Can vary from county to country Modified Mercalli Intensity Maps show where the

Can vary from county to country modified mercalli

This preview shows page 53 - 68 out of 124 pages.

• Can vary from county to country Modified Mercalli Intensity Maps show where the damage is most severe • Based on questionnaires sent to residents, newspaper articles, and reports from assessment teams • Recently, USGS has used the internet to help gather data more quickly Earthquake Intensity
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Intensity: MMIS M odified M ercalli I ntensity S cale Subjective reconstruct from historical records Effects of earthquake on people/structures
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Abbreviated Modified Mercalli Intensity Scale
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Seismic Intensity Map, Loma Prieta 1989 Note that intensity decreases with distance from the epicenter of the earthquake
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Shake Maps use high-quality seismograph data to show areas of intense shaking Useful in crucial minutes after an earthquake o Show emergency personnel where greatest damage likely occurred o Locate areas of possible damaged gas lines and other utilities Earthquake Intensity Real-Time Instrumental Intensity of Shaking
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Focus is the place within the Earth where the earthquake starts Depth of earthquake influences the amount of shaking Deeper earthquakes cause less shaking at the surface Lose much of the energy before reaching surface • Loss of energy is called attenuation Depth of Earthquake Focus
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Earthquake distribution Map showing global distribution of moderate earthquakes (1963-1988). Notice that most earthquakes occur along plate boundaries (shaded area)
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Distribution of 14,229 earthquakes with magnitudes > 5 for the time period 1980 – 1990. Notice that most earthquakes occur along plate boundaries Earthquake Belts: Locations
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Significant Earthquakes in the US
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Colors show the levels of horizontal shaking that have a 1- in-10 chance of being exceeded in a 50 year period U.S. Geological Survey Shaking Hazard Map Charleston, S.C. 1886 Earthquake Belts: Location New Madrid, MO 1812
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Subduction Zones Site of the largest earthquakes – Megathrust earthquakes Example: Cascade Mountains Convergence between a continental and oceanic plates Example: Aleutian Islands Convergence between two oceanic plates Transform Fault Boundaries Example: San Andreas Fault in California, Loma Prieta earthquake Boundary between North American and Pacific plates Plate Boundary Earthquakes
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Earthquakes that occur within plates Example: New Madrid seismic zone (near St. Louis, MO) Historic earthquakes similar in magnitude to West Coast quakes Earthquakes in Oklahoma and Southern Kansas Intraplate Earthquakes Often smaller in magnitude than plate boundary quakes, but Can cause considerable damage due to lack of preparedness Can travel greater distances through stronger continental rocks
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2010 Chile megathrust earthquake - biggest-earthquakes-110412.html
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Earthquake Hazard “Earthquakes don’t kill, buildings do”
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Science helps us predict hazards Study of precursor events careful analysis of available scientific data Knowing hazard risks can help people make decisions
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