Four Cities Forecast: California Update (August 31, 2011)

john's picture

Readers of these blogs have seen a series of four cities earthquake forecasts for California, Japan, Greece, Italy and Iran among other countries.  This updated forecast represent the chance of an earthquake during the next 12 months within 150 miles of four California cities, for magnitudes 7.0 and larger. 

Following the El Major-Cucupah (Baja) earthquake of April 4, 2010, there were a large number of small magnitude events.  This method uses these earthquakes as markers to measure the stress buildup prior to the next large earthquake.  According to well-known seismological laws such as the Gutenberg-Richter law, there are, for example, approximately 1000 magnitude 3.0 events for every 1 magnitude 6.0 event.  For that reason, the smaller magnitude events can be used, together with statistical hazard models, to calculate the probability of the next magnitude 6 event, given the number of 3.0 events that have occurred since then.

Following is a plot of the chance of a M>7.0 earthquake for the four California cities of San Francisco, Sacramento, Los Angeles, and San Diego.  In addition, we show at the bottom a plot of the chance of a M>6 earthquake anywhere in the California-Nevada region, assuming that the earthquakes in the region are fully correlated.  

The four cities forecast is shown below.


The table below presents the probabilities in tabular form.

Finally, we show below a forecast for the entire California-Nevada region for M>6 earthquakes during the next 12 months.  The probability computed today is as high as it has ever been for the next 12 months.


KyserM's picture

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