M5.6 earthquake in Oklahoma

A series of earthquakes has hit Oklahoma, with a M5.6 being the strongest one. The main quake was preceeded by a M4.8 and several smaller ones. A number of aftershocks took place, some of them stronger than M3.0. The epicentre was situated close to Prague about 50 km west of Oklahoma City. All quakes occured in very shallow depth (< 10 km). No injuries have been reported so far, but it seems that some minor damage occured. Quakes of this strength can be felt over hundreds of kilometers in central and eastern US.

This was largest earthquake ever recorded in the state’s history. The Oklahoma Geological Survey provided an earthquake list:

List of largest EQs in Oklahoma without the recent ones (Source: Oklahoma Geological Survey)

The following map illustrates the distribution of the recent events (USGS data via GoogleEarth):

Epicentres of the Oklahoma events (data from USGS, map from GoogleEarth)

The Geological Survey has set up a website with information and published a preliminary report. Instrumental intensities reached V, peak ground acceleration has been reported to be up to 0.5 g:

There are already dozens (hundreds?) of blog posts and YouTube videos discussing the cause of the earthquake series. Most of them relate the event to

  • a sign of God,
  • an alignment of the planets,
  • an increase in sun activity, or
  • the beginning of the apocalypse.

Apart from this funny non-sense, Geology in Motion points out that the quakes occured at the Wilzetta fault, which is situated in the oil-bearing Seminole Uplift structure. The strike-slip mechanism would perfectly fit with that:

Moment tensor solution (Data: USGS)

Ontario Geofish speculates the event could be related to injection measures. The figure presented here illustrating the increase of earthquakes in Oklahoma could be another hint for that.

Who was it?

Christoph Grützner
works at the Neotectonics and Natural Hazards Group, RWTH Aachen University, Germany. He likes the Mediterranean and uses geophysics to search for ancient earthquakes.