Aftershock observation of the Noto Hanto earthquake in 2007 using ocean bottom seismometers

Yamada, Tomoaki; Mochizuki, Kimihiro; Shinohara, Masanao; Kanazawa, Toshihiko; Kuwano, A.; Nakahigashi, Kazuo; Hino, Ryota; Uehira, Kenji; Yagi, Takeo; Takeda, Naoto; Hashimoto, Shinichi

doi:10.1186/bf03352860

Cited by 13 publications

(4 citation statements)

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“…It is widely known that an ocean bottom seismometer (OBS) observation is essential to obtain a high-resolution aftershock distribution associated with large earthquakes that occurred in the marine environment (e.g., Shinohara et al, 2004;Sakai et al, 2005;Yamada et al, 2005). In addition, a spatially dense OBS observation is also necessary for a precise distribution of aftershocks occurring near a coast line be- cause a seismic network must cover a whole source region (Uehira et al, 2006;Yamada et al, 2008). Nine days after the mainshock, we started the aftershock observation using pop-up type OBSs in order to obtain detailed aftershock lateral and depth distributions of the 2007 Chuetsu-oki Earthquake.…”

Section: Introductionmentioning

confidence: 99%

Precise aftershock distribution of the 2007 Chuetsu-oki Earthquake obtained by using an ocean bottom seismometer network

et al. 2008

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The Chuetsu-Oki Earthquake occurred on July 16, 2007. To understand the mechanism of earthquake generation, it is important to obtain a detailed seismic activity. Since the source region of the 2007 Chuetsu-oki Earthquake lies mainly offshore of Chuetsu region, a central part of Niigata Prefecture, it is difficult to estimate the geometry of faults using only the land seismic network data. A precise aftershock distribution is essential to determine the fault geometry of the mainshock. To obtain the detailed aftershock distribution of the 2007 Chuetsu-oki Earthquake, 32 Ocean Bottom Seismometers (OBSs) were deployed from July 25 to August 28 in and around the source region of the mainshock. In addition, a seismic survey using airguns and OBSs was carried out during the observation to obtain a seismic velocity structure below the observation area for precise hypocenter determination. Seven hundred and four aftershocks were recorded with high spatial resolution during the observation period using OBSs, temporally installed land seismic stations, and telemetered seismic land stations and were located using the double-difference method. Most of the aftershocks occurred in a depth range of 6-15 km, which corresponds to the 6-km/s layer. From the depth distribution of the hypocenters, the aftershocks occurred along a plane dipping to the southeast in the whole aftershock region. The dip angle of this plane is approximately 40• . This single plane with a dip to the southeast is considered to represent the fault plane of the mainshock. The regions where few aftershocks occurred are related to the asperities where large slip is estimated from the data of the mainshock. The OBS observation is indispensable to determine the precise depths of events which occur in offshore regions even close to a coast.

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Section: Introductionmentioning

confidence: 99%

Precise aftershock distribution of the 2007 Chuetsu-oki Earthquake obtained by using an ocean bottom seismometer network

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“…Consequently, the interpretations presented in this paper will focus mainly on the velocity structures at land cross-sections from Y = −3 km to +16 km. In future studies, model resolutions beneath the ocean will be improved through an integration of data retrieved from ocean bottom seismometers deployed off the west coast of the Noto Peninsula (Yamada et al, 2007). Figure 2 shows the P-wave velocity (V p ) and the ratio of V p to V s along seven cross-sections perpendicular to the fault strike along relocated aftershocks within ±1.5 km from the section.…”

Section: Resultsmentioning

confidence: 99%

Three-dimensional velocity structure in the source region of the Noto Hanto Earthquake in 2007 imaged by a dense seismic observation

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The velocity structure and accurate aftershock distributions of the Noto Hanto Earthquake in 2007 (thrust type) are elucidated by inverting the arrival times from 917 aftershocks using double-difference tomography. P-wave velocity (V p ) of the hanging wall in the southeast appears to be higher than that of the footwall in the northwest, and the high-V p body of the hanging wall has a relatively high V p /V s ratio. Conversely, the low-V p body in the footwall appears to have a low V p /V s ratio at depths greater than 3 km. Aftershocks associated with the mainshock fault are roughly distributed along this velocity boundary between the hanging wall and footwall. Near-surface thin layers with significantly low V p and high V p /V s are imaged in a northwest direction from the mainshock epicenter. A likely explanation is that the mainshock fault plane was reactivated as a reverse fault in terms of the inversion tectonics due to the crustal shortening which initiated from the late Miocene. Both the mainshock hypocenter and the vertical alignment of aftershocks beneath it are located in the low-V p and low-V p /V s zones, indicating the potential presence of water-filled pores. Crustal stretching and shortening in and around the Noto Peninsula have created complex structures, including weak high-dip angle faults, almost vertical faults, and low velocity zones, which can potentially affect the seismic activities around the source region.

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“…This stress change is estimated to have been caused by variation in the dip angle of the subducting Pacific plate. Recently, the 2004 Chuetsu Earthquake (Sakai et al 2005), the 2007 Noto-Hanto Earthquake (Yamada et al 2008), and the 2007 Chuetsuoki Earthquake (Shinohara et al 2008) occurred in and around the NKTZ. Therefore precise seismic activity which may be induced by the large strain rate should be understood.…”

Section: Deployment Of the First System To The Japan Seamentioning

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New compact ocean bottom cabled seismometer system deployed in the Japan Sea

et al. 2013

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The Japanese islands are positioned near the subduction zones, and large earthquakes have repeatedly occurred in marine areas around Japan. However, the number of permanent earthquake observatories in the oceans is quite limited. It is important for understanding generation of large earthquakes to observe seismic activities on the seafloor just above these seismogenic zones. An ocean bottom cabled seismometer (OBCS) is the best solution because data can be collected in real-time. We have developed a new compact OBCS system. A developed system is controlled by a microprocessor, and signals from accelerometers are 24-bit digitized. Clock is delivered from the global positioning system receiver on a landing station using a simple dedicated line. Data collected at each cabled seismometer (CS) are transmitted using standard Internet Protocol to landing stations. The network configuration of the system adopts two dual methods. We installed the first practical OBCS system in the Japan Sea, where large earthquakes occurred in past. The first OBCS system has a total length of 25 km and 4 stations with 5 km interval. Installation was carried out in August 2010. The CSs and single armored optical submarine cable were buried 1 m below the seafloor to avoid a conflict with fishing activity. The data are stored on a landing station and sent to Earthquake Research Institute, University of Tokyo by using the Internet. After the installation, data are being collected continuously. According to burial of the CSs, seismic ambient noises are smaller than those observed on seafloor.

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Aftershock observation of the Noto Hanto earthquake in 2007 using ocean bottom seismometers

Cited by 13 publications

References 8 publications

Precise aftershock distribution of the 2007 Chuetsu-oki Earthquake obtained by using an ocean bottom seismometer network

Precise aftershock distribution of the 2007 Chuetsu-oki Earthquake obtained by using an ocean bottom seismometer network

Three-dimensional velocity structure in the source region of the Noto Hanto Earthquake in 2007 imaged by a dense seismic observation

New compact ocean bottom cabled seismometer system deployed in the Japan