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Crustal seismogenic layer at active faults inferred by background seismicity and temperature data in Japan

Makoto Matsubara, & Tomoko E. Yano

Published August 13, 2018, SCEC Contribution #8409, 2018 SCEC Annual Meeting Poster #067

The lower limit of seismogenic layer within the crust relates to the maximum size of earthquakes caused by the active fault. We used the index “D95”, the depth above which 95 % of the whole crustal earthquakes occurred from the surface, to define the lower limits of the crustal seismogenic layer. We verify D95 for particular earthquakes after 2001 with magnitude larger than 6.5 by comparison with several parameters such as, the actual main shock hypocenter depth, their aftershocks, main slip region on the fault, and depth of the temperature as 250, 300, and 450 degrees in Celsius.

We estimated D95 with the catalog in which we relocated hypocenters between 2001 and 2012 from the NIED Hi-net catalog with Double-Difference method (Waldhauser and Ellsworth, 2000) for high resolved hypocenter locations (Depth <40 km, M>0.0) (JUICE catalog, Yano et al. 2017). Events with M>1.5 were chosen to satisfacty the Gutenberg-Richter magnitude-frequency relation. To calculate D95 was the same as Matsubara and Sato (2015). We estimated depths where the crustal temperature reaches 250, 300, and 450 degrees from heat flux (Matsumoto, 2007; Sakagawa et al., 2005) by using the steady-state, one-dimensional, heat conduction equation with an exponential decrease in the radioactivity heat generation introduced in Tanaka (2004).

Our result, D95, located under the deepest boundary of majority of aftershocks and main coseismic slip regions for many large. Except the deep aftershocks of the 2016 Kumamoto earthquake penetrated about 5 km deeper than the D95. We concluded that they occurred within the brittle-ductile transition zoon owing to too high Vp as 7.4 km/s for crustal brittle layer with temperature between 300 and 400 degrees. We also looked at the temperature around the volcanic zone such as Iwate-Miyagi Inland earthquake since the D95 is 10 km in spite of the D400 as 5 km.

Key Words
seismogenic zone, D95, D400deg

Matsubara, M., & Yano, T. E. (2018, 08). Crustal seismogenic layer at active faults inferred by background seismicity and temperature data in Japan. Poster Presentation at 2018 SCEC Annual Meeting.

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