M=4.2 earthquake strikes beneath Mount Baldy Ski Resort in British Columbia, Canada

Ross Stein and Volkan Sevilgen, Temblor

The earthquake stuck at a relatively shallow depth of 5-7 km (3-4 mi) and was felt over an area about 100 km (60 mi) wide; the closest town is Oliver, 15 km to the west, where it was strongly felt.

One can see from Temblor’s Earthquake Forecast model (based on GEAR) that a M=4.2 shock at this location is not surprising. The map shows that a M~5.5 would have a 1% per year chance of occurring, or a 57% chance in your lifetime. Because smaller quakes are more abundant, a M=4.2 has about a 5% per year chance of occurring.

Temblor web app map of today’s earthquake, together with the GEAR earthquake forecast
Temblor web app map of today’s earthquake, together with the GEAR earthquake forecast
Google Earth image of the epicentral region
Google Earth image of the epicentral region

The magnitude seems to us too high, and the depth too great, to be a controlled explosion related to the ski resort. There is no focal mechanism information yet available for the quake, but we anticipate that it will be a thrust event typical of the Canadian Rockies. Natural Resources Canada assigns it a M=4.0 and a depth of 1.0 km, but we believe it would still be too large to be man made.

Data from the U.S. Geological Survey, Pacific Northwest Seismic Network operated by the University of Washington, and the Natural Resources Canada-Geological Survey of Canada

  • John F McBride

    Ross, the Washington State DNR map of faults indicates a zone of complex faulting on the U.S. side of the border, the zone marking a transition from the Pasayten complex on the west to the Okanogan structure to the east. Having driven through that area a number of times one gains the impression of serious faulting from the topography.

    Is it likely that this event, and several others along that transition over the last year down through the Okanogan valley, result from resolution of accumulated shear and or thrust forces along that margin?