If the tragic hurricanes weren’t enough, now Mexico has been struck by a 8.2 earthquake last night.  I covered earthquakes in San Diego last month, but here is another story on the risk of the Big One hitting Southern California – and San Diego is still looking good, relatively:


The U.S. Geological Survey 2014 earthquake forecast indicates that the likelihood of a moderate earthquake – between magnitude 6.5 and 7.5 – has decreased, but the chance of a higher-magnitude quake in the region has increased.

Plate movement
The rate of plate movement along the San Andreas fault is approximately 1.3 inches each year – about the same rate your fingernails grow. A USGS report released March 2 detailed a study of the southern San Andreas fault. The study found evidence of 10 ground-rupturing earthquakes between magnitude 7.0 and 7.5 between 800 A.D. and 1857.

Predictions based on the survey forecast a 16 percent chance of a magnitude 7.5 or larger earthquake near Kern County in the next 30 years.

Prediction models
The USGS cautions that although its most recent prediction model is vastly improved since the version in 2008, it is still an approximation. The USGS uses two kinds of scientific models to predict earthquake probability.
1. The earthquake rupture forecast shows where and when the earth might slip along the state’s many faults.
2. The ground motion prediction model estimates the subsequent shaking given by one of the fault ruptures.

The color-coded data are the state’s forecast from 2014:

(SD in bottom right corner)

The USGS estimates long-term quake hazards to give communities an assessment of risk in their area. More than two-thirds of the nation’s annualized earthquake losses in property and structures will be in California, and in California, 80 percent of the losses will be in these 10 counties:

Top 10 counties by estimated annualized earthquake loss (percent of state total)

1. Los Angeles (30.6%)
2. Santa Clara (8.9%)
3. Alameda (8%)
4. Orange (7%)
5. San Bernardino (6%)
6. Riverside (5.6%)
7. Contra Costa (4.6%)
8. San Francisco (3.8%)
9. San Mateo (3.5%)
10. San Diego (3.3%)

A major earthquake hitting Southern California would be devastating to the region, and is one of the biggest threats to disrupting the housing market.  But hopefully the impact on San Diego housing would be less.

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