Earthquakes I used to sleep nude - until the earthquake. --Alyssa Milano

Where?

Where?

--Mainly at plate boundaries –Convergent and transform, usually –Sometimes in the middle of a plate

How?

Pressure builds up Rocks break when their shear strength is overcome Rock layer snap back with elastic rebound

How? Rocks move at a fault

How? Rocks move at a fault This motion makes earthquake waves

The epicenter is over the focus

Earthquake waves 3 types of waves: (see diagram, p G-128)

Earthquake waves 3 types of waves: primary (P) secondary (S) and surface (L)

Earthquake waves 3 types of waves: primary (P) secondary (S) and surface (L) L waves cause most of the damage. S and P waves tell us about the interior of the Earth.

Secondary waves Direction Called Barrier Velocity

Secondary waves Direction Called Barrier Velocity Side to side motion

Secondary waves Direction Called Barrier Velocity Side to side motion Shear waves

Secondary waves Direction Called Barrier Velocity Side to side motion Shear Stops at solid/liquid barrier

Secondary waves Direction Called Barrier Velocity Side to side motion Shear Stops at solid/liquid barrier Slower

Secondary waves Direction Called Barrier Velocity Side to side motion Shear Stops at solid/liquid barrier Slower

Primary waves Direction Called Barrier Velocity

Primary waves Direction Called Barrier Velocity Parallel to direction of travel

Primary waves Direction Called Barrier Velocity Parallel to direction of travel Pressure waves

Primary waves Direction Called Barrier Velocity Parallel to direction of travel Pressure waves Passes solid/liquid barrier

Primary waves Direction Called Barrier Velocity Parallel to direction of travel Pressure waves Passes solid/liquid barrier Phaster than S waves

Primary waves Direction Called Barrier Velocity Parallel to direction of travel Pressure waves Passes solid/liquid barrier Phaster than S waves

Seismographs flash/8_3.swf

Seismographs The pen is steady, paper is pulled under it. If the paper shakes, the line swings P waves reach the seismograph first The time lag before the S waves reach it tell you how far away the earthquake was

EARTHQUAKE!

P waves lead S waves by 2:30 in Denver

Epicenter is 2000 km from Denver

P waves lead S waves by 1:05 in Seattle

Epicenter is 800 km from Seattle

P waves lead S waves by 1:15 in LA

Epicenter is 900 km from LA

Epicenter is in SE Oregon!

Seismic evidence explains the different layers of the Earth.

S waves bend, but don’t penetrate the outer core

The outer core must be liquid!

S waves bend, but don’t penetrate the outer core The amount of bending indicates density

P waves penetrate the outer core

They bend as they cross layers

How big was this earthquake? Two observations geoscientists make about earthquakes. Magnitude and intensity

Magnitude Measured on the Richter scale Indicates energy released Log scale: --A magnitude 4 quake has 10 times the energy of magnitude 3.

Intensity Measured on the Mercalli scale Indicates what is felt From I to XII --Intensity III can barely be felt, --Intensity VIII knocks down buildings

Earthquake Risk Small earthquakes are more common than large ones Plate boundaries are at greatest risk.

Earthquake Hazards 1) 2) 3) 4) 5) 6) 7)

Earthquake Hazards 1)Buildings fall down 2)Fires start 3)Landslides occur 4)Tsunami are triggered 5)Pipelines break 6)Power lines fall/break 7)Roads and bridges are damaged