chapter4 - Click to edit Master Prediction Earthquake title...

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Click to edit Master title style 4 Earthquake Prediction and Mitigation Hyndman/Hyndman Natural Hazards and Disasters , 3 rd Edition
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Predicted Earthquake Arrives on Schedule Early afternoon February 4, 1975: officials in Haicheng, China issued warning to expect large earthquake in next two days, asked people to remain outside Prediction based on Increase in small earthquakes Rise in elevation, ground tilting near fault Changes in groundwater levels, magnetic field Strange animal behavior 7:36 pm: magnitude 7.3 earthquake struck 90% of buildings damaged or destroyed 2,014 deaths, 27,500 injuries, out of 3 million people
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Predicted Earthquake Arrives on Schedule Early 1976: officials in Tangshan, China issued forecast to expect large earthquake later that year On July 26, scientist noticed changes in electrical properties of ground, issued warning of impending earthquake Warning did not reach Tangshan before magnitude 7.6 earthquake struck Tangshan (city of 1 million) was destroyed More than 250,000 people killed 164,000 people injured
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Earthquake Precursors Scientists can not predict date and time when earthquake will strike, but do understand which regions are likely to experience earthquakes Objective is to provide reasonably reliable warning of impending earthquake
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Earthquake Precursors Research continues to explore phenomena that warn of imminent earthquake Track fault movement to anticipate when it will break Monitor deformation with GPS (Global Positioning System) Anticipate accumulation of stress necessary to break fault loose at predictable time Stress applied at constant rate does not produce results at constant rate Far more complicated conditions include juxtaposing different rock types with different strengths, changing stress patterns after nearby earthquakes
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Fig. 4-2, p. 71
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Earthquake Precursors Swarms of minor earthquakes or foreshocks may announce onset of fault slippage Swarms precede 1/3-1/2 of earthquakes overall but only small percentage of large earthquakes Difficult to distinguish from background activity Study of microearthquakes identifies previously unknown faults Impossible to determine in advance if a given small earthquake is foreshock or ordinary small earthquake
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Earthquake Precursors Change in levels of radon is possible earthquake precursor Rare gas forms as part of uranium’s decay chain Forms no chemical compounds Remains trapped in rock until escapes along fracture Formation of new fractures before large earthquake may allow radon to escape closer to ground surface (and may cause drop in water table) Changes detectable as increase in radioactivity of groundwater wells
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Earthquake Precursors Change in ground elevation is possible earthquake precursor In 1975, geologists noticed rise in surface elevation near Palmdale, California Accompanied by drop in groundwater level, increase in background radiation
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chapter4 - Click to edit Master Prediction Earthquake title...

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