Abstract

Determination of precise depths and moment magnitudes of small‐magnitude earthquakes using regional network stations is important to understand earthquake source processes and seismic hazard. We present a technique that can accurately determine depths and moment magnitudes of small‐magnitude earthquakes using only one or a few regional seismic stations. We filter the observed seismograms as well as synthetic seismograms through a frequency band of 1–3 Hz, which has a good signal‐to‐noise ratio (SNR) for small earthquakes of the magnitude that we are working with. The waveforms are processed to their envelopes to make the waveforms relatively simple for the modeling. We tested the method on 17 aftershocks of modified duration magnitude (MD*) between 3.62 and 2.49 and 1 aftershock of magnitude Mw 3.14 of the 2011 Mw 5.7 Mineral, Virginia, earthquake. We have also tested the method on five aftershocks of local magnitude (ML) between 3.7 and 2.3 of the 2013 Mw 4.5 Ladysmith, Quebec, earthquake. Tests of our method for different crustal models show that event focal depth determinations increase with smaller crustal thickness. The moment magnitudes obtained from our method show variations of 0.16 magnitude units and less for the different crustal structures that we tested. Our study confirms that the envelopes of seismic waveforms can be used to extract accurate focal depths and moment magnitudes of earthquakes as low as Mw 2.6 using only one or a few regional seismic network stations at epicentral distances of 68–424 km.

You do not currently have access to this article.