Propagation of Slow Slip Leading Up to the 2011 M w 9.0 Tohoku-Oki Earthquake

Abstract

Before Tohoku-Oki Recordings by Japan's dense seismic network in the days and weeks before the 2011 M w 9.0 Tohoku-Oki earthquake provide an opportunity to interrogate what caused the dynamic rupture of one of the largest earthquakes on record. Using a method to extract small earthquakes that are often obscured by overlapping seismic waves, Kato et al. (p. 705 , published online 19 January) identified over a thousand small repeating earthquakes that migrated slowly toward the hypocenter of the main rupture. Based on the properties of these foreshocks, the plate interface experienced two sequences of slow slip, the second of which probably contributed a substantial amount of stress and may have initiated the nucleation of the main shock.