Earthquake Swarm Continues in Central Oklahoma plus 1 more

[USGS Newsroom <oc_web@xxxxxxxx>]

Title: USGS Newsroom

Earthquake Swarm Continues in Central Oklahoma plus 1 more

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Earthquake Swarm Continues in Central Oklahoma

Posted: 22 Oct 2013 10:07 AM PDT

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. 

White Sturgeon Hatch-Success Study Yields Clues to Restoration Strategy

Posted: 22 Oct 2013 10:00 AM PDT

COOK, Wash. — The eggs of endangered Kootenai River white sturgeon are less likely to hatch on some of the surfaces that have been made more common by human, or anthropogenic, changes on the river, a new U.S. Geological Survey report has found.

The white sturgeon (Acipenser transmontanus), once common in much of North America, is a very large, slow-to-mature fish that has evolved little from its late Cretaceous ancestors 175 million years ago. It has great cultural significance for the Kootenai Tribe of Idaho and many other Northwest Tribes. White sturgeon was harvested in many places for caviar, and dams and other development have altered its habitat in ways whose implications are still being studied. White sturgeon in Idaho and Montana’s Kootenai River basin were listed as endangered in 1994, and poor recruitment (the number of a species’ young to survive to maturity) in other West Coast populations is a concern.

"Sturgeons are imperiled across the globe. Our scientists are committed to working with partners, including tribes, to address sturgeon issues across the region," said Jill Rolland, director of the USGS Western Fisheries Research Center.

In the report, prepared in cooperation with the Kootenai Tribe of Idaho, USGS research fishery biologist Mike Parsley and biological science technician Eric Kofoot examined hatch success in the laboratory on various surfaces, such as clean rocks, algae-covered rocks and sand, that sturgeon eggs settle and adhere to in the wild while they develop into larvae. The scientists found sand to be a poor surface, because the developing sturgeon embryos failed to attach to it. River rocks covered in algae yielded poor results, in part because they were more hospitable to fungus that threatens sturgeon embryos, while waterlogged wood and clean rocks performed well.

The report notes that sand substrates, or surfaces, now dominate the highly altered Kootenai River in areas currently used by spawning sturgeon, and that dam operation for flood management and hydropower during the spawning season have largely eliminated spring scouring flows that typically would clean rocks of algae and other growth. Finally, the report raises several possibilities, based on the findings, for maximizing white sturgeon recruitment, including substrate-type recommendations for spawning-habitat restoration and the incorporation of scouring flows to clean spawning substrate prior to the spawning season. 

"This is another piece in the puzzle of understanding why some white sturgeon populations in highly altered river systems succeed and others don’t," Parsley said.

The publication, "Hatch Success of White Sturgeon Embryos Incubated on Various Substrates," USGS Report Series 2013-5180, by Michael J. Parsley and Eric Kofoot, is available online.