Calfornia-Nevada Forecast, November 1, 2011

The last major earthquake in the California-Nevada region was the April 4, 2010 El Mayor-Cucupah (Baja) earthquake.  With a magnitude M=7.2, this event did over USD$100 million in damage to the surrounding region.  Its effects are still being felt in the enhanced number of smaller earthquakes that have occurred since that date.

Here we post the latest forecast for an event having magnitude greater than M6.0 occurring anywhere within the California-Nevada region over the next 12 months from November 1, 2011.  As in previous forecasts, the figure shows the chance of such an earthquake in % as a function of time (year).  The vertical dashed blue lines and the blue dots indicate the M>6 earthquakes that occurred at various times.  As can be seen, the earthquake probabilities decrease sharply just after the earthquake, then recover over time. 

The large events tend to occur when the probability has increased to near 50%.  The large X at the right hand end indicates the probability for such an earthquake today, about 60%.  It can be seen that the current probability is as large as it has ever been.  There appears to be a systematic bias in the computed probabilities from 1985 to the early 1990's, when the data stream became fully automated and digital.  This may be due to systematic undercounting of smaller earthquakes in the earlier time period.  

Technical Backtesting Details:

The figures below show a Reliability diagram and a Receiver Operating Characteristic diagram, two forms of backtesting of the forecasts.  The turquoise areas show the limits on the Briar Score (reliability error) and ROC score for 500 random catalogs constructed in a bootstrap analysis of the error.  These plots indicate that the forecast has reasonable skill and reliability.