Rupture process at the beginning of the 2007 Chuetsu-oki, Niigata, Japan, earthquake

Abstract

The rupture process at the beginning stage of the 2007 Chuetsu-oki, Niigata, Japan, earthquake (M W 6.6) is investigated by analyzing P-wave records from local strong-motion stations. The P-wave portion of the nearsource strong-motion records shows about 2 s of small but increasing amplitude arrival (so-called "initial rupture phase") followed by the onset of the main energy release ("main rupture phase"). Two issues are addressed in this paper: (1) where the initial rupture process occurred and (2) where the seismic energy corresponding to the main rupture phase was released at the primary stage of the main rupture. The first issue is addressed by locating the main rupture onset position, and the second issue is then approached by introducing a method for mapping the wave energy onto plausible fault planes. Eventually, the following were revealed. The rupture initiated and propagated on the NW-dipping plane, which is a nodal plane of the focal mechanism solution. At 2.1 s after rupture initiation the subsequent main rupture started at a position of approximately 4 km away, southwestward and updipward from the hypocenter. The main rupture at this stage has two possible rupture planes: the same plane as the initial rupture plane, and the conjugated plane, which shares the main rupture onset point with the initial rupture plane. Although it is difficult to determine which plane was actually ruptured at the primary stage of the main rupture, we found that the possible areas radiating strong wave energy on the two possible planes, which could correspond to the first asperity of this earthquake, are located between the hypocenter and the Kashiwazaki-Kariwa nuclear power plant.

High‐Resolution Fault‐Rupture Imaging by Combining a Backprojection Method With Binarized MUSIC Spectral Image Calculation

“…Additionally, various types of seismic waves can be used in BP. Some studies have used P‐waves (e.g., Takenaka et al., 2009), S‐waves (e.g., Festa & Zollo, 2006), and Rayleigh waves (e.g., Roten et al., 2012). Not only direct waves, but also various converted phases, such as sP waves (e.g., Jian et al., 2017), PP and PKP waves (e.g., Sufri et al., 2010), and PKIKP waves (e.g., Koper et al., 2012) have been used.…”

“…Various studies have attempted to obtain a high‐resolution seismic source image while suppressing noise. Some of these methods include correction of the travel time for the seismic source location (Ishii et al., 2005) or for the seismic source area using Kriging (Palo et al., 2014), travel time correction with aftershock data (Meng et al., 2016), the use of the travel time relative to the hypocenter (Takenaka et al., 2009; Yamamoto & Takenaka, 2006), the use of the travel time from a reference station (Maercklin et al., 2012), and the use of the travel time calculated with a 3‐D velocity structure model (Liu et al., 2017; Song & Ge, 2019).…”

“…BP has been applied to global earthquakes with a wide range of epicentral distances (e.g., Ishii et al., 2005; Kiser & Ishii, 2012; Liu et al., 2017; Melgar et al., 2016; Okuwaki et al., 2014; Walker et al., 2005; Walker & Shearer, 2009; Wang & Mori, 2011), as well as for regional earthquake analysis (e.g., Meng, Ampuero, Sladen, & Rendon, 2012; Wang, Kawakatsu, et al., 2016; Yang et al., 2020; Zhang & Ge, 2010) and local earthquake analysis (e.g., Evangelidis & Kao, 2014; Festa & Zollo, 2006; Honda et al., 2008; Pulido et al., 2008; Takenaka et al., 2009). BP has also been applied to various types of earthquakes, including subduction zone earthquakes (e.g., Ishii et al., 2005; Kiser & Ishii, 2012; Melgar et al., 2016), inland earthquakes (e.g., Allmann & Shearer, 2007; Jian et al., 2017; Liu et al., 2017; Walker & Shearer, 2009), long‐period volcanic earthquakes (e.g., Haney, 2014; Hendriyana & Tsuji, 2019), and tremors in subduction zones (e.g., Ghosh et al., 2012; Kao et al., 2005).…”

Dynamic rupture of crosscutting faults: A possible rupture process for the 2007 Mw 6.6 Niigata‐ken Chuetsu‐Oki earthquake

“…The SE‐dipping fault was found to have released a seismic moment that was about four times that released by the NW‐dipping conjugate fault [ Nishimura et al , 2010]. Recently, Takenaka et al [2009], using the initial rupture phase of the P wave portion, demonstrated that the main shock rupture initiated and propagated on the NW‐dipping plane along the dip from the depth to the shallow part. This seismological evidence suggests the sequential or simultaneous rupture of the two crosscutting conjugate fault planes.…”