GEOL 2207 Lecture : Earthquake Cycle.docx
Document Summary
Inactive period where stress builds in the fault. Period of small earthquakes where the stress begins to release, causing strain. Foreshocks occur prior to a major release of stress. Release of stress after a major quake. However not all at risk areas are near plate boundaries. Destructive, shallow focus quakes away from plate margins less common. Strain accumulation not directly related to plate movements. Associated with ancient geological structures: pre-existing faults, zones of weakness. We can trigger earthquakes: when we pump fluids underground, colorado pumping radioactive water into ground. Liquid waste disposals importance of fluids. Pumping of oil and gas and injections of fluids in gas bearing rocks. The weight from water reservoirs (loading water behind dam) Nuclear explosions can cause the release of stress along existing faults. Shivajisagar reservoir (india: low seismicity area, eq swarms started as reservoir started to fill in 1962, m 6. 5 quake close to dam in 1967 killed 200.
