Earthquake Stress Drop in the Charlevoix Seismic Zone, Eastern Canada.

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. Plain Language Summary: Earthquake source parameter studies provide information related to earthquake processes. The scaling of earthquake source parameters such as stress drop versus seismic moment is important for understanding how the fault rupture process varies with event size. For intraplate seismic zones in eastern North America, such a scaling relationship is less well constrained compared to earthquakes along major plate boundaries (interplate). In this study we use newly available seismic data from a densified local array in Charlevoix, eastern Canada, and a spectral ratio method that minimizes nonsource effects to best constrain the stress drop values for earthquakes within the magnitude range ~2–3.8 to be ~2–200 MPa. Our results thus extend the constant stress drop scaling for eastern North America earthquakes from previous studies to a lower magnitude range. We find that stress drop values are higher within the meteorite impact structure than those outside, highlighting influence from local geology. Key Points: We observe high stress drops (2‐200 MPa) for earthquakes in an intraplate seismic zone near Charlevoix, eastern CanadaCombining our results with results from previous studies, we confirm constant stress drop scaling for earthquakes in eastern North America over M ~2‐5Events within the Charlevoix impact structure have higher stress drops than those outside, suggesting a fault maturity contrast [ABSTRACT FROM AUTHOR]