Aftershock Sequences

Large earthquakes typically produce local stress changes that excite aftershock sequences.  Though smaller in magnitude than the mainshocks that trigger them, the largest aftershocks can produce strong ground shaking and act as tsunami sources.  My work in this area focuses on the detection and characterization of early aftershocks that occur within hours of the mainshock rupture.  Below are results from the early aftershock sequence of the March 11, 2011 Mw 9.0 Japan earthquake.











Figure 1: (Left) Amplitude of high-frequency energy release following the March 11, 2011 Japan earthquake.  Vertical lines show the times of earthquakes reported in the JMA catalogue with the colors indicating the magnitude of the event (yellow: M5.0-5.4, green: M5.5-5.9, red: M≥ 6.0).  The red dots show additional earthquakes reported in the NEIC catalogue.  In addition to the reported events, peaks are observed in the time series that are interpreted as previously undetected aftershocks.  (Right) Results from the first 25 hours of the aftershock sequence show that around 300 small-to-moderate sized earthquakes went undetected during this time by local networks.  Black dots show the locations of events reported in the local JMA earthquake catalogue and red dots are the locations of events detected using Transportable Array data that are not reported in this catalogue.  These undetected events cluster near the Japan Trench.