Earthquake Stress Drop in the Charlevoix Seismic Zone, Eastern Canada

Abstract

Stress drop scaling relations of earthquakes in intraplate seismic zones are less well constrained, partly due to less dense instrumentation and lower seismicity rate. Here we use new data to estimate the static stress drop values of earthquakes in the Charlevoix Seismic Zone in eastern Canada (MN < 4.5), June 2012 to July 2017. We first perform double-difference relocation to obtain the hypocentral distribution of 518 events, which highlights a diffuse distribution within the Charlevoix Seismic Zone, probably related to the highly fractured crust by a Devonian meteorite impact. Using spectral ratios, we obtain stress drop values of 47 events ranging from ~2 to 200 MPa, typical of intraplate earthquakes, and observe an invariant stress drop scaling in the magnitude range Mw 2.2–3.8. Events within the impact structure have higher stress drops than those outside, which may indicate differences of fault maturity of the St. Lawrence paleorift system and the presence of a distributed fracture network.