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Pleasanton Weekly

Opinion - July 5, 2013

Letters

About earthquakes

Dear Editor,

Regarding your May 31 Streetwise question about earthquakes in our area, in earthquake country, quake probability increases with time since the last major earthquake. Tectonic stresses build up over time until released. Faults in the Bay Area represent the boundary between the Pacific Plate and the North American Plate, and these two plates have been grinding together for millions of years and we can expect more periodic earthquakes. Estimates for the average recurrence interval for a major earthquake (7M) on the Hayward Fault range from about 140 to 210 years, and the last major quake on that fault was 1868.

Pleasanton is close enough to the major faults (Hayward, Calaveras, San Andreas Faults) to have very strong ground shaking with potential landslides, liquefaction, etc. Additionally, other lesser active faults in the vicinity are capable of damage (e.g., Greenville Fault).

The following is info from the 2007 WGCEP for its 30-year prediction time frame:

* 15% chance for a 7.5 M or greater in Northern California (the 1989 Loma Prieta quake was 6.9 M)

* 63% chance for a 6.7 M or greater in the Bay Area

* 31% chance for a 6.7 M or greater for the Hawyward-Rodgers Creek Fault (another source uses 19.4% probability for the Southern Hayward Fault)

* 7% for the Calaveras Fault (located west of I-680/Foothill Road

For earthquake info, Google the Pleasanton Seismic Safety Element, ABAG (for earthquake scenarios), USGS, WGCEP, California Geological Survey, FEMA, etc.

The good news is that there is much info available and potential earthquake damage/injury can be reduced with proper preparedness and actions.

George Reid

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