Earthquakes

Given information on Earthquakes, you will be able to describe, in writing: a) what an earthquake is; b) what the elastic rebound theory is; c) how earthquakes are measured; d) how earthquakes are related to plate tectonic theory; e) hazards associated with earthquakes; and f) the significance of studying earthquakes. Objectives

Earthquakes Definition: An earthquake (also known as a tremor or temblor) is the result of a sudden release of energy in the Earth's crust that creates seismic waves.Earthcrust seismic waves

Earthquakes Elastic Rebound Theory explanation for how energy is spread during earthquakes plates/blocks of earth shift on opposite sides of a fault these are subjected to force (Time 1) they accumulate energy (Time 2) they slowly deform until their internal strength is exceeded a sudden movement occurs along the fault accumulated energy is released rocks snap back to their original undeformed shape (Time 3)

Earthquakes Measurement 1. Magnitude scale a) measures energy released; b) an earthquake one number higher is approximately 30 times more powerful (e.g. a 7.0 vs. a 6.0); (the scale is logarithmic) d) an earthquake one number higher produces approximately 10 times more ground shaking e) examples = Moment Magnitude, Richter

Earthquakes Measurement (cont.) 2. Mercalli Intensity scale a) measures intensity or damage of an earthquake; b) quantifies the effects of an earthquake on the Earth's surface, humans, objects of nature, and man-made structures d) scale ranges from I through XII, with I denoting a weak earthquake and XII one that causes almost complete destruction e) based on the amount of resulting physical damage received f) data is gathered from individuals who have experienced the quake

Earthquakes Plate Tectonics Earthquakes are NOT randomly distributed across the globe They are concentrated along narrow zones Most earthquakes (~80% or more) occur along plate boundaries Interior of plates are mostly earthquake free Earthquakes define plate boundaries Some also occur at Hot Spots

Earthquakes Hazards 1.Ground motion 2.Liquefaction 3.Landslides & mass wasting 4.Tsunamis

Ground motion simulation map from the 1906 SF Earthquake Ground Motion

Liquefaction

Landslides & Mass Wasting

Tsunamis

Earthquakes Significance It is important to study earthquakes due to the loss of life and damage to property they can cause Human population continues to grow and many cities are cited along plate boundaries Education is the key to being prepared for earthquakes

Summary Earthquakes occur due to the elastic rebound theory Earthquakes are measured using the magnitude scale Earthquakes occur along plate boundaries Earthquakes cause ground motion, tsunamis, mass wasting, and liquefaction Earthquake hazards may cause loss of life and damage to property