When it comes to earthquakes and being aware / ready for major earthquakes, you might think of the San Andreas Fault, or places like Japan, Chile, China, Mexico or Indonesia.
However in the past year, there have been two extremely significant earthquakes in the United States that were “outliers” from previous events. Both of these were felt over large areas and measured above 5.5 on the Richter Scale.
- August 23, 2011 – Mineral, VA M5.8 Earthquake
- November 5, 2011 – Sparks, OK M5.6 Earthquake
However, I just recently discovered an incredible post by the US Geological Service (USGS) on the Oklahoma Earthquake. In this post at http://www.usgs.gov/blogs/features/usgs_top_story/oklahoma-struck-by-series-of-quakes/, the following image paints a very clear picture:
This map contains several data sources:
- Historical Earthquakes
- Seismic Hazard Maps (2% in 50 Year ~2500yr Return Period Event)
Combined, these resources show where earthquakes have occurred in Central Oklahoma over the past 30-40 years. As raised in the USGS post:
“Earthquakes are not unusual in Oklahoma; they are often simply too small to be felt. However, earthquake activity in this area has increased over the past 4 years.
From 1972 through 2007, the USGS recorded about two to six earthquakes a year in Oklahoma. But in 2008, earthquake activity began to increase, with more than a dozen earthquakes recorded that year. In 2009, the rate continued to climb, with nearly 50 quakes recorded — many big enough to be felt. In 2010, the trend continued.
There has also been a change in the distribution of the earthquakes.
From 1973 to 2007, the earthquakes were scattered broadly across the east-central part of the State. The events since 2008, however, have been more clustered in the vicinity northeast and east of Oklahoma City and generally southwest of Tulsa. This sequence of earthquakes was in this area.”
Now, take a look at the second image (2008 image) and compare how the earthquake patterns show the void of activity in the Lincoln, Creek, Payne County areas just northeast of Oklahoma City. Looking back, this is quite a remarkable change in the historical pattern. We didn’t have all the pieces to “expect” a M5.6 earthquake in Central Oklahoma, however we did have historical context to significant earthquakes. The previous record for the state was a M5.5 earthquake in 1952 in El Reno, Oklahoma. It had been nearly 60 years since that event (more than 1/2 the age of the state), however the impacts of that event and the lessons learned are important to help people prepare.
The important lesson here is to be prepared and know your historical risk. Earthquakes in Central Oklahoma are no surprise. Their magnitude may be from time to time, but this again is a great example of being prepared for that once in a generation or two event, and how preparedness for that event will pay off. Furthermore, all-hazards preparedness is a major key. Much of Central Oklahoma is prepared for tornadoes, and their preparedness for another hazard may have been the key to quick action during this earthquake.
You never know exactly when a big event like an earthquake will occur, however we can pay attention to the trends and when the out of the ordinary event occurs, we can take the appropriate action required.