Fault plane of the 1964 Niigata earthquake, Japan, derived from relocation of the mainshock and aftershocks by using the modified joint hypocenter determination and grid search methods

Abstract

We relocated the mainshock and immediate aftershocks of the 1964 Niigata earthquake (M s 7.5) using both the modified joint hypocenter determination (MJHD), and the grid search (GS), methods to obtain their hypocenters and identify the fault plane of the mainshock. We used P-wave arrival times at 13 Japanese stations reported by the Japan Meteorological Agency (JMA). Firstly, we performed the MJHD method to select readings with high accuracies and to obtain station corrections that related to the lateral heterogeneity of the Earth's structure. Secondly, we performed the GS method by using only selected readings and assuming the station corrections. Based on the relocated hypocenters, we found that the mainshock and immediate aftershocks occurred along a plane striking N15• E and dipping 11• eastward. This result strongly suggests that one of the nodal planes of the mainshock, for which the strike and dip are N9• E and 34• , respectively, is preferable as the fault plane. When global stations are also used for relocations, the results confirm that the fault plane of the 1964 Niigata earthquake dips gently eastward. Therefore, we concluded that the fault plane of the 1964 Niigata earthquake is gently eastward-dipping.

Stress field in northeastern Japan and its relationship with faults of recent earthquakes

“…The estimated ST values in the EMJS and Tohoku inland areas in this study were compared with the actual fault planes and ST values estimated in previous studies (e.g., Hatori 1969;Satake and Abe 1983;Aida 1984Aida , 1989Satake 1985Satake , 1986Umino et al 1985Umino et al , 1998Kosuga et al 1986;Sato et al 1986;Nakanishi et al 1993;Sato 1993;Tanioka et al 1995;Okada et al 2003Okada et al , 2012Ohta et al 2008;Hurukawa and Harada 2013;Yoshida et al 2014Yoshida et al , 2016Earthquake Research Committee 2019;Fig. 15).…”

“…If there were duplicate events from both databases, the quality of the F-net moment tensor solution was also evaluated, and if its solution variance reduction was > 60, the F-net moment tensor solution was used in the stress inversion. Based on the brittleductile transition (e.g., Scholz 1988) and aftershock distribution of large-to-moderate size earthquakes in this area (e.g., Tanioka et al 1995;Okada et al 2003;Hurukawa and Harada 2013), earthquakes due to fault activities are presumed to occur at depths of approximately 0-30 km, hence this depth range was used in the present study.…”

“…1A), which may correspond to the eastern boundary of the contraction and uplifting of the Tohoku backbone range (e.g., Okada et al 2010). However, recent large earthquakes (e.g., the 1940 Shakotan-Oki earthquake [M jma 7.5], 1964 Niigata earthquake [M jma 7.5], and 2019 Yamagata-Oki earthquake [M jma 6.7]) are confirmed to have occurred on low dip angle with eastward-dipping fault plane, and this may be related to eastward incipient subduction of the oceanic lithosphere along the EMJS (Fukao and Furumoto 1975;Satake 1983;Hurukawa and Harada 2013; Earthquake Research Committee 2019; Fig. 1A).…”

Stress field in the northeastern Japan and its relationship with faults of recent earthquakes

“…Therefore, inversion tectonics is believed to occur, in which old normal faults (high-dip-angle fault planes) dip westward and act as reverse faults (Okamura et al, 1995). However, recent large earthquakes (e.g., the 1964 Niigata earthquake (M jma 7.5) and the 2019 Yamagata-Oki earthquake (M jma 6.7)) are con rmed to have occurred on a low-dip-angle plane with eastward dipping (Hurukawa and Harada, 2013; Earthquake Research Committee, 2019).…”