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Time-Distance graph: plots the predicted arrival time of S- and P-waves as a function of distance. It can calculate time it took from epicenter to point A, to B to C and distance traveled.

S-P lag time is the time lag between S and P waves; it increases with distance from epicenter.

Earthquakes occur where there are plate boundaries; plate tectonics spread stress around; rupture along different zones can have faulting and earthquake activities.

Difference between intensity and magnitude:

Intensity: measures the damage caused by an earthquake - which in turn depends on:

* Energy of the earthquake;

* Distance from the earthquake;

* Local ground condition;

* Type of buildings.

Magnitude: measures the energy released during an earthquake.

We need amplitude and distance to know the magnitude. It's a logarithmic scale:

Increase 1 unit = 10 times greater shaking

Increase 1 unit ~ 32 times greater energy

Earthquake hazards: Buildings collapse caused by:

* Fault rupture

* Ground shaking

* Liquefaction of sediment

* Landslides

* Tsunamis = large p-waves that cause flooding, etc.

* Dam failure

* Fires - shaking break gas maines

Historical Earthquakes:

* 1811-1812 New Madrid Earthquake

* 1906 San Francisco Earthquake: M~8.1-8.2, 700 lives lost; damage mostly due to fire; greatest damage on made-land; or land that used to be marshland which tends to shake more like jello. Transform plate boundary.

* 1964 Alaskan Earthquake (Good Friday Earthquake) M~8.3-8.4; 131 lives lost; notable for large tsunami and pattern of rebuilding. Rebuilt same place where earthquake happened. Buildings destroyed, downtown collapsed. Subdivision