Magnitude of the 23 January 2018 M7.9 Alaska Earthquake Estimated from Local Dense Seismic Records in Alaska

Abstract

We apply a novel method to estimate the magnitude of the 23 January 2018 M7.9 Alaska earth-quake using seismic stations recorded at local to regional distances in Alaska, US. We determine the source duration from back-projection results derived from the Alaska stations in a relatively compact azimuth range. Then we calculate the maximum P-wave displacements recorded on a wide azimuth range at distances of 8 to 15 degrees. Combining the source duration and the maximum P-wave displacements, we obtain magnitudes of 7.86–8.03 for the 23 January 2018 earthquake in 3–5 min, very close to the Mw 7.9 determined by the USGS and GCMT. This example validates the new approach for determining magnitude of large earthquakes using local to regional stations, and its time efficiency that magnitudes of large earthquakes can be accurately estimated within in 3–5 min after origin time. Therefore, further application of this new method would help accurate estimation of size of earthquakes that occur off shore and might cause tsunami hazards.