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Tuesday
May062014

Update on Oklahoma

The dramatic increase in the number of small earthquakes in Oklahoma during the last few years has been getting much attention from scientists and the media. The USGS and the Oklahoma Geological Survey issued a joint statement yesterday on the possibility of future damaging earthquakes.

Here are some updated plots showing the numbers (updating a previous post on 30 March). The increase in the number of events with magnitudes greater than 3.0 is quite impressive.

 

A common way to analyze the distribution of earthquakes by magnitude in seismology and earthquake science is a Gutenberg-Richter plot, where you plot the common logarithm of the number of earthquakes with a magnitude greater than a particular value versus the magnitude.  A plot of the events from the last 3 and a half years is shown below. The slope of the middle part of the gray line is -1.2 (we refere to the negative of the slope as the b-value).

 

The three markers for earthquakes with magnitudes 5.0 and above are one event, an Mw 5.6 earthquake that occurred near Prague, OK in 2011. Typical b-values are near unity, so this pattern is not too unusual, but the increase in the number of earthquakes shown above is extremely unusual.

The recent activity is believed to be related to fluid injection into the subsurface, which is known to trigger small-to-moderate size earthquakes (USGS page on induced earthquakes). You can follow the Oklahoma geological Survey (@OKearthquakes) and the USGS (@usgs) on twitter for updates.