CH 8 Earthquakes Produced by the rapid release of elastic energy in rock causing vibrations Elastic Rebound Theory = the rock springs back into it original place Occur at faults and plate boundaries

Vocab Focus – point within earth where earthquake originates Epicenter - point on land surface directly above the focus Aftershocks – follows the main EQ Foreshocks – EQs that precede the main earthquake Seismographs – instrument that records EQ waves Seismograms – the record made by a seismograph

Earthquake Waves Primary (P) waves Secondary (S) waves – Body wave, arrives first, fastest, pass through everything, push/pull wave Secondary (S) waves – Body wave, arrives second, slower, pass through solids only, sideways/snake wave Longitudinal (L) waves – Surface waves, arrive last, liquefy ground, do most damage, up/down wave

Locating an Earthquake Determined by the difference in arrival times between P and S waves Know the graph on page 225 Need at least 3 points to determine the location (triangulation) EQ zones – circum-Pacific belt and oceanic ridge system

Measuring Earthquakes Richter scale Based on size of largest wave Scale from 1 - 10 Moment magnitude More precise From displacement that occurs along the fault line Estimates the energy released

Earthquake Destruction Contributing factors Intensity of eq Duration of eq Foundation of building Structure/materials of building Damage prevention Reinforced concrete Shock absorbers Counter weights

Earthquake Dangers Collapsing structures #1 Fires #2 Landslides Tsunamis Move fast: 500–950 km/hr (300-600 mph) Very long wavelengths Barely noticeable in open ocean

Predicting Earthquakes Short range prediction are unsuccessful Long range forecasts are based on the idea that EQs are cyclic. Land movement Strain in rocks Radon gas emissions Strange animal behavior Volcanoes Foreshocks Seismic gap theory

Earth’s Layers Earth’s interior consists of 3 major zones (chemical composition) Crust – thin, rocky outer layer Oceanic and continental Mantle – most of earth’s volume Upper and lower mantle Core – iron/nickel alloy with extreme pressures Inner (solid) and outer (liquid)

Earth’s Interior Lithosphere Asthenosphere Moho Discontinuity Solid and rigid The crust and upper mantle Asthenosphere Softer and flows Rest of the mantle Moho Discontinuity Boundary that separates the crust from mantle Shadow zone Know differences between oceanic and continental crust