earthquakes

Earthquakes

Chapter 7

Web Sites about Earthquakes

• www.iris.edu• http://earthquake.usgs.gov/

For Fun• http://earthquake.usgs.gov/learn/facts.php

Information We Need from Earthquakes (EQ)

• EPICENTER (Latitude, Longitude)• FOCUS ( Hypocenter ) (Depth of the EQ)• How Big it was ? How much Energy? (Mercalli intensity vs Richter Magnitude) • What Kind it was? What type of Fault• How Long it was ?

Epicenter vs. Hypocenter (Focus)

Mercalli Intensity Scale vs Richter Magnitude

• Mercalli Intensity is measured by means of the degree of damage to structures of human originBased on (Isoseismal Lines)

Richter Magnitude (Inhabited and Uninhabited regions)- Seismic wave amplitudes measured by a seismograph- He replace numbers by their logarithms. so instead of

using their amplitudes used the powers of the numbers

Mercalli vs Richter

Mercalli • Map of intensities with

isoseismal lines

Richter Magnitude• When a logarithmic scale

every time the magnitude goes up by 1 unit, the amplitude of the earthquake waves is increased by 10 times

• Example 4 to 5 ( 10 times )• 4 to 6 (100 times)• 4 to 7 (1000 times)

2010 Chile EQ vs Haiti EQChile Earthquake• www.usgs.gov

Magnitude scale

Earthquakes Waves

• Body Waves(P waves and S Waves) • Surface Waves ( Rayleigh and Love Waves)

P-S Waves

3 Components seismograph

Locating and Earthquake

• We need at least 3 station to estimate the epicenter of an earthquake !

• What do seismologist need arrival times for P and S waves

A simple formula is (S time – P time )x 8.2 = Distance in KM (Kilometers)

Example

Earthquakes in Plate Boundaries

• Transform California USGS today

• ConvergentExample Chile Earthquake (Nazca Plate subducting in South-America Plate)

• Divergent USGS website eq today

Wadatti-Benioff Zone

EQ prediction • Long-Term Prediction Probability • Short-term PredictionForeshocks

Earthquake Probability

How Rock and Soil Influence Earthquake Damage

• Mexico City Earthquake Example

• Liquefaction Soils behave like liquid,

Building Codes, Example Haiti Earthquake and Chile Earthquake

Tsunamis

• EQ summatra and Tsunami

Structure of Earth

Structure of Earth

• shadow Zone