Name of School

Date

Earthquakes and Seismology

Plate Tectonics

A Century of Earthquakes: 1906-2006

Global Seismographic Network

2006 Earthquakes > M5.5

2006 Earthquakes > M5.5 in the world

How Many?

Earthquake Magnitude and Equivalent Energy Comparisons

Source: http://www.iris.edu/edu/onepagers/no3.pdf

Earthquakes generate Seismic Waves that travel around the globe and tell us about the Earth’s interior.

Simple Seismometer

A simple way to measure shaking from earthquakes.

To see it in action, watch this 14 sec videohttp://www.youtube.com/watch?v=DX5VXGmdnAg&NR=1

What is an Earthquake?

Earthquake: The sudden release of elastic energy by fracture over some area of the earth.

What is an Earthquake?

Earthquake: The sudden release of elastic energy by fracture over some area of the earth.

Earthquake: The sudden slip on a fault (release of elastic energy), and the resulting ground shaking and radiated seismic energy caused by the slip.

Fault: A fracture (crack) in the earth, where the two sides move past each other and the relative motion is parallel to the fracture.

Typical Plate Boundaries

Plate Boundaries& earthquakes

Types of Faults

A fence built over a fault…

1906 San Francisco Earthquake

Fence Offset

Offset Stream Channels in Central California

Types of Seismic Waves P-wave:

Primary Wave. Compressional wave, like a Slinky© being pushed and pulled.

S-wave: Secondary Wave. This is a shear wave where

particles move perpendicular to the travel direction of the wave.

Surface Waves: Both Love and Rayleigh Waves. Only shallow

particles are disturbed. Love waves are sideways, Rayleigh are vertical (like ocean waves).

Types of Seismic Waves

Types of Seismic Waves

Seismographs

Horizontal Vertical

Distance to quake epicenter

P

S

L

Note:P-wave firstS-wave secondSurface waves last

Time lag between p and s-wave arrival is called t.

Fig 3.22

Ts=23sTp=14s

Maximum Amplitude = 540 mm

Locating Earthquakes

Fig. 3.23

Locating Earthquakes

Locating Earthquakes

Earthquake SizeRichter Magnitude:

Relative Size of an Earthquake(based on seismograph

shaking)

Seismic Moment/Moment Magnitude: Absolute Size of an Earthquake

(based on energy released)

Modified Mercalli Intensity:How much I’m shakin’(based on talking to people)

Calculating Richter MagnitudeA.K.A Local Magnitude

ML = log10A - log10Ao

A is the amplitude of the s-wave measured at given stationAo is the amplitude of a MR=0 event at the same distance

PS

Log of the Amplitude for a Magnitude 0 Earthquake

M = 4

M = 0

Earthquake: The sudden slip on a fault (release of elastic energy), and the resulting ground shaking and radiated seismic energy caused by the slip.

Aki’s Seismic Moment Formula

Mo = s A

Where:

is the shear modulus.S is the average slip on the faulted area.A is the area of the fault plane over which slip has occurred.

Shear modulus ( can just be thought of as the strength of the faulted material

Modified Mercalli Intensity

Based on response of humans and structures

I (not felt except by few)

XII (total destruction)

Still useful for comparison with older earthquakes for which there were no instrument records

Earthquake Info on the Internet

http://earthquakes.usgs.gov/

Earthquake Info on the Internet

http://earthquakes.usgs.gov/eqcenter/dyfi.php

Did You Feel It???

Go online and tell us!

Earthquake Info on the Internethttp://www.data.scec.org/recenteqs.html

Southern California with

Faults & the Big Bend

Southern California from Space(1)

Southern California from SpaceWith a Few Major Faults

Historical Earthquakes (1800-1850)Historical Earthquakes (1850-1900)Historical Earthquakes (1900-1950)Historical Earthquakes (1950-2004)Historical Earthquakes (1000-1800)

Smith and Sandwell, 2006

Thank You for Your Attention

Questions?