Earthquake!

Magnitude 4.3 OKLAHOMA
Wednesday, October 13, 2010 at 14:06:29 UTC

At 9:06 AM CDT this morning, I experienced my first earthquake. Yes, here in central Oklahoma! At first I thought something huge had hit our roof, and it felt like the house moved sideways. My second thought was that it was an earthquake, because it felt different than anything I had ever felt. I immediately sent this message to my husband "Wow I think I might have just felt an earthquake or blast of some kind--it shook the house!!! I accessed the USGS (US Geological Survey), but there was no information there or on local news for about 20 minutes.

The earthquake was either 4.3, according to the USGS, or 5.1, according to the Oklahoma GS.



If you visit the website of the Oklahoma Geological Survey and click on "Earthquakes", you are directed to the Leonard Geophysical Observatory, which is located near my hometown. According to the Preliminary Earthquake Report on that website,

This earthquake was located 5 miles ENE of Noble, OK and 8 miles SE of Norman, OK at latitude 35.164 N and longitude 97.316 W. The best estimate of the earthquakes depth is 13 km (8 miles). Felt reports have ranged from Dallas, TX to Wichita, KS and as far east as Arkansas. No aftershocks have been observed as of 5 PM on Oct. 13, but aftershocks are quite likely and some may be felt by local residents. This earthquake did not occur on a known fault, but there are more faults in the rocks in the subsurface of Oklahoma than we could possibly count.

The USGS reported a moment magnitude (Mw) 4.3 and the Oklahoma Geological Survey reported a magnitude (mbLg) of 5.1. So which one is right? They both are, these are two different estimates of an earthquake’s size. They are two common seismological methods for determining the size, or magnitude, of an earthquake, which cannot be measured directly. They often have discrepancies similar to those that we are seeing for this earthquake. It is entirely possible that the magnitude estimates will change over time as further work is done to measure the size of the earthquake. Whether it is a magnitude 4.3, magnitude 5.1, or something in between, it is still a small to moderate sized earthquake. This also makes this earthquake the second or third largest instrumentally recorded earthquake in Oklahoma. Earthquakes of this size have the potential of occurring almost anywhere in Oklahoma at any time.

How ironic that in spite of several trips to California in my lifetime, my first earthquake experience was in Oklahoma.