FINITE-ELEMENT SIMULATION OF AN INTRAPLATE EARTHQUAKE SETTING - IMPLICATIONS FOR THE VIRGINIA EARTHQUAKE OF AUGUST 23, 2011

One scenario for the tectonic setting of the August 23, 2011 magnitude 5.8 intraplate earthquake in the central Virginia seismic zone (CVSZ) is that the event occurred at the intersection of three fracture zones. In general, three planes intersect at a single point. Seismic reflection data in central Virginia are consistent with two such fracture zones ("planes"') being associated with a Mesozoic extensional fabric, and the third with a gently eastward-dipping Alleghanian transpressional fabric, which is known to have had a strong influence on the localization of later Mesozoic structures. This study examines a finite element model (FEM) of pore-fluid pressure diffusion for which the diffusion is restricted to three such intersecting and hydraulically transmissive fracture zones, with the objective of examining the transient behavior of fluid pressure at the intersection at a depth of 8~km where the earthquake is presumed to have occurred. For the FEM, each fracture zone is recharged at the surface of the Earth by some meteoric disturbance, with subsequent pore-fluid pressure diffusion propagating within each zone to the common intersection.

Differences are compared between 1) times of maxima in baseflow as determined for stream gaging station 02.0350.00 on the James River in the CVSZ and the time of occurrence of the Virginia earthquake, and between 2) theoretical times of maxima in pore-fluid pressure diffusion from an impulsive surface source as computed from the FEM simulation. All results are consistent with the assumptions of ``hydroseismicity'', which attributes intraplate seismicity to the dynamics of the hydrologic cycle.