Detecting previously unknown aftershocks of the 2011 Tohoku quake

Abstract

Aftershocks of major earthquakes are usually detected by local seismic monitors, but they can also be detected by more distant seismic arrays. Kiser and Ishii used a technique known as back projection to analyze data from North American seismic stations during the 25 hours following the 2011 magnitude 9 Tohoku earthquake. They compared their data with the aftershock catalog from the Japan Meteorological Agency (JMA), which is based on data from local seismic arrays, and found that about half of the aftershocks they detected within the North American data were not included in the JMA catalog. Most of these events took place near the Japan Trench in an area previously thought to be relatively aseismic following the magnitude 9 mainshock. The new data help fill in the record of aftershock distribution for the Tohoku earthquake and demonstrate the usefulness of back‐projection analysis of teleseismic data in detecting aftershocks of major earthquakes.