Source Parameters of the 16 July 2010 Mw 3.4 Germantown, Maryland, Earthquake

Abstract

The 16 July 2010 M 3.4 Germantown, Maryland, earthquake was the largest recorded earthquake to occur within 50 km of Washington, D.C. I estimated the source parameters of the Germantown earthquake and its M 2.1 aftershock using the empirical Green’s Function (EGF) method. I found that both earthquakes have small‐radius, high‐stress drops (static and dynamic) and high radiated energy, comparable to the source parameters of other Northeastern America earthquakes obtained using similar EGF methods. These results are consistent with previous observations that intraplate earthquakes have higher stress drops than plate‐boundary earthquakes. Higher stress drops of intraplate earthquakes may result from longer healing times and lower strain rates characteristic of intraplate regions. I estimated the frequency‐independent attenuation factor, Q , for all available source‐station paths, constraining the solution with the previously estimated source parameters, and find attenuation to be low, with constant Q varying from 743 to 3000 (maximum resolvable Q ), and 889 to 3000, for P and S waves, respectively, at hypocentral distances from around 100 to 200 km, and at frequencies between 1 and 40 Hz. The occurrence of high‐stress‐release earthquakes within regions where seismic attenuation is low makes these intraplate earthquakes potentially more damaging than their plate‐boundary counterparts.