to break.

� Energy moves outward as an expanding sphere of waves.

� This waveform energy can be measured around the globe.

� Earthquakes destroy buildings and kill people.

� 3.5 million deaths in the last 2000 years.

� Earthquakes are common.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Seismicity � Seismicity (earthquake activity) occurs due to…

� Motion along a newly formed crustal fracture (or fault).

� Motion on an existing fault.

� Inflation of a magma chamber.

� Volcanic eruption.

� Giant landslides.

� Meteorite impacts.

� Nuclear detonations.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Earthquake Concepts � Hypocenter (or focus) - The spot within the Earth where

earthquake waves originate.

� Usually occurs on a fault surface.

� Earthquake waves expand outward from the hypocenter.

� Epicenter – Land surface above the hypocenter.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Faults and Earthquakes � Most earthquakes occur along faults.

� Common crustal fractures that move rock masses.

� The amount of movement is termed displacement.

� Displacement is also called offset, or slip.

� Markers reveal the

amount of offset.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

� Faults are like planar breaks in blocks of crust.

� Most faults slope (although some are vertical).

� On a sloping fault, crustal blocks are classified as:

� Footwall (block below the fault).

� Hanging wall (block above the fault).

Faults and Fault Motion

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Fault Types � Fault type based on relative block motion.

� Normal fault

�Hanging wall moves down relative to footwall.

�Result from extension (stretching).

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Fault Types � Fault type based on relative block motion.

� Reverse fault

�Hanging wall moves up relative to footwall.

�Results from compression (squeezing or shortening).

�Slope (dip) of fault is steep.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Fault Types � Fault type based on relative block motion.

� Thrust fault

�Special kind of reverse fault.

�Slope (dip) of fault surface is not steep.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Fault Types � Fault type based on relative block motion.

� Strike-slip fault

�Blocks slide laterally past one another.

�No vertical block motion.

�Fault surface is nearly vertical.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Fault Types � Fault type based on relative block motion.

� Oblique-slip fault

�A combination of dip-slip and strike-slip displacement.

�Most faults display an oblique-slip character.

�Pure dip-slip or strike-slip faults are rare.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Fault Initiation � Tectonic forces add stress to unbroken rocks.

� The rock deforms slightly (elastic strain).

� Continued stress will cause growth of cracks.

� Eventually, cracks grow to the point of failure.

� When the rock breaks, elastic strain transforms into brittle deformation, releasing earthquake energy.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Fault Motion � Faults move in jumps.

� Once movement starts, it quickly stops due to friction.

� Eventually, strain builds up again causing failure.

� This behavior is termed stick-slip behavior.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Seismic Waves � Body waves – Pass through Earth’s interior.

� Compressional, or primary (P), waves

�Push-pull (compress and expand) motion.

�Travel through solids, liquids, and gases.

�Fastest.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Seismic Waves � Body waves – Pass through Earth’s interior.

� Shear, or secondary (S), waves

�“Shaking" motion.

�Travel only through solids, not liquids.

�Slower.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Seismic Waves � Surface Waves – Travel along Earth’s surface.

� Love waves – S waves intersecting the surface.

�Move back and forth like a writhing snake.

� Rayleigh waves – P waves intersecting the surface.

�Move like ripples on a pond.

� These waves are the slowest and most destructive.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Seismology � Seismology is the study of earthquake waves.

� Seismographs – Instruments that record seismicity.

� Worldwide, they detect earthquakes anywhere on Earth.

� Seismology reveals size and location of earthquakes.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

� Measure wave arrivals and magnitude of motion.

� Straight line = background.

� 1st wave causes frame to sink (pen goes up).

� Next vibration causes opposite motion.

Seismographs

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Seismograph Operation � Waves always arrive in sequence.

� P waves first

� S waves second

� Surface waves last.

� Wave arrivals are captured by the seismograph.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Locating an Epicenter � p and s waves travel at different velocities.

� 1st arrivals of p and s waves vary with distance.

� A travel-time graph plots the distance of each station to the epicenter.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Locating an Epicenter � Data from 3 stations can pinpoint the epicenter.

� A circle is drawn around each station.

�The radius is equal to the distance to epicenter.

�Circles around 3 or more stations will intersect.

� The point of intersection is the epicenter.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Earthquake Size � Size is described by either intensity or magnitude.

� Mercalli intensity scale - Degree of shaking damage.

� Roman numerals assigned to different levels of damage.

� Damage occurs in zones.

� Damage diminishes in

intensity with distance.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Earthquake Size

� Magnitude – The amount of energy released.

� Maximum seismogram motion.

� Several magnitude scales.

� Richter.

� Moment.

� Magnitude scales are

logarithmic.

� Increases of 1 unit = 10 fold

increase in ground motion.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Measuring Earthquake Size

� Earthquake energy release can be calculated.

