Source Characterization for Two Small Earthquakes in Dartmouth, Nova Scotia, Canada: Pushing the Limit of Single Station

Abstract

Abstract A pair of small earthquakes (MN 2.4 and 2.6, Earthquakes Canada) hit the city of Dartmouth, Nova Scotia, Canada, in early March 2020. The events were recorded by three seismic stations within 200 km, but only one station (HAL, <10  km) is close enough to offer high-quality broadband signals. In this study, we explore their source parameters using the nearest station through waveform modeling. A nearby quarry blast (MN 2.0) with known Global Positioning System coordinates is adopted as a reference for regional velocity model building and location calibration. We first build a half-space velocity model by estimating the P-S travel-time difference of the blast and determine the near-surface velocity through full-waveform modeling (i.e., comparing a set of synthetic waveforms with the observed blast). The velocity model is then used to evaluate the pair of earthquakes, in which waveform fitting and Rg/S amplitude ratios suggest source depths of ∼0.7  km. The epicenters of these two earthquakes are situated in a recently constructed commercial development. Lastly, single-station template matching finds no similar earthquakes near the hypocenters of the two events in the past decade and only three aftershocks in the following four months. Taking advantage of a ground-truth blast and waveform modeling, our study demonstrates the potential to construct a detailed regional velocity model and determine accurate earthquake source parameters in regions where only a single station is available.