Seismic b value within the Montney play of northeastern British Columbia, Canada

Abstract

Critical analysis of induced earthquake occurrences requires comprehensive data sets obtained by dense seismographic networks. In this study, using such data sets, I take a detailed investigation into induced seismicity that occurred in the Montney play of northeastern British Columbia, mostly caused by hydraulic fracturing. The frequency–magnitude distribution (FMD) of earthquakes in several temporal and spatial clusters show fundamental discrepancies between seismicity in the southern Montney play (2014–2018) and the northern area (2014–2016). In both regions, FMDs follow the linear Gutenberg–Richter (G–R) relationship for magnitudes up to 3.0. While in southern Montney, within the Fort St. John graben complex, the number of earthquakes at larger magnitudes falls off rapidly below the G–R line, within the northern area with a dominant compressional regime, the number of events increases above the G–R line. This systematic difference may have important implications with regard to seismic hazard assessments from induced seismicity in the two regions, although caution in the interpretation is warranted due to local variabilities. While for most clusters within the southern Montney area, the linear or truncated G–R relationship provide reliable seismicity rates for events below magnitude 4.0, the G–R relationship underestimates the seismicity rate for magnitudes above 3.0 in northern Montney. Using a well-located data set of earthquakes in southern Montney, one can observe generally that (1) seismic productivity correlates well with the injected volume during hydraulic fracturing and (2) there is a clear depth dependence for the G–R b value; clusters with deeper median depths show lower b values than those with shallower depths.