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Stress patterns analysis about the seismic focal zone of the great Tohoku-Oki earthquake (M=9.0) in the Japan Trench subduction zone

Yongqing Zhang, Jiajia Yang, & Furen Xie

Published August 11, 2017, SCEC Contribution #7488, 2017 SCEC Annual Meeting Poster #227

The great Tohoku-Oki earthquake (M=9.0) which occurred on 11 March, 2011 and ruptured the plate boundary between the subducting Pacific plate and the overlying continental plate was the best scientifically recorded earthquake in Japan so far. Focal mechanisms were collected from NIED CMT solutions, and then we selected two rectangle regions to perform 2D stress inversion to acquire spatial and temporal stress patterns about the seismic focal zone in the Japan Trench subduction zone. Our results showed that: before the main shock, it could be inferred from the spatial distribution images of stress field that stress state in subduction zone was roughly uniform in space. P-axes, σ_1-axes and SHmax-axes almost plunged with low angle(<30°) in the direction of plate convergence, and the plunge angles of P-axes as well as σ_1-axes away from the source region and at east side of the Japan Trench were generally bigger than those in the source region. Meanwhile, it was found that, 8 years before the main shock, the stress field at northwest side of the source region (off the Miyagi Prefecture) was obviously disturbed by the 2003 Miyagi earthquake (MW=7.0) with the trend of σ_1-axes deflecting clockwise nearly 150° to 180° and then returned to its previous state. Nevertheless, there was no significant change of stress state elsewhere before the main shock, which may be related to the precursory sliding of the main shock fault at deep part. After the main shock, the stress field away from the source region had no evident change, while the change of the stress state in and around the source region was remarkable. Stress axes including P-axes and σ_1-axes plunged with big angles (>60°) in the direction of plate convergence, and SHmax-axes clockwise rotated nearly 60° to 90° in the source region and paralleled to the trench axis around the Japan trench. This study showed the characteristics of stress field variation before great earthquakes in the form of temporal and spatial images and reflected the interaction between structure and earthquakes in the seismogenic process of great earthquakes, which is very significant for understanding the seismogenic process of great earthquakes.

Key Words
The great 2011 Tohoku-Oki Earthquake (M=9.0), the Japan Trench, Subduction zone, Focal mechanism, Stress inversion

Citation
Zhang, Y., Yang, J., & Xie, F. (2017, 08). Stress patterns analysis about the seismic focal zone of the great Tohoku-Oki earthquake (M=9.0) in the Japan Trench subduction zone. Poster Presentation at 2017 SCEC Annual Meeting.


Related Projects & Working Groups
Stress and Deformation Over Time (SDOT)