Los Angeles Earthquakes

john's picture

On June 2 a news item in the LA Times described a recent increase in the number of magnitude > 4 earthquakes in the Los Angeles area.  I thought I would take a look at the situation using the hazard viewer on this site.  We can start by defining the circular selection region.

Using the View Strain tool, we can examine the cumulative strain release in the circular area since 2004.

Putting a ruler against the red line, it does not appear that there has been any significant change in the energy release since 2004.  The mix of earthquakes may have changed, with more magnitude 4's but the energy release of all the events taken together has been at a relatively constant rate in time. This suggests that the activity is moving from more frequent smaller events towards somewhat larger, less frequent events.

We can also use the hazard viewer to forecast future activity in the area.  The table below summarizes the chance of an earthquake for various magnitude ranges and future time intervals.

We can also compute the chance of an earthquake to see how it changes in time.  The chance of another M>5 event, at 58.3% for the next year, is significant.  The probability of 99.9% over 3 years says that it would be very surprising not to see such an event within the next 3 years. The chance of an M>6 event within 1 year is low, about 5.5%, but rises to 39% within 3 years, which is again significant.

Below is a chart for M>5: