Why We Have Earthquakes in the Eastern United StatesJ. K. Costain
Virginia Tech, Blacksburg, VA, USA
There are only two types of naturally-occurring earthquakes anywhere on the Earth: 1) those associated with the dynamics of plate tectonics and 2) those associated with the dynamics of the hydrologic cycle. The first type is characteristic of an INTERplate setting (like the San Andreas Fault). The second (“hydroseismicity”) is characteristic of an INTRAplate setting (like the Virginia magnitude 5.7 earthquake of August 23, 2011. The second type is caused by the dynamics of groundwater recharge, hurricanes, and typhoons, which trigger the intraplate earthquakes. COMSOL Multiphysics® Finite element models (FEMs) are useful as a way to examine the buildup of pore-fluid pressure in fracture zones. The earthquakes typically follow weather disturbances in pore-fluid pressure by 60-90 days.