This morning Oklahoma experienced another small sequence of earthquakes. (There was also a large earthquake with an estimated magnitude of 7.8 in Iran over night.) While I'm preparing for a conference very soon I'm a bit crunched for time, but thought a short post would be in order. I would like to write a few posts concerning what magnitude is, how we calculate it, and other common questions I get asked at some point in the near future.
Okay, here's the synopsis of the most recent events. Early this morning at 01:56:29.875 CDT a magnitude 4.7 earthquake occurred centered northeast of the Oklahoma City metro area. There have been a few significant aftershocks at magnitude 3.0, 3.6, and 4.6. It is notable that there was a higher number of seismic events (though all small) beginning yesterday. All these numbers are from the Oklahoma Geological Survey, the USGS estimates are lower with the largest events at 4.3, 4.2, and 3.3. These magnitudes are computed on slightly different scales, but either way the largest earthquake released over 10 times LESS energy than the earthquakes last year.
The USGS did you feel it program has already collected around 1600 responses and the shaking reported matches very well with what was expected, probably due to the DYFI scale being pretty accurately calibrated after the large earthquake sequence last year. It was striking that the vast majority of the responses came within 90 minutes of the quakes indicating the people actually got up and reported as soon as the event was over. These responses really help the folks at the national earthquake information center (NEIC) and if you felt the earthquake but didn't go fill one out you should!