Cutoff depth and coseismic slip zone for the large earthquake along the Sea of Japan

Makoto Matsubara, Tomoko E. Yano, & Tatsuya Ishiyama

Published August 12, 2021, SCEC Contribution #11331, 2021 SCEC Annual Meeting Poster #199

The subduction of the Pacific (PAC) plate from the east makes Japanese Islands under compressional stress. The cutoff depth of the seismogenic zone (D90) is important to estimate the maximum size of the earthquake with the active faults. We relocate hypocenters with three-dimensional seismic velocity (3D) structure using airgun and estimate the cutoff depth of seismogenic zone for the crustal events beneath Sea of Japanese.

We relocated 1,918,174 events from October 2000 to December 2019 within 120-150E, 20-50N with 3D structure. We selected events with depths of 0-25 km to be considered as those related to the active faults. We investigated the index D90 as the lower limits of the seismogenic layer defined as the depth above which 90 % of the whole crustal events occurred from the surface. The size of area in which we count earthquake is +/-0.1° in case of focusing the active faults and 0.20° in case of focusing the area.

We focus four large earthquakes, 2005 West Off Fukuoka prefecture, 2007 Noto Peninsula, 2007 Chuetsu-oki, and 2019 Off Yamagata earthquakes. We calculate D90 for each earthquake using the earthquake catalog before the mainshock. Hypocenters determined with 3D structure are shifted to shallower where the shallow low-velocity zones are resolved such as beneath the hypocenters of 2007 Chuetsu-oki and 2019 Off Yamagata earthquakes, however those are shifted to deeper where the shallow zone are not resolved such as 2005 West Off Fukuoka prefecture and 2007 Noto Hanto earthquake. Hypocenter of the 2007 Chuetsu-oki earthquake is at depth of 9 km and coseismic slip zone reached 15 km depth. These depths are extremely shallower than D90 as 25 km. The rupture area of the 2019 Off Yamagata prefecture earthquake reached 13 km depth and is above the D90 as 14 km. The hypocenter of the 2007 Noto Hanto earthquake is at 11 km depth and fault zone was estimated to 12 km. D90 estimated with hypocenters determined by 1D structure is 11 km however, D90 estimated with hypocenters determined by 3D structure is 12 km. D90 with 3D structure is below the fault zone. The hypocenter of the 2005 West Off Fukuoka prefecture earthquake is at 9 km depth and rupture zone is above the hypocenter. D90 is approximately 13 km

It indicates that the D90 estimated using hypocenters determined with 3D structure is important since D90 estimated using 1D structure partly located within the rupture zone.

Matsubara, M., Yano, T. E., & Ishiyama, T. (2021, 08). Cutoff depth and coseismic slip zone for the large earthquake along the Sea of Japan. Poster Presentation at 2021 SCEC Annual Meeting.

Related Projects & Working Groups