Case studies – plate tectonics and associated hazards

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Case studies – plate tectonics and associated hazards

San Francisco earthquake

·         The great San Francisco earthquake of 1906 is regarded by many to be particularly significant

·         The primary effects of the shaking and the secondary effects of the fires that followed left large areas of the city destroyed and at least 700 people dead

·         One long term effect of the earthquake involved the rebuilding and re-planning of the city

·         The 1906 earthquake helped inform scientists about the need to avoid building on soft mud and sand which become particularly unstable during an earthquake

·         Earthquakes affect all who live in California regardless of race, age or wealth

·         In Los Angeles, the 6.6 magnitude Northridge earthquake of January 17th 1994 left an immediate death toll of 57 and thousands injured

·         More than 24 hours after the earthquake, 82000 homes and businesses were still without electricity and 50000 without water

·         Overpasses collapsed as the concrete columns supporting upper road sections failed

·         The busiest road in the USA, the Santa Monica Freeway, and the major route northwards, the Golden State Freeway, were both closed

·         The economic cost of the earthquake approached $30 billion – more than 4 times the cost of the 1989 San Francisco Bay area earthquake

·         Ironically, as the epicentre was in the north of the city, some of the poorest areas of Los Angeles suffered less damage, while affluent Santa Monica and Beverly Hills had hundreds of building declared unsafe

·         The San Andreas Fault Observatory at Depth (SAFOD) is an attempt to finally understand what triggers earthquakes, even to observe the earthquake as it happens several kilometres below the ground

·         SAFOD began in the summer of 2002 when a 2.2km ‘L’ shaped hole was drilled across the San Andreas fault at Parkfield, a rural site situated halfway between Los Angeles and San Francisco

·         Seismometers, thermometers and other sensitive recording equipment have been placed in the cement-filled borehole to monitor future earthquakes

·         Scientists hope that such information may help them to predict earthquakes in the future

An example of a hot spot – Hawaii:

·         In December 2009, scientists were at last able to end a 40 year debate

·         The existence of volcanoes in the middle of plates, such as the Hawaiian Islands and Emperor Seamount chains, had proven to be difficult to fit into the newly-developing plate tectonic theory

·         Now, networks of seismometers on land and the sea floor around Hawaii have provided the first seismic images of this missing jigsaw piece of plate tectonic theory – a mantle plume or hot spot

·         As the less dense magma pushes through the lithosphere, the movement is picked up by the delicate seismometers

·         Following the analysis of 2 years of data from the PLUME (Plume-Lithosphere Undersea Melt Experiment) project, the first images of…

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