john's blog

Defining the polygon below:

Earthquake in Chile with tsunami watch and warning.  Areas of the Pacific should take precausions, including Hawaii and Japan, among other areas.  Depth shallow, about 10 km.  Screenshot of earthquake location below, with forecast contours for M>6.5.  The forecast was computed at midnight last night - forecasts are updated every night at midnight California time.

We often get asked this question.  Here is one opinion after the recent March 28, 2014 Brea/La Habra (Los Angeles) California earthquake.

http://video.cnbc.com/gallery/?video=3000262924

March 31, 2014.

http://video.foxnews.com/v/3414210056001/california-earthquakes-a-precur...

The earthquake occurred last night at about 9:09:42 pm PDT. Below are some screenshots and simple analysis of future earthquake risk taken from the Hazard Viewer.

The epicenter was closest to the Puente Hills mapped fault:

(Updated 10:45 PDT 3/17/2014)

A moderate earthquake occurred this morning at 0625 am PDT.  It was centered at a location 9 km NNW of Westwood, CA, where the University of California at Los Angeles is located.  A screenshot from the Open Hazards Hazard Viewer is shown below:

The earthquake occurred at 0700 PDT, 7 hours after the forecast for the figure below was computed (it is computed at midnight).  Using the hazard viewer, we can draw a circle of 100 km radius around the epicenter.  The forecast table (lower left corner) indicates that there was a 25% chance of an M>6 earthquake within the next year, and a 91.6% chance within the next 3 years. 

(Update on March 11:  The magnitude has been further refined to 6.8 rather than 6.9)

There will be the inevitable speculation about whether the earthquake yesterday in South Carolina was related to fluid reinjection.  One way to think about this is to look at the drilling sites in the United States that may have reinjection wells associated with them.  I show such a map below that originates from here.  You can see that the number of wells on the border of South Carolina and Georgia (where the earthquake occurred) is rather low, by comparison with other parts of the country. 

An unusual event in South Carolina just occurred, a magnitude 4.1 event.  At the present time, there is no reason to think this is anything but a relatively rare event.  However, it should also be recalled that Charleston, South Carolina was destroyed by a major earthquake on August 31, 1886.  Estimates place the magnitude in excess of 7, possibly as large as 7.3 moment magnitude.  So while unusual, earthquakes are not unknown in this area. 

Check out the course I am teaching this winter quarter at the University of California, Davis, California.  Weekly commentary is here.  The lectures can be found in power point form here.  The lectures are by and large taken from material in Wikipedia.