|MadSci Network: Earth Sciences|
Mark, Interesting question. Heat from global warming would have to penetrate several kilometers into the Earth to affect the earthquake frequency. Rock is actually a fairly good insulator so it would take hundreds to thousands of years for heat to penetrate deep enough to reach the focal depth of earthquakes. Earthquakes occur as deep as 800 km, but most are much closer to the surface. The sources of volcanoes are also fairly deep, on the order of 20 to 60 km. A change in the surface temperature would take thousands of years to penetrate that far. A question that comes up fairly often is is the frequency of earthquakes increasing. The answer is no. What has increased is the ability to record and locate smaller earthquakes. Earthquakes of magnitude of 6.5 and above have generally been well located anywhere in the world since at least 1900. The number of these earthquakes has been fairly steady at roughly 152 per year on average. In 1963 the World Wide Seismic Standard Seismograph Network came on line. The number of well located earthquakes of magnitude 4.5 and above jumped. This was not an increase in the frequency of earthquakes, it was an increase in the ability to detect them. Also reports of distant disasters have been covered more in the news media. David A couple of web sites that may be of interest are: National Earthquake Information Center A paper by V. G. Kossobokov
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