� M6.0 – Energy of the Hiroshima bomb.

� M8.9 – Annual energy released by all other earthquakes.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Measuring Earthquake Size � Small earthquakes are frequent.

� ~100,000 magnitude 3 / year.

� Large earthquakes are rare.

� 32 magnitude 7 earthquakes / year.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Earthquake Occurrence � Earthquakes linked to plate tectonic boundaries.

� Shallow – Divergent and transform boundaries.

� Intermediate and deep – Convergent boundaries.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Earthquake Focal Depths � Shallow – 0-20 km.

� Along the mid-ocean ridge.

� Transform boundaries.

� Shallow part of trenches.

� Continental crust.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Earthquake Focal Depths � Intermediate and deep earthquakes occur along the

subduction trace, the Benioff-Wadati zone.

� Intermediate – 20-300 km - Downgoing plate still brittle.

� Deep - 300-670 km - Mineral transformations?

� Earthquakes rare below

670 km (mantle is ductile).

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Convergent Boundaries � Cities near subduction zones have frequent earthquakes.

� Most are minor.

� Periodically, they are devastating.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Continental Earthquakes � Earthquakes in continental crust.

� Continental transform faults (San Andreas, Anatolian).

� Continental rifts (Basin and Range, East African Rift).

� Collision zones (Himalayas, Alps).

� Intraplate settings (ancient crustal weaknesses).

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

San Andreas Fault � The Pacific plate meets the North American plate.

� The San Andreas is a very active strike-slip fault.

� A very dangerous fault; hundreds of earthquakes per year.

� San Francisco – Destroyed in 1906.

� Loma Prieta, 1989, World Series.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Earthquake Damage � Earthquakes kill people and destroy cities.

� The damage can be heartbreaking and horrific.

� Knowledge improves odds of survival.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Earthquake Damage � Ground Shaking and Displacement

� Earthquake waves arrive in a distinct sequence.

� Different waves cause different motion.

� P waves are the 1st to arrive.

� They produce a rapid up and down motion.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Earthquake Damage � S waves arrive next (2nd).

� They produce a pronounced back and forth motion.

� This motion is usually much stronger than from P-waves.

� S waves cause extensive damage.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Earthquake Damage � Surface waves lag behind S waves.

� Love waves are the first to follow.

� Ground writhes like a snake.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Earthquake Damage � R waves are the last to arrive.

� The land surface behaves like ripples in a pond.

� These waves may last longer than others.

� Cause extensive damage.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Earthquake Damage � Severity of shaking and damage depends on…

� Magnitude (energy) of the earthquake. More = more.

� Distance from the hypocenter.

� Intensity and duration of the vibrations.

� The nature of the subsurface material.

�Bedrock transmits waves quickly = less damage

�Sediments bounce waves = amplified damage.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Earthquake Damage � Effects on buildings:

� Buildings “pancake.”

� Bridges topple.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Earthquake Damage � Effects on buildings:

� Bridge supports crush.

� Masonry walls break apart.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Earthquake Damage

� Landslides and Avalanches.

� Shaking causes slopes to fail.

� Hazardous slopes bear evidence of ancient slope failures.

� Rockslides and avalanches follow earthquakes in uplands.

� Mount St. Helens erupted via an earthquake landslide.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Earthquake Damage � Liquefaction – Waves liquefy H2O-filled sediments.

� High pore pressures force grains apart, reducing friction.

� Liquefied sediments flow as a slurry.

� Sand becomes “quicksand;” clay becomes “quickclay.”

�Sand dikes.

�Sand volcanoes.

�Contorted layering.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Liquefaction � Water saturated sediments turn into a mobile fluid.

� Land will slump and flow.

� Buildings may founder and topple over intact.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Earthquake Damage � Fire is a common hazard following earthquakes.

� Shaking topples stoves, candles, and power lines.

� Broken gas mains and fuel tanks ignite a conflagration.

� Earthquakes destroy critical infrastructure such as water, sewer, telephone, and electrical lines, as well as roads.

� Firefighters powerless.

�No road access.

�No water.

�Too many hot spots.

� Good planning is

crucial to saving lives.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Earthquake Damage � Earthquake devastation fuels disease outbreaks.

� Food, water, and medicines are scarce.

� Basic sanitation capabilities disabled.

� Hospitals damaged or destroyed.

� Health professionals overtaxed.

� There may be many decaying corpses.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Earthquake Damage � Tsunamis, or seismic sea waves (not tidal waves).

� Tsunamis result when earthquakes change the seafloor.

� Normal faulting drops the seabed; thrusting raises it.

�This displaces the entire volume of overlying water.

�A giant mound (or trough) forms on the sea surface.

�This feature may be enormous (up to a 10,000 mi2 area).

�Feature collapse creates waves that race rapidly away.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Earthquake Damage � Destructive tsunamis occur frequently - about 1/yr.

� 94 destructive tsunamis in the last 100 years.

� 51,000 victims (not including 12/26/04)

� Future tsunami disasters are inevitable.

� Growing human population in low-lying coastal areas.

� Education about tsunamis can save many lives.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Tsunami vs. Wind Waves

� Wind waves � Influence the upper ~100 m.

� Have wavelengths of several tens to hundreds of meters.

� Wave height and wavelength related to windspeed.

� Wave velocity maximum several tens of km per hour.

� Waves break in shallow water and expend all stored energy.

� Tsunami waves � Influence entire water depth

� Have wavelengths of several 10s to 100s of kilometers.

� Wave height and wavelength unaffected by windspeed.

� Wave velocity maximum several 100s of kph.

� Waves come ashore as a raised plateau of water that pours onto the land.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Tsunami Behavior � Tsunamis race at jetliner speed across the ocean.

� They may be almost imperceptible in deep water.

� Low wave height.

� Long wavelength.

� As water shallows, waves

slow from frictional drag.

� Waves grow in height,

reaching 10-15 m or more.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Tsunami � Tsunami destruction of the coast depends upon…

� Offshore bathymetry.

�Broad shallows increase amplitude but sap wave energy.

�Quick deep-to-shallow transition – Deadliest condition.

�Waves have maximum energy.

�Wave heights are modest.

�Water pours onto land as a sheet.

� Topography of shore.

�Broad lowland – Maximum damage.

�Steep rise of land – Less damage.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Tsunami Reality � The Indian Ocean Tsunami

� On December 26, 2004, a strong megathrust earthquake (M9.0+) originated in the trench to the west of N. Sumatra.

� The earthquake was the largest in 40 years.

� Displacement exceeded 15 m; rupture > 1100 km long.

� The devastating tsunami killed people in 10 countries surrounding the Indian Ocean.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

The Indian Ocean Tsunami � Killed more people than any tsunami on record.

� 227,898 were killed or missing and presumed dead.

� 1.7 million people were displaced (as of 6/4/2009).

� Record-setting death toll.

� The earthquake was

so large and the

tsunami spread fast.

� Coasts were full of

Christmas tourists.

Source: USGS Earthquake Hazards Program, Most Destructive Earthquakes http://earthquake.usgs.gov/regional/world/most_destructive.php/

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

The Indian Ocean Tsunami � Complete devastation below “run-up” elevation.

� Dense coastal development in Banda Aceh hardest hit.

� Entire communities were erased – buildings and people.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Surviving a Tsunami � Heed natural and official warnings.

� An earthquake in a coastal setting.

� Retreat of water from the shore is sign of an impending tsunami.

� Expect many waves.

� Bigger waves may be next.

� Wave arrival may last for hours.

� Abandon belongings.

� Get to high ground and stay there.

Source: Brian F. Atwater and others, 1999, Surviving a Tsunami – Lessons from Chile, Hawaii and Japan, USGS Circular 1187.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Surviving a Tsunami � Expect roads to be impassable.

� Climb a sturdy building or a tree.

� Grab something that floats.

� Expect lots of debris (sediment, wreckage, corpses).

� Expect landscape changes.

Source: Brian F. Atwater and others, 1999, Surviving a Tsunami – Lessons from Chile, Hawaii and Japan, USGS Circular 1187.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Earthquake Prediction � Prediction would help reduce catastrophic losses.

� Can we predict earthquakes? Yes and no.

� They CAN be predicted – long-term (tens to hundreds of years).

� They CANNOT be predicted - short-term (hours to months).

� Seismic hazards are mapped to assess risk.

� This information is useful for…

� Developing building codes.

� Land-use planning.

� Disaster planning.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Long-Term Earthquake Prediction � Probability of a certain magnitude earthquake occurring

on a timescale of 30 to 100 years, or more.

� Based on the premise that earthquakes are repetitive.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Long-Term Earthquake Prediction � Require determination of seismic zones, by…

� Mapping historical epicenters (after ~ 1950).

� Evidence of ancient earthquakes (before seismographs).

�Evidence of seismicity – Fault scarps, sand volcanoes, etc.

�Historical records.

� Seismic gaps, places that haven’t slipped recently.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

Long-Term Earthquake Prediction � Recurrence interval – Average time between events.

� Historical records.

� Geologic evidence – Requires radiometric dating of events.

�Sand volcanoes.

�Offset strata.

�Drowned forests.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 8: A Violent Pulse: EarthquakesChapter 8: A Violent Pulse: Earthquakes

� Goal: The location and magnitude of a large earthquake.

� Currently, we can’t reliably predict short-range events.

� Earthquakes do have precursors.

� Clustered foreshocks.

� Crustal strain.

� Stress triggering.

� And, possibly…

�Water level changes in wells.

�Gases (Rn, He) in …