Magnitude 8.0 San Francisco Earthquake April 18, 1906

Earthquakes & Tsunamis

Magnitude 7.0 HAITI EARTHQUAKEMagnitude 7.0 HAITI EARTHQUAKE January 12, 2010 January 12, 2010

Sumatra TsunamiDecember 25, 2004

Key Questions

• What is an earthquake?

• Where do earthquakes most frequently occur?

• What is earthquake magnitude?

• What is the connection between earthquakes and faulting (the earthquake cycle)?

• How do earthquakes produce tsunamis?

• How best to mitigate earthquake damage?

Earthquake Vocabulary

• Earthquake: a sudden release of elastic energy stored in the Earth, caused by slip on a fault. The elastic energy propagates as seismic waves.

• Fault: A surface of discontinuity separating two rock masses, with relative motion tangent to the surface.

• Focus: Point on the fault where the seismic waves originate.

• Epicenter: Point on Earth’s surface above the focus.

• Magnitude: Size of an earthquake, measured by seismic wave amplitude.

• Seismicity: Earthquake location in space and time.

• Seismometer: Instrument for measuring seismic wave ground motion.

The Earthquake Cycle

IncreasingSeismicEnergyRelease

Compression waves

Shear waves

Seismic surface waves

These waves do most of the damage to buildings, etc.

www.iris.edu

Seismicity of the Earth @ 11AM July 13, 2015

www.iris.edu

San Andreas Fault Zone: North American-Pacific Plate Boundary Fault

Right-lateral strike slip motion

Subduction Zone “Mega-Thrust” Earthquakes

Tsunami Generation Mechanism

Fukushima (Sendai) Tsunami Propagation

Fukushima tsunami advancing over agricultural land

The earthquake activity in Nepal is caused by the ongoing continent-continent collision between India and Asia. That collision has produced the Himalaya Mountains and the Tibetan Plateau.

The motion of India into Asia is essentially perpendicular to the Himalaya Mountains in Nepal. So thrust faulting earthquakes are the most common kind of earthquake in the central Himalayan region.

Magnitude 7.8 NEPAL EarthquakeMagnitude 7.8 NEPAL EarthquakeApril 25, 2015 April 25, 2015

Himalayan Front: A Giant Seismic Gap Waiting to Slip?

May 22, 1960 Chilean Earthquake: Largest Seismic Event in History

Tsunami

21 m slip

Easter Is.

Earthquake Response Drills

Earthquake Damage Mitigation: Construction

Good

Bad

Fair

Awful

Tsunami Preparedness

Detection

Horizontal Evacuation

Warning Vertical Evacuation