Horizontal stress orientations in the largest displacement area of the Mw9.0 Tohoku earthquake

Author(s): Lin, W.; Conin, M.; Moore, J. C.; Chester, F. M.; Nakamura, Y.; Anderson, L. M.; Mori, J. J.; Eguchi, N.; Toczko, S.
Integrated Ocean Drilling Program, Expedition 343, Japan Trench Fast Drilling Project, Tohoku
Author Affiliation(s): Primary:
Japan Agency for Marine-Earth Science and Technology, Kochi Institute, Kochi Pref., Japan
Other:
Centre de Recherche et d'Enseignement de Géosciences de l'Environnement, France
University of California at Santa Cruz, United States
Texas A&M University, United States
University of Leicester, United Kingdom
Kyoto University, Japan
Volume Title: AGU 2012 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2012; American Geophysical Union 2012 fall meeting, San Francisco, CA, Dec. 3-7, 2012. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: Integrated Ocean Drilling Program Expedition 343, Japan Trench Fast Drilling Project (JFAST), drilled three boreholes at Site C0019, located about 93 km seaward from the epicenter of the Tohoku-Oki earthquake mainshock and ∼5 km landward of the trench axis. At this site, Hole C0019B was dedicated to logging-while-drilling (LWD); Hole C0019E was cored to obtain samples of the accretionary prism and plate boundary fault; and Hole C0019D was drilled for installation of a temperature observatory. The borehole used for logging, C0019B, penetrated 850 meters below seafloor (mbsf) in a water depth of 6890 m. Borehole wall resistivity images clearly show drilling induced borehole breakouts from 46 to 813 mbsf. Breakouts are reliable indicators of the orientations of the current maximum and minimum horizontal stresses (SHmax and Shmin) and can be used to constrain stress magnitudes. The borehole passed through the plate boundary fault around 820 mbsf, the probable principal slip zone of the 2011 earthquake and no breakouts were observed below the fault. The azimuth of SHmax and its variability differ markedly in the shallow and deep parts of the borehole. In the shallow portion (Logging Unit I slope facies and Unit IIa wedge sediments), the azimuth is highly variable. Such diverse breakout orientations have not been previously recognized at subduction zones. One explanation could be that SHmax and Shmin are close in magnitude and the scattered distribution of horizontal stress orientations result from localized perturbations. This result suggests that the co-seismic release of tectonic stress in the shallow portion of the frontal prism was nearly complete. The azimuth of SHmax in the deeper portion (Unit IIb wedge sediments) had a preferred orientation in a northwest - southeast direction. This stress orientation is consistent with the plate convergence direction of 292°, and also roughly consistent with stress orientations at Ocean Drilling Program sites 1150 and 1151, which were drilled prior to the earthquake in 1999. We are trying to constrain the magnitude of the horizontal principal stress at the two depths where both breakout width and unconfined compressive strength are available. Combined with the vertical stress (SV) calculated from a sediment density profile, we can determine the type of stress regime at these depths.
Year of Publication: 2012
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 16 Structural Geology; 19 Geophysics, Seismology; Asia; Displacements; Earthquakes; Expeditions 343/343T; Far East; Faults; Honshu; IODP Site C0019; Integrated Ocean Drilling Program; Japan; Japan Trench; Japan Trench Fast Drilling Project; North Pacific; Northwest Pacific; Pacific Ocean; Tohoku-Oki earthquake 2011; West Pacific
Coordinates: N375619 N375620 E1435449 E1435447
Record ID: 2014070597
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