SEPTEMBER MONTHLY HAZARD: EARTHQUAKES

It shakes the walls and floor–maybe even wakes you up. There are many small naturally-occurring earthquakes in Oklahoma, in the past recorded at about one every two years in Tulsa County. Oklahoma is most likely affected by the New Madrid Fault in the Missouri Bootheel, the Meers Fault located in SW Oklahoma near Lawton, and the Nemaha Fault, running north from Oklahoma up through Topeka KS. In recent years, central and north-central Oklahoma has experienced a dramatic increase in seismic activity related to man-made activities. The Oklahoma Geological Survey has determined that the majority of these earthquakes are very likely triggered by the injection of produced water in disposal wells.

The destructiveness of an earthquake depends upon a number of factors, including the magnitude of the tremor, direction of the fault, distance from the epicenter, regional geology, local soils, and the design characteristics of buildings and infrastructure (such as roads, bridges, and pipelines). Un-reinforced masonry structures are the most vulnerable, while wood frame structures typically perform well. Unless secured and braced properly earthquakes can cause mobile homes to topple off their foundations. Earthquakes can cause damages to foundations and ceilings.

There are two ways of rating earthquakes: magnitude (using the Richter scale) measures total energy released; intensity (modified Mercalli) measures the observable effects. A “major” earthquake is at least 4.9 on the Richter Scale–when windows break, objects fall off shelves, and everyone feels it. In 2016, Oklahoma’s strongest recorded earthquake was 5.8 in Pawnee, OK along with two others at 5.0 and above, all associated with pressure on fault lines in the Arbuckle formation from disposal wells’ wastewater injection.

In 2016, the Oklahoma Corporation Commission reduced the rate of injection in the disposals and there has been a related drop in seismicity (earthquake activity).

The US Geological Survey released this map in March 2017 showing Oklahoma has increased in chances for natural and human-induced seismic activity in 2017. Its 2016 predictions were quite accurate for Oklahoma.

Nearly all other continental states have decreased risk of earthquakes in 2017, even those which used to have more injection-well activity.

For more information on earthquakes in Oklahoma, the Office of the Oklahoma Secretary of Energy and Environment has set up a one-stop website source at https://earthquakes.ok.gov/.

For more on what to do before, during or after an earthquake, go to the Federal Alliance for Safe Homes (FLASH).