GY111 Physical Geology Earthquakes and Seismic Waves Earthquake Mechanisms Brittle Mechanical Model stick slip Focal point 3D point inside the lithosphere where the seismic event occurs Epicenter projection of focal point to the map surface Seismic Energy Release Radiates from focal point P waves compressional fastest S waves shear Surface waves move only on surface slowest cause damage to structures Seismic Wave Mechanics P waves always travel faster than S waves Locating the Epicenter Requires readings from 3 seismic stations at 3 different geographic locations Seismic Moment Magnitude Richter scale is similar Measured from deflection of pen on seismograph Earthquakes Plate Tectonics Distribution of epicenters outline plate boundaries Focal Depth Deep focal point earthquakes occur only in subduction zones Only shallow focal points are found along divergent ocean ridge systems Earthquake Damage Direct destruction via surface waves Landslides and ground failure Tsunami Fires Earthquake Damage Soft sediments Poor construction Disaster Management Problems Transportation network destroyed No emergency services Power grid down Many casualties No communication Food and water supplies limited Sanitation difficult U S Seismic Risk Proximity to active fault zones Nature of bedrock Proximity of populations centers and infrastructure Building codes World Seismic Risk Exam Summary Know differences between P S and surface waves Be familiar with the stick slip theory of earthquake propagation Know how epicenters and focal points are located with seismic data Be familiar with the association of earthquake types with various plate tectonic boundaries Be familiar with the differences between wind generated ocean waves and seismic sea waves Tsunamis
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