Wednesday, March 05, 2014

USGS: Oklahoma Earthquake Swarm Update

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M2.5+  Swarm last 7 Days -  Credit USGS  Earthquake Map

 

# 8351

 

Last November, in Oklahoma Insurance Commissioner Warns On Earthquake Risks,  I wrote about the recent uptick in moderate earthquake activity in and around Oklahoma City, OK which began in earnest back in 2009. This `swarm’ includes the largest earthquake ever reported in Oklahoma, a 5.6 Mag Quake near Prague on Nov. 5, 2011.


While most of Oklahoma’s temblors since then have come in under 4.0, on average they’ve seen at least a couple of 2.5+ quakes every day for the past month.  Not strong enough to cause significant damage, but strong enough to be felt, and to raise concerns.

 

Today, the USGS is reporting a M3.9 - 9km E of Edmond, Oklahoma, the strongest temblor in that region since February 8th’s M4.1 quake. 

 

Earlier this year, the USGS produced the following update, which links the increase in earthquake activity in the Midwest and East to induced seismicity – or man-made causes.

Man-Made Earthquakes Update

Categories: Featured, Natural Hazards
Posted on January 17, 2014 at 1:00 pm
Last update 2:03 pm By: William Ellsworth (ellsworth@usgs.gov), Jessica Robertson (jrobertson@usgs.gov), and Christopher Hook (703-648-4460)

Seismicity of the coterminous United States and surrounding regions, 2009–2012. Black dots denote earthquakes with a magnitude ≥ 3.0 are shown; larger dots denote events with a magnitude ≥ 4.0. Background colors indicate earthquake hazard levels from the U.S. National Seismic Hazard Map (NSHM). Learn more about the NSHM at http://earthquake.usgs.gov/hazards/?source=sitenav.

Seismicity of the coterminous United States and surrounding regions, 2009–2012. Black dots denote earthquakes with a magnitude ≥ 3.0 are shown; larger dots denote events with a magnitude ≥ 4.0. Background colors indicate earthquake hazard levels from the U.S. National Seismic Hazard Map (NSHM). Learn more about the NSHM at http://earthquake.usgs.gov/hazards/?source=sitenav.

 

The number of earthquakes has increased dramatically over the past few years within the central and eastern United States. Nearly 450 earthquakes magnitude 3.0 and larger occurred in the four years from 2010-2013, over 100 per year on average, compared with an average rate of 20 earthquakes per year observed from 1970-2000.

This increase in earthquakes prompts two important questions: Are they natural, or man-made? And what should be done in the future as we address the causes and consequences of these events to reduce associated risks? USGS scientists have been analyzing the changes in the rate of earthquakes as well as the likely causes, and they have some answers.

USGS scientists have found that at some locations the increase in seismicity coincides with the injection of wastewater in deep disposal wells. Much of this wastewater is a byproduct of oil and gas production and is routinely disposed of by injection into wells specifically designed for this purpose.

Review Article on Injection-Induced Earthquakes

U.S. Geological Survey geophysicist William Ellsworth reviewed the issue of injection-induced earthquakes in a July 2013 study published in the journal Science. The article focused on the injection of fluids into deep wells as a common practice for disposal of wastewater, and discusses recent events and key scientific challenges for assessing this hazard and moving forward to reduce associated risks.

What is Induced Seismicity?

Although it may seem like science fiction, man-made earthquakes have been a reality for decades. It has long been understood that earthquakes can be induced by impoundment of water in reservoirs, surface and underground mining, withdrawal of fluids and gas from the subsurface, and injection of fluids into underground formations.

(Continue . . . )

While the scientific debate over the exact cause of, and best remedy for, this increased seismic activity continues, last October the USGS warned (bolding mine):

 

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.

 

Which means that Oklahomans (and anyone else who lives an a seismically active region) need to seriously include earthquake preparedness as part of their overall emergency plans. 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, much of America’s heartland and parts of the Eastern Seaboard are also susceptible to moderate to strong quakes.   A topic I covered more than a year ago in USGS: Eastern Earthquakes - Rare But Powerful

 

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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.

 

FEMA http://www.fema.gov/index.shtm

READY.GOV http://www.ready.gov/

AMERICAN RED CROSS http://www.redcross.org/

For more on increasing your level of preparedness, a partial list of some of my preparedness blogs include:

When 72 Hours Isn’t Enough

In An Emergency, Who Has Your Back?

An Appropriate Level Of Preparedness

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