Thursday, October 11, 2012

Earthquake experts see the 'Big One' getting bigger

Recent reports suggest that the major rupture predicted for the southern San Andreas fault could be longer and stronger than the last big quake, shaking from Monterey County down to the Salton Sea.



The "Big One" that has been forecast for the San Andreas fault could end up being bigger than earthquake experts previously thought.

Recent research showing that a section of the fault is long overdue for a major earthquake has some scientists saying the southern portion of the fault is capable of a magnitude 8.1 earthquake that could run 340 miles from Monterey County to the Salton Sea.

That's significantly stronger and longer than the southern San Andreas' last major rupture, in 1857. Such a temblor would cause much more damage because with a larger stretch of the fault rupturing, a larger area would be exposed to the quake and the shaking would last longer.

Whether such a quake would happen in our lifetime had been a subject of hot debate among scientists. That's because until recently, experts believed that a part of the southern San Andreas that runs through the Carrizo Plain 100 miles northwest of Los Angeles would remain dormant for at least another century.

But that rosy hypothesis seemed to be shattered by an August report in the journal Geology by researchers at UC Irvine and Arizona State University, which said that even that section is far overdue for a major quake.

"The next earthquake could be sooner than later," Lisa Grant Ludwig, a study coauthor and UC Irvine earthquake expert, said in August.

According to U.S. Geological Survey seismologist Lucy Jones, who was not involved in the study, it is possible that all 340 miles of the southern San Andreas could rupture.

Such a scenario would trigger a magnitude 8.1 earthquake, said Thomas Jordan, director of the Southern California Earthquake Center, a calculation with which Jones agreed.

"My concern is that we will get a series of large earthquakes along the San Andreas fault," said Jordan, who also was not involved in the study.

Jones refers to such a megaquake as a "wall-to-wall" temblor.

[...]

A magnitude 8.1 wall-to-wall quake would release twice the energy of the 1857 temblor, Jordan said.

The San Andreas has long been considered one of the most dangerous faults in Southern California, in part because of its length. Not only do longer faults produce bigger quakes, but they also emit a type of shaking energy that can travel longer distances ... ► Read the full story by Rong-Gong Lin II in Los Angeles Times



Source: Los Angeles Times / October 10, 2012
Author: Rong-Gong Lin II, Los Angeles Times
Photo: Aerial view of the San Andreas Fault in California / Image Source: Wikipedia. Photographer: Ian Kluft. This image is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.



1 comment:

  1. I can't find any real support for the theory that a particular fault can be "overdue" for an earthquake. We know that certain areas have had large earthquakes in the past, so we know that the potential exists. Geologists estimate the risk based on how many have occurred over a length of time in the past, but the interval between events is not constant. In technical terms, statistical frequency does not imply periodic behavior. Scientists have done a poor job in communicating that; even when they do express the probability correctly, reporters will twist it around to create the "Big One Overdue" headline. In this case, it sounds like the geologists are finding evidence that the probability of a large event is higher than they previously estimated, but I don't think they've found a timer.

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