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

• Published in: Geology (Boulder) 2001-02, Vol.29 (2), p.183-186
• Main Authors: Moore, J. Casey, Saffer, Demian
• Format: Article
• Language: English
• Subjects: accretionary wedges; Asia; causes; cementation; clay mineralogy; clay minerals; coseismic processes; diagenesis; earthquakes; Far East; faults; fluid pressure; framework silicates; Geology; hanging wall; Honshu; isotherms; Japan; Kyushu; Leg 131; low-grade metamorphism; Marine; metamorphism; Muroto Peninsula; Nankaido earthquake 1946; North Pacific; Northwest Pacific; Ocean Drilling Program; Pacific Ocean; pressure solution; quartz; seismic zoning; seismicity; Seismology; sheet silicates; Shikoku; silica minerals; silicates; southwestern Japan; stress; subduction zones; temperature; thermal effects; transformations; uplifts; West Pacific
• ISSN: 0091-7613; 1943-2682
• DOI: 10.1130/0091-7613(2001)029<0183:ULOTSZ>2.0.CO;2

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.