Wednesday, April 07, 2010

Sierra El Mayor (Baja) quake rupture is 28 km long, with 2.5 m offsets

Reports from yesterday's initial helicopter recon on what has been named the Sierra El Mayor earthquake, found offsets of 2.5 meters along a 28 km-long rupture zone on the Borrego fault in northern Baja.   A summary is posted on the Southern Calif. Seismic Network webpage at

The SCSN report also says "the initial portion of rupture process likely began on Pescadoros fault. There may have been pause, possibly 8-10 secs, at which time the trigger of much larger rupture on the Borrego fault occurred. The total slip on the Pescadoros fault was relatively minor and localized.

"Extensive liquefaction phenomena were observed along canal levees, which also contained top shattering. The northwest end of the fault rupture on the Borrego fault demonstrated fault splays, located on the west side of the El Centinela mountain. Other phenomena were also observed or reported, such as minor flooding, ground failure/cracking (not related to faulting), and sand blows."

The recon team took 1300 photos and say many will be made public shortly.   The investigators are from Centro de Investigación Científica y de Educación Superior de Ensenada, BC. (CICESE), USGS, CalTech, and San Diego State.

Dave Applegate, head of the USGS Earthquake program in Reston VA, gave me the heads up this morning on the SCSN report and also noted that more than 76,000 residents of the region, many from Arizona, have reported what effects they felt or saw from the main shock.   The map of responses is at

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