Earthquake HazardsEarthquake HazardsKey ideas:Key ideas:

The amount of damage an earthquake causes The amount of damage an earthquake causes depends on its magnitude, and where it occurs.depends on its magnitude, and where it occurs.Safe building practices can limit loss of life and Safe building practices can limit loss of life and

damage to property.damage to property.

Damage from EarthquakesDamage from Earthquakes

Earthquakes have a tremendous Earthquakes have a tremendous destructive power; they strike quickly, destructive power; they strike quickly, and many, many times unexpectedly. and many, many times unexpectedly. Within seconds or minutes thousands of Within seconds or minutes thousands of people can die, and buildings turn into people can die, and buildings turn into piles of debris. piles of debris.

Most earthquakes occur at the boundaries Most earthquakes occur at the boundaries of plate tectonics, or faults. (Faults are of plate tectonics, or faults. (Faults are planes along which masses of rocks are planes along which masses of rocks are displaced) displaced)

Damage from EarthquakesDamage from Earthquakes

An earthquake can destroy any man An earthquake can destroy any man made structure (buildings, bridges, made structure (buildings, bridges, roads, etc) in several ways:roads, etc) in several ways:

1.1. Ground shakingGround shaking

2.2. Aftershocks and fireAftershocks and fire

3.3. TsunamisTsunamis

Ground ShakingGround Shaking

Ground shakingGround shaking is caused by the P is caused by the P waves (the ground is shook side waves (the ground is shook side to side) and the S waves (the to side) and the S waves (the ground is shook up and down). ground is shook up and down). Most buildings can withstand up Most buildings can withstand up and down shaking, but few will and down shaking, but few will resist to side to side vibration. resist to side to side vibration.

Ground ShakingGround Shaking Buildings that are built on solid rock have better Buildings that are built on solid rock have better

chances to remain intact than buildings that are chances to remain intact than buildings that are built on soft rocks. built on soft rocks. Soft rocks or loose soil can Soft rocks or loose soil can temporarily take some of the properties of a temporarily take some of the properties of a liquid during an earthquake. This is called liquid during an earthquake. This is called liquefaction. liquefaction.

For example, San Francisco’s Marina district sits For example, San Francisco’s Marina district sits on a landfill which was used to extend the city on a landfill which was used to extend the city into San Francisco Bay. In the 1989 Loma Prieta into San Francisco Bay. In the 1989 Loma Prieta earthquake this landfill liquefied, shaking earthquake this landfill liquefied, shaking buildings off their foundations. Liquefaction buildings off their foundations. Liquefaction caused great loses in Turkey (1999), Alaska caused great loses in Turkey (1999), Alaska (1964) Mexico City (1985).(1964) Mexico City (1985).

Ground ShakingGround Shaking

Ground ShakingGround Shaking

Aftershocks and FireAftershocks and Fire

Most earthquakes are followed by a series Most earthquakes are followed by a series of smaller ones, originating close to the of smaller ones, originating close to the focus of the large earthquake. These focus of the large earthquake. These smaller earthquakes are called smaller earthquakes are called aftershocks. aftershocks. Although the magnitude of Although the magnitude of these aftershocks is considerably smaller these aftershocks is considerably smaller than the initial earthquake, many still than the initial earthquake, many still standing but weakened buildings might standing but weakened buildings might collapse during the aftershocks.. collapse during the aftershocks..

Fires Fires

Imagine that an earthquake affects a Imagine that an earthquake affects a heavily populated area, with miles and heavily populated area, with miles and miles of gas pipes running under the miles of gas pipes running under the ground. The ground movement breaks ground. The ground movement breaks apart the gas lines, and a spark is enough apart the gas lines, and a spark is enough to start a devastating fire. to start a devastating fire.

After the 1906 San Francisco earthquake After the 1906 San Francisco earthquake the fires destroyed about 3000 buildings the fires destroyed about 3000 buildings and burned about 11 square Km of the and burned about 11 square Km of the city.city.

