Total Megathrust Rupture of the 2011 Tohoku-Oki Earthquake evidenced by its Energy release rate

While the vast majority of subduction interface earthquakes remain deeper than approximately 20 km depth, a few rare events rupture the more shallow and seismically slow region near the trench. When such events occur, they have the potential for tremendous tsunami excitation. To date, two such classes are known: 1) slow "tsunami earthquakes", which rupture almost in entirety in this region; and 2) some giant earthquakes that rupture from the base of the seismogenic zone through to the trench - we term these events as 'total megathrust rupture'. In order to evaluate whether an event is a 'total megathrust rupture' we examine the seismically observable relative energy growth, as this method is easily applied to real-time warning. We examine the radiated seismic energy and the cumulative energy release rate of the recent Tohoku-Oki 2011 earthquake as well as other recent large and shallow dip-slip earthquakes, like the Chile 2010, and Sumatra 2004 and 2005 earthquakes. After comparing the energy content and high-frequency energy release rate of these events to a global average of the ratio between high-frequency energy release rate and its cumulative broad-band energy, we find that the Tohoku-Oki earthquake is relatively deficient in energy rate relative to other observed megathrust earthquakes. This result is analogous to what we found for the Sumatran 2004 earthquake, and similar to smaller tsunami earthquakes, but contrasts other MW 8.5 and larger earthquakes including the 2010 Chile and the 2005 Sumatra events, which did not create substantial transoceanic tsunamis. The slow energy growth observed in the 2011 Tohoku-Oki and 2004 Sumatran earthquakes, we argue, is due to slowed rupture in the shallow megathrust. Here, we will also detail how this event performed in the Georgia Tech real-time earthquake energy calculation program RtErg, and discuss its utility for identifying future such events.