Earthquakes

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 1st 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 3 kinds of wave motions: 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

Examine P and S waves moving through Earth's interior.

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

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

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 ~30x’s higher

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

Indian Ocean Earthquake December 26, 2004

Examine a map showing earthquake risks.

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

Possible methods for prediction: microquakes behavior of animals detect slight tilting of ground before an earthquake natural gas seepage