Name
An Overview of Recent M4+ Earthquake Sequences in BC and AB and Their Controversies
Description
Routine seismic monitoring by NRCan has reported several earthquake series in NE BC and W AB with magnitudes ≥ 4 since November 2022. Built on top of the NRCan catalogue, the Induced Seismicity Research Project investigates the spatiotemporal distribution of local seismicity and their relationship with hydraulic fracturing and/or wastewater disposal operations. In nearly all cases, we can correlate the epicentral distribution of earthquakes with active injections nearby. We found that most induced earthquakes occurred at depths shallower or comparable to that of injections, with some deeper exceptions closer or even well within the basement. Special attention is given to the earthquake sequence near Peace River, AB, with several significant foreshocks during the week before the Mw5.1 mainshock on Nov 30 (Nov 29, local time). This event is probably one of the biggest seismic events in AB since modern earthquake monitoring began. Different inversion methods consistently show that the mainshock occurred on a NW-SE-striking thrust-faulting plane with a centroid depth of 3-4 km. However, we cannot exclude the possibility of an initial rupture at >6 km. Significant foreshocks and aftershocks (M2.5+) seem to have similar thrust focal mechanisms. This pattern of consistent thrust-faulting is in sharp contrast with the much diverse focal mechanism patter of the Musreau Lake sequence between 2018 and 2021. Preliminary relocation of hypocenters suggests that the Nov 30, 2022, sequence may involve at least two seismogenic structures oriented orthogonal to each other, implying possible complicated interactions between tectonic and induced stress perturbations.