The 17 May 2013 M 4.6 Ladysmith, Quebec, Earthquake

Abstract

Although moderate in size ( M N 5.2, M 4.6), the earthquake that occurred near Ladysmith, Quebec, on 17 May 2013 was one of the best‐recorded earthquakes to have occurred in eastern Canada in recent years due to the fortuitous deployment of U.S. Transportable Array stations in a region that was already well covered by the Canadian National Seismograph Network. This data set allowed us to study the earthquake and its aftershocks in better detail than we could have done in the past. Moment tensor and first‐motion focal mechanisms suggest that it was a typical western Quebec earthquake resulting from thrust faulting on a northwest‐striking plane. Several methods were used to determine the depth, all indicating a depth of 12–15 km. The aftershock sequence, which included a magnitude 4.1 ( M N) earthquake occurring 10 min after the mainshock, was relatively rich in M N>3.0 events and contrasts sharply with that of the 2010 Val‐des‐Bois earthquake (also in western Quebec). Strong‐motion data from the Ladysmith earthquake contributed to an ongoing study to model soft soil amplification and basin effects. The earthquake was felt to distances in excess of 500 km, and more than 4300 people filled out an online “Did You Feel It?” survey, providing a detailed picture of macroseismic effects. Visits to Ladysmith and nearby communities found evidence for minor damage confined to the epicentral area. It is difficult to correlate the Ladysmith sequence with any known faults in the region, but it is noted that some local‐scale lineaments in the epicentral area trend subparallel to the nodal planes of the focal mechanism.