Updip limit of the seismogenic zone beneath the accretionary prism of southwest Japan: An effect of diagenetic to low-grade metamorphic processes and increasing effective stress
- 1Department of Earth Sciences, University of California, Santa Cruz, California 95064, USA
- 2U.S. Geological Survey, Menlo Park, California 94025, USA, and Institute of Geophysics and Planetary Physics, University of California, Santa Cruz, California 95064, USA
Abstract
Off southwest Japan the seaward limit of coseismic displacement (or updip limit of the seismogenic zone) of the 1946 Mw 8.3 thrust earthquake reaches to 4 km depth and ∼40 km landward of the trench. This limit coincides with the estimated location of the 150 °C isotherm, and has been linked to changes in physical properties associated with the smectite to illite clay-mineral transition. Here we show that this limit correlates with a suite of diagenetic to low-grade metamorphic processes characterized by (1) declining fluid production and decreasing fluid pressure ratio (λ*) and (2) active clay, carbonate, and zeolite cementation and the transition to pressure solution and quartz cementation. These diagenetic to low-grade metamorphic changes cause the onset of velocity weakening during thrust faulting, an increase in effective stress, and strengthening of the hanging wall, which together combine to produce recordable earthquakes.
Footnotes
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- Accepted November 7, 2000.
- Received July 5, 2000.
- Revision received November 3, 2000.
- Geological Society of America
