Sunday, September 13, 2009

Venezuela Earthquake

Tectonic Summary

The September 12, 2009 earthquake offshore of Venezuela occurred at a shallow depth as a result of right-lateral strike-slip faulting. The tectonics of this area are dominated by the eastward motion of the Caribbean plate with respect to the South American plate, at a rate of approximately 20mm/yr. Major fault systems in the region include the Boconó fault further to the southwest, and the San Sebastián and El Pilar faults which run from west to east near the earthquake epicenter; these faults accommodate the majority of the motion between the two plates. The location of today’s event indicates it may have occurred on the San Sebastián or El Pilar faults, though further analysis of the earthquake is needed.
The region surrounding the September 12th event is known to be seismically active, and has hosted strong earthquakes in the past; previous damaging earthquakes include an M6.5 quake in July 1967 that caused approximately 240 fatalities, and an M5.4 quake in May 1989 which made more than 2000 people homeless in the Tucacas area.


This is a fascinating area for me. The Caribbean Plate is like a bulge that has burst through the North and South American 'wall'. All around it we have volcanoes, and beautiful tropical islands. At the bottom, this bulge has to grind past South America in a giant strike-slip fault, exactly like the San Andreas. So, Ven. is a copy of California, even with wacky politics! :)

With this geology, I'm surprised that their historical seismicity only shows smaller earthquakes. This is not right! A place like this with 20 mm/yr movement should have huge earthquakes! Maybe they are yet to come...

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