Northridge 1994, the fire after the Northridge 1994, the fire after the quakequake

San Francisco 1906San Francisco 1906

TsunamisTsunamis

TsunamisTsunamis are huge waves created are huge waves created by a displacement of water - a by a displacement of water - a landslide, volcanic eruption, or landslide, volcanic eruption, or slippage of the boundary between slippage of the boundary between two of the earth's tectonic plates – two of the earth's tectonic plates – thick slabs of rock that carry the thick slabs of rock that carry the Earth's continents and seas on an Earth's continents and seas on an underground ocean of much hotter, underground ocean of much hotter, semi-solid material.semi-solid material.

TsunamisTsunamis

Tsunamis can travel up to 600 mph Tsunamis can travel up to 600 mph (965 km/hour, or 521 knots) at the (965 km/hour, or 521 knots) at the deepest point of the water, but slow deepest point of the water, but slow down as they get near the shore, down as they get near the shore, eventually hitting the shore at 30 to 40 eventually hitting the shore at 30 to 40 mph (48 to 64 km/h or 26 to 35 knots). mph (48 to 64 km/h or 26 to 35 knots). The energy of the wave's speed is The energy of the wave's speed is transferred to height and sheer force transferred to height and sheer force as it approaches the shore.as it approaches the shore.

TsunamiTsunami

Earthquakes FactsEarthquakes Facts

On of the most destructive On of the most destructive earthquakes recorded since 1900 earthquakes recorded since 1900 occurred on July 27, 1976, in occurred on July 27, 1976, in Tangshan, China, when the official Tangshan, China, when the official death count reach 255,000 for a 7.5 death count reach 255,000 for a 7.5 magnitude quake. Estimated death magnitude quake. Estimated death counts, however, reached as high as counts, however, reached as high as 655,000.655,000.

Earthquake FactsEarthquake Facts

The highest toll for an earthquake-tsunami The highest toll for an earthquake-tsunami combination since 1900 took place on combination since 1900 took place on December 28, 1908, when a 7.2 December 28, 1908, when a 7.2 magnitude quake struck Messina, Italy, magnitude quake struck Messina, Italy, killing an estimated 70,000 to 100,000 killing an estimated 70,000 to 100,000 people.people.

The deadliest earthquake ever recorded is The deadliest earthquake ever recorded is believed to have occurred on January 23, believed to have occurred on January 23, 1556, in Shansi, China, killing 830,000 1556, in Shansi, China, killing 830,000 people.people.

Earthquake factsEarthquake facts

The worst tsunami in recent history The worst tsunami in recent history followed the August 27, 1883, the followed the August 27, 1883, the eruption of the volcano Krakatau. eruption of the volcano Krakatau. The resulting wave swept over the The resulting wave swept over the Indonesian islands of Java and Indonesian islands of Java and Sumatra, ultimately killing 36,000 Sumatra, ultimately killing 36,000 people.people.

SourcesSources

U.S. Geological Survey - U.S. Geological Survey - www.usgs.gov

Pacific Tsunami Warning Center - Pacific Tsunami Warning Center - www.prh.noaa.gov/ptwc

University of Oregon Seismology University of Oregon Seismology Dept - Dept - www.geophys.washington.edu

http://earthquake.usgs.gov/http://earthquake.usgs.gov/eqcenter/recenteqsus/eqcenter/recenteqsus/

Earthquake RiskEarthquake Risk

Where do major earthquakes occur? What Where do major earthquakes occur? What areas in the world are at risk?areas in the world are at risk?

To answer this question, let’s remember that To answer this question, let’s remember that earthquakes are closely related to earthquakes are closely related to movement of plate tectonics or movement movement of plate tectonics or movement of packs of rocks along faults. of packs of rocks along faults.

Hence, earthquakes happen everywhere in Hence, earthquakes happen everywhere in the world where these conditions are met.the world where these conditions are met.

Earthquake risk in the USEarthquake risk in the US

Earthquake risk in the USEarthquake risk in the US

The west coast of the United States The west coast of the United States is the most tectonically active.is the most tectonically active.

Notice that California has the highest Notice that California has the highest risk for major earthquakes to risk for major earthquakes to happen. Los Angeles and San happen. Los Angeles and San Francisco, two of the largest cities in Francisco, two of the largest cities in the US are close to one of the most the US are close to one of the most active faults in the world: the San active faults in the world: the San Andreas Fault. Andreas Fault.

Europe’s seismic mapEurope’s seismic map

South Asia’s seismic mapSouth Asia’s seismic map