EARTHQUAKES: CAUSES AND CHARACTERISTICS
Lecture 5
September 16, 2013
EARTHQUAKES: CAUSES AND CHARACTERISTICS Causes of Earthquakes Plates are part of the crust There can be long/short fractures in the crust Faults can be boundaries between plates Usually fractures are in the middle Faults are classified by the way the rocks slide on either side: o Normal faults: slips below the normal level of land o Revers/Thrust faults: move up above the normal level of land o Strike-slip faults: move horizontally (not up or down) The Elastic Rebound Theory Made by Henry F. Reid (1910) Earthquakes involve an “elastic rebound” of previously stored elastic stress Plates bend and it creates stress/strain Stress and strain are released during the earthquake when the plate breaks Tectonic Environments of Faults Earthquakes and faults are associated with plate boundaries Strike/slip faults are associated with transform boundaries (tectonic boundaries) Revers/thrust faults are associated with convergent boundaries (areas with huge earthquakes – plates coming together) Normal faults are associated with divergent boundaries (plates going away from each other) Earthquake Waves (Only know this slide – not what is in the textbook) Two types of waves Body Waves Primary Waves: o Push and pull the rock they go through o Happen in the crust not on the surface Secondary Waves: o Slower o Can change the structure of the rock they go through o In the upper crust Surface Waves Slower than body waves Do more damage in earthquakes Love Waves: shake the ground
Lecture 5
September 16, 2013
Rayleigh Waves: displace the ground
Seismograph Important to know the time between P and S waves Can use it to time the intervals between the arrivals of P and S waves Can use this info to locate the epicenter of the earthquake Earthquake Size and Characteristics Intensity: Modified Mercalli Intensity Scale Based on what people feel (shaking) and severity of damage About human consequences Magnitude: Richter Scale Magnitude characterizes the size of the earthquake Uses motion of the earthquake Amount of energy released during the earthquake Not human consequences/damages Historic Earthquakes Earthquake in Chile had the highest score on Richter Scale: 9.5 iClicker Questions: 1. Will California eventually fall off the ocean? a. Yes b. No (a continental plate cannot go under an oceanic plate) c. It depends on… d. I don’t know 2. If you find a well-exposed fault that moved before seismographs were available, you can infer the approximate magnitude of earthquake by measuring the ___________. a. Largest size tree snapped off by the shaking b. Average size of the largest rocks moved in the earthquake c. Strength of the rocks that the earthquake managed to break d. Total length of fault break during the event
September 16, 2013
EARTHQUAKES: CAUSES AND CHARACTERISTICS Causes of Earthquakes Plates are part of the crust There can be long/short fractures in the crust Faults can be boundaries between plates Usually fractures are in the middle Faults are classified by the way the rocks slide on either side: o Normal faults: slips below the normal level of land o Revers/Thrust faults: move up above the normal level of land o Strike-slip faults: move horizontally (not up or down) The Elastic Rebound Theory Made by Henry F. Reid (1910) Earthquakes involve an “elastic rebound” of previously stored elastic stress Plates bend and it creates stress/strain Stress and strain are released during the earthquake when the plate breaks Tectonic Environments of Faults Earthquakes and faults are associated with plate boundaries Strike/slip faults are associated with transform boundaries (tectonic boundaries) Revers/thrust faults are associated with convergent boundaries (areas with huge earthquakes – plates coming together) Normal faults are associated with divergent boundaries (plates going away from each other) Earthquake Waves (Only know this slide – not what is in the textbook) Two types of waves Body Waves Primary Waves: o Push and pull the rock they go through o Happen in the crust not on the surface Secondary Waves: o Slower o Can change the structure of the rock they go through o In the upper crust Surface Waves Slower than body waves Do more damage in earthquakes Love Waves: shake the ground
Lecture 5
September 16, 2013
Rayleigh Waves: displace the ground
Seismograph Important to know the time between P and S waves Can use it to time the intervals between the arrivals of P and S waves Can use this info to locate the epicenter of the earthquake Earthquake Size and Characteristics Intensity: Modified Mercalli Intensity Scale Based on what people feel (shaking) and severity of damage About human consequences Magnitude: Richter Scale Magnitude characterizes the size of the earthquake Uses motion of the earthquake Amount of energy released during the earthquake Not human consequences/damages Historic Earthquakes Earthquake in Chile had the highest score on Richter Scale: 9.5 iClicker Questions: 1. Will California eventually fall off the ocean? a. Yes b. No (a continental plate cannot go under an oceanic plate) c. It depends on… d. I don’t know 2. If you find a well-exposed fault that moved before seismographs were available, you can infer the approximate magnitude of earthquake by measuring the ___________. a. Largest size tree snapped off by the shaking b. Average size of the largest rocks moved in the earthquake c. Strength of the rocks that the earthquake managed to break d. Total length of fault break during the event
