Friday, August 20, 2010

ASU's Arrowsmith: "big one" is overdue in California

Southern California appears to be overdue for a major earthquake, according to a new study just published by a team including two ASU geology researchers, Ramon Arrowsmith and Olaf Zielke. The article in the September issue of GSA's Geology concludes:
The average time interval between the last six earthquakes that ruptured the San Andreas fault in the Carrizo Plain is 88 ± 41 yr. This is less than the time since the most recent A.D. 1857 earthquake, less than all reported average intervals of prehistoric earthquakes along the entire San Andreas fault, and significantly shorter than the 235 yr average used in recent seismic hazard evaluations. The new chronological data combined with recent slip studies imply that the magnitudes of the earthquakes that ruptured the southern San Andreas fault in the Carrizo Plain since ca. A.D. 1360 were variable, and suggest that the widely held view of rare but great surface rupturing earthquakes along this portion of the southern San Andreas fault should be reevaluated.

The article is getting a lot of attention in California. Ramon has posted a link to the full paper on his blog, along with balloon-borne photos and links to related papers. He says the figure at right is the key one.

Ref: Century-long average time intervals between earthquake ruptures of the San Andreas fault in the Carrizo Plain, California, by Sinan O. Akçiz, Lisa Grant Ludwig, J Ramon Arrowsmith and Olaf Zielke, Geology, doi: 10.1130/G30995.1 v. 38 no. 9 p. 787-790

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