Structure and Composition of the Plate-Boundary Slip Zone for the 2011 Tohoku-Oki Earthquake

Abstract

The mechanics of great subduction earthquakes are influenced by the frictional properties, structure, and composition of the plate-boundary fault. We present observations of the structure and composition of the shallow source fault of the 2011 Tohoku-Oki earthquake and tsunami from boreholes drilled by the Integrated Ocean Drilling Program Expedition 343 and 343T. Logging-while-drilling and core-sample observations show a single major plate-boundary fault accommodated the large slip of the Tohoku-Oki earthquake rupture, as well as nearly all the cumulative interplate motion at the drill site. The localization of deformation onto a limited thickness (less than 5 meters) of pelagic clay is the defining characteristic of the shallow earthquake fault, suggesting that the pelagic clay may be a regionally important control on tsunamigenic earthquakes.

IODP workshop: tracking the Tsunamigenic slips across and along the Japan Trench (JTRACK)

“…LWD data and cores recovered from depths down to ∼ 840 m b.s.f. defined the location and composition of the plate boundary fault (Chester et al, 2013b;Kirkpatrick et al, 2015). Temperature data from the observatory installed during Expedition 343T and recovered 9 months later by R/V Kairei showed a thermal anomaly at the megathrust horizon, which was used to infer a very low dynamic friction coefficient of 0.08 (Fulton et al, 2013), consistent with lab measurements of the frictional properties of core samples at seismic slip velocities (Ujiie et al, 2013).…”

The damage is done: Low fault friction recorded in the damage zone of the shallow Japan Trench décollement

“…Geophysical measurements and core observations show the décollement is localized onto a layer of smectite-rich fault rock that is surrounded by a complex zone of deformation [Chester et al, 2013a[Chester et al, , 2013bKirkpatrick et al, 2015], typical of subduction faults generally [Rowe et al, 2013;Ujiie and Kimura, 2014]. Temperature measurements in the fault zone [Fulton et al, 2013], laboratory friction experiments on core samples from the décollement Sawai et al, 2014;Ikari et al, 2015;Remitti et al, 2015], and measurements of the anisotropy of magnetic susceptibility all suggest that the décollement at the JFAST study site is frictionally weak.…”

“…Temperature measurements in the fault zone [Fulton et al, 2013], laboratory friction experiments on core samples from the décollement Sawai et al, 2014;Ikari et al, 2015;Remitti et al, 2015], and measurements of the anisotropy of magnetic susceptibility all suggest that the décollement at the JFAST study site is frictionally weak. Here we take advantage of the Expedition 343 drill Chester et al, 2013b]. Earthquake epicenter denoted by red and white star.…”

Extreme hydrothermal conditions at an active plate-bounding fault

“…Drilling studies have taken place in response to earthquakes of M w = 6.9-9.0 in Japan, Taiwan, China and the USA 8,[10][11][12][18][19][20][21] , and the results do not reveal anomalous temperatures or fluid pressures (Fig. 1).…”