The 2011 M9.0 Tohoku (Japan) Earthquake: Insights from Drilling the Megathrust

The 2011 M9.0 Tohoku (Japan) Earthquake: Insights from Drilling the Megathrust

On March 11, 2011, the subduction plate boundary under northern Japan ruptured in a M9.0 megathrust earthquake. The earthquake rupture displayed some very unusual characteristics. The offset between the overriding and subducting plates was measured as ~60 m at the seafloor, more than twice the previous record for displacement in a single event! This great displacement, along with slowing of the rupture as the earthquake grew toward the surface, contributed to the production of a very large tsunami.

One year after the earthquake, the drilling vessel Chikyu sailed to the Japan Trench with 27 scientists from 14 countries to drill through the seafloor to sample the plate boundary fault (International Ocean Discovery Program Expedition 343). We recovered geophysical logs, thermal measurements, and core samples of the accretionary wedge, the downgoing Pacific Plate sediments, and the amazingly thin and slippery megathrust clays. My role on the expedition was “XCT Watchdog”, examining X-ray CT scans of the core as it came on board the ship to identify important deformation structures and distribute samples to the other specialist teams.

In this talk I will describe the M9.0 earthquake and explain how it was different than most of the M9.0 earthquakes of the 20th and 21st centuries. I will show some of the laboratories on D/V Chikyu and explain how science is done at sea on a big drilling vessel. Finally, I will show the data collected on the expedition and present our explanation for the unusual Tohoku Earthquake.

Speaker: Christie Rowe

McGill University

I am from northern California, my first pet rock was an actinolite-talc schist and I still have it. I was 11 when the M6.9 Loma Prieta Earthquake suddenly impressed on me that humans are small and temporary and thereby started me on the path to becoming a geologist. I was a mediocre student of great teachers at Smith College (BA 2000) and UC Santa Cruz (PhD 2007). I was a lecturer at University of Cape Town 2006-2009 and had a chance there to experiment (in research and teaching) and see lots of the world's greatest rocks. I left Cape Town to postdoc in a seismology group to learn everything I could about earthquakes and granular flow, but I mostly learned how to speak to earthquake seismologists. Since 2011 I have been a prof at McGill and the Wares Faculty Scholar in Economic Geology. In addition to earthquake geology and fault mapping, I work on the relationships between faults and ore deposits (especially gold), soft sediment deformation, X-ray diffraction, and rock mechanics. At McGill I teach an intro field methods course, field school, structural geology, and tectonics.

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