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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

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