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 origin
Based 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 EQ
Chile Earthquake
• www.usgs.gov
Magnitude scale
Earthquakes Waves
• Body Waves
(P waves and S Waves)
• Surface Waves
( Rayleigh and Love Waves)
3 Components seismograph
P-S Waves
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
• Convergent
Example 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 Prediction
Foreshocks
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