Avian Flu Diary: USGS: Oklahoma Earthquake Swarm Continues

3.5+Mag quakes – Credit USGS

# 7887

Almost 2 years ago, in November of 2011, I wrote about a 5.6 Mag Quake that Rattled Oklahoma. At the time I noted that the state of Oklahoma had seen an unusual number of earthquakes over the previous couple of years. In 2010, the Oklahoma Geological Survey Observatory recorded 1,047 earthquakes, of which 103 were strong enough to be felt by the public.

Since that time, Oklahoma’s earthquake swarm has continued, producing more than 200 3.0+ magnitude temblors over the past 4 years.

Today the USGS, in partnership with the Oklahoma Geological Survey, has released a report on this ongoing swarm, and how it affects the risks for seeing larger quakes in the region. I’ve excerpted the key message (bolding mine) below:

Important to people living in the Oklahoma City region is that earthquake hazard has increased as a result of the swarm. USGS calculates that ground motion probabilities, which relate to potential damage and are the basis for the seismic provisions of building codes, have increased in Oklahoma City as a result of this swarm. While it’s been known for decades that Oklahoma is "earthquake country," the increased hazard has important implications for residents and businesses in the area.

The full news release follows:

Earthquake Swarm Continues in Central Oklahoma

Released: 10/22/2013 1:07:59 PM

Contact Information:
U.S. Department of the Interior, U.S. Geological Survey
Office of Communications and Publishing
12201 Sunrise Valley Dr, MS 119
Reston, VA 20192
Heidi Koontz
Phone: 303-202-4763

In partnership with: Oklahoma Geological Survey

Since January 2009, more than 200 magnitude 3.0 or greater earthquakes have rattled Central Oklahoma, marking a significant rise in the frequency of these seismic events.

The U.S. Geological Survey and Oklahoma Geological Survey are conducting collaborative research quantifying the changes in earthquake rate in the Oklahoma City region, assessing the implications of this swarm for large-earthquake hazard, and evaluating possible links between these earthquakes and wastewater disposal related to oil and gas production activities in the region.

Studies show one to three magnitude 3.0 earthquakes or larger occurred yearly from 1975 to 2008, while the average grew to around 40 earthquakes per year from 2009 to mid-2013.

"We've statistically analyzed the recent earthquake rate changes and found that they do not seem to be due to typical, random fluctuations in natural seismicity rates," said Bill Leith, USGS seismologist. "These results suggest that significant changes in both the background rate of events and earthquake triggering properties needed to have occurred in order to explain the increases in seismicity. This is in contrast to what is typically observed when modeling natural earthquake swarms."

The analysis suggests that a contributing factor to the increase in earthquakes triggers may be from activities such as wastewater disposal--a phenomenon known as injection-induced seismicity. The OGS has examined the behavior of the seismicity through the state assessing the optimal fault orientations and stresses within the region of increased seismicity, particularly the unique behavior of the Jones swarm just east of Oklahoma City. The USGS and OGS are now focusing on determining whether evidence exists for such triggering, which is widely viewed as being demonstrated in recent years in Arkansas, Ohio and Colorado.

This "swarm" includes the largest earthquake ever recorded in Oklahoma, a magnitude 5.6 that occurred near Prague Nov. 5, 2011. It damaged a number of homes as well as the historic Benedictine Hall at St. Gregory's University, in Shawnee, Okla. Almost 60 years earlier in1952, a comparable magnitude 5.5, struck El Reno and Oklahoma City. More recently, earthquakes of magnitude 4.4 and 4.2 hit east of Oklahoma City on April 16, 2013, causing objects to fall off shelves.

Following the earthquakes that occurred near Prague in 2011, the agencies issued a joint statement, focusing on the Prague event and ongoing seismic monitoring in the region. Since then, the USGS and OGS have continued monitoring and reporting earthquakes, and have also made progress evaluating the significance of the swarm.

Important to people living in the Oklahoma City region is that earthquake hazard has increased as a result of the swarm. USGS calculates that ground motion probabilities, which relate to potential damage and are the basis for the seismic provisions of building codes, have increased in Oklahoma City as a result of this swarm. While it’s been known for decades that Oklahoma is "earthquake country," the increased hazard has important implications for residents and businesses in the area.

To more accurately determine the locations and magnitudes of earthquakes in Oklahoma, the OGS operates a 15-station seismic network. Data from this system, and from portable seismic stations installed in the Oklahoma City region, are sent in real-time to the USGS National Earthquake Information Center, which provides 24x7 reporting on earthquakes worldwide.

The State of Oklahoma maintains an earthquake safety webpage at EARTHQUAKE SAFETY, while additional Oklahoma specific earthquake monitoring and research information can be found at the Oklahoma Geological Survey.

Although the west coast is most noted for its seismic hazards, America’s heartland and parts of the Eastern Seaboard are susceptible to moderate to strong quakes. A topic I covered about a year ago in USGS: Eastern Earthquakes - Rare But Powerful

Given the risks, the United States government devoted their National Level Exercise (NLE 2011) two years ago to a simulated catastrophic earthquake in the New Madrid Seismic Zone (NMSZ).We live on a violent planet, one that is prone to storms, fires, floods, drought, volcanoes, earthquakes and myriad other natural disasters.Emergencies happen every day.

Disasters, admittedly, less often. But in either event, preparedness is key.

At a bare minimum, every household should have a disaster plan, a good first aid kit (and the knowledge to use it), an emergency battery operated NWS weather radio, and emergency supplies to last a minimum of 72 hours during a disaster.To become better prepared as an individual, family, business owner, or community, I would invite you to visit the following preparedness sites.