WEST VIRGINIA EARTHQUAKES: CRUSTAL ADJUSTMENTS ALONG THE ROME TROUGH OR SOMETHING ELSE?

Since 1966, there have been 33 instrumentally recorded earthquakes recognized in western West Virginia within or adjacent to the structural feature known as the Rome Trough. This structure is a fault-bounded graben involving basement rocks thought to be related to failed rifting of the North American plate during the Precambrian. Eight earthquakes, with mean hypocentral depths of 10.5 km, were located within the boundaries of the Trough; the remaining 25 quakes, with mean depths of 5.8 km, were located to the east of the Trough. This latter group of quakes is bimodally distributed by depth with 11 earthquakes focused at depths of 4 km or less and 14 at depths greater than 4 km. Interestingly, 7 of the 11 “shallow” earthquakes occurred in Braxton County, WV in a single year (2010). These seismic events are clustered geographically near a saltwater disposal well that injects at a depth of 1.7 km in close proximity to a recently discovered normal fault. We speculate that the “deeper” earthquakes are associated with isolated, recurrent fault movements in response to ancient crustal stresses within and along the margins of the Rome Trough. The “shallow” earthquakes recorded in Braxton County may reflect slip related to injection activity on the newly discovered fault.