Marian E. Magee, Mark D. Zoback; Evidence for a weak interplate thrust fault along the northern Japan subduction zone and implications for the mechanics of thrust faulting and fluid expulsion. Geology ; 21 (9): 809–812. doi: https://doi.org/10.1130/0091-7613(1993)021<0809:EFAWIT>2.3.CO;2
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The complex distribution of aftershock focal mechanisms of the 1968 Tokachi-Oki earthquake is consistent with a best-fitting uniform stress tensor in which the minimum principal stress acts approximately perpendicular to the main-shock thrust plane. This implies low resolved shear stresses on the interplate thrust fault as well as low frictional fault strength, which can be explained by elevated pore pressure within a hydraulically sealed fault zone. After great subduction-zone earthquakes, episodic fluid flow may relieve the high fault-zone pore pressures via hydraulic fracturing along the main-shock thrust plane.