Thursday, March 23, 2007

Deep-diving West Coast Plate May Have Triggered Massive Central U.S. Quake

Seismic News: USA

Deep-diving West Coast Plate may have triggered the massive Central U.S. quake - Scientists studying extraordinary earthquakes in the central U.S. in 1811-12 along the New Madrid seismic zone have revealed a possible new driving mechanism. Remnants of the ancient Farallon plate, a slab of crust swallowed beneath the western North American continental margin nearly 70 million years ago, continue to descend into the deep mantle under central North America. The descent induces mantle flow towards the Earth''s deep interior directly below the New Madrid seismic zone. That flow, in turn, may strain the overlying crust, causing seismic ruptures.

National Geographic April 2007

Giant earthquakes hit this zone about every 500 years; geologist estimate a 10 percent chance of an event equal to the 19th-century within 50 years. - Chris Carroll

Thursday, March 15, 2007

Did quake signal more to come?

Breaking Seismic News: Ohio, USA

Monday's 3.6 earthquake in Portage County was the latest in Northeast Ohio. The epicenter was along the Akron Magnetic Lineament, the broad fault zone on which a 5.0-magnitude earthquake in southern Lake County occurred in 1986. That earthquake shattered glass and prompted the federal government to raise Ohio's earthquake risk from low to moderate. Earthquakes in this region, though mostly minor, are becoming more common. "This could be a fore-shock to a bigger one, but that's pretty unlikely." Fourteen earthquakes shook Northeast Ohio last year. The most severe was in June near Painesville and had a magnitude of 3.8. Many of the earthquakes occurred beneath Lake Erie, where there may be unconfirmed fault lines. "California's rocks are much younger. They're hotter rocks, and they're more structurally complex. They're twisted and folded around a lot. An earthquake in California occurs, and it causes damage in a certain area. But if we have that same size earthquake here in the East, it does damage in about a 10-times greater area because our rocks are flat-lying rocks. They're old, cold, brittle, and energy goes [through them] for a long distance."

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