Sources of shaking and flooding during the Tohoku-Oki earthquake: A mixture of rupture styles

Modeling strong ground motions from great subduction zone earthquakes is one of the great challenges of computational seismology. To separate the rupture characteristics from complexities caused by 3D sub-surface geology requires an extraordinary data set such as provided by the recent Mw9.0 Tohoku-Oki earthquake. Here we combine deterministic inversion and dynamically guided forward simulation methods to model over one thousand high-rate GPS and strong motion observations from 0 to 0.25 Hz across the entire Honshu Island. Our results display distinct styles of rupture with a deeper generic interplate event (∼Mw8.5) transitioning to a shallow tsunamigenic earthquake (∼Mw9.0) at about 25 km depth in a process driven by a strong dynamic weakening mechanism, possibly thermal pressurization. This source model predicts many important features of the broad set of seismic, geodetic and seafloor observations providing a major advance in our understanding of such great natural hazards.

► The slip model explains wide range of the data including ground motion from 10 s period to static. ► Shaking came from the deeper rupture and the tsunami originated from very large slip at shallow depth. ► Using refined source model with 3D crustal model provides improved fit to observed motions.