earthquake: shaking and trembling that results from sudden movement of part of the Earth’s crust Caused by release of energy (lithospheric plates)

OCCURS FOR MANY REASONS: ground shakes from erupting volcano collapse of a cavern impact of meteor major cause- stress that builds up and causes faulting

Elastic rebound theory: rocks that are strained past a certain point will fracture and spring back to their original shape

Depth inside the Earth at which an earthquake occurs depends upon the kind of plate boundary focus: point beneath the Earth’s surface where the rocks break or move apart Point on fault plane where 1 st movement occurs

epicenter: point on Earth’s surface directly above the focus site of most violent shaking focus

P waves (primary): move fastest back and forth waves move through solid, liquid or gas push-pull waves

S waves (secondary): travel slower move side to side travel through solids

L waves (surface): move slowest move like ripples on a pond

Blue primary waves followed by red secondary waves move outward in concentric circles from the epicenter of an earthquake off British Columbia and Washington State.

Seismograph: instrument that detects and measures seismic waves

Seismogram:seismograph’s record of waves; has wavy lines recorded on paper

Seismogram

Seismologist: scientists who study earthquakes

Tracing made by a seismograph can be used to tell how far away an earthquake’s epicenter is from the station that recorded it: Need distance from 3 different stations in order to determine location Point where all 3 circles meet is location of epicenter

Locating an Earthquake

seismograms can be used to determine strength or magnitude of energy produced by an earthquake Richter scale: measures how much energy an earthquake releases by assigning a number from 1 to 10- each is 10x’s higher

Pacific Ring of Fire: major earthquake zone that forms a ring around the Pacific Ocean

Successful earthquake prediction must correctly forecast: where it will occur when it will occur what magnitude it will be

Possible methods for prediction: detect slight tilting of ground before an earthquake natural gas seepage Microquakes (foreshocks)

Foreshocks & Aftershocks Foreshock: small earthquakes that occur prior to a major quake Aftershock: small earthquakes generated by adjustments of materials that follow a major quake.

Animal Behavior Unusual behavior prior to an earthquake event behavior of animals 2004 Indonesia Tsunami –In Thailand, elephants broke their chains and ran to a mountaintop –People survived by following animals (monkeys, elephants, dolphins) fleeing from the coast. –Very few animal corpses were found

Fault Fractures in the Earth where movement has occurred. Causes by stress

faulted rocks have two blocks: –hanging wall: block of rock above fault –foot wall: block of rock below fault

Types of Faults normal fault : formed when hanging wall moves down relative to the foot wall

reverse fault : formed when hanging wall moves up relative to the foot wall

strike-slip fault : rocks on either side of fault are moving past each other

fold : bend in the rock (rock deformed but doesn’t break) anticline: upward fold in the rock (forms ridges) syncline: downward fold in the rock (forms valleys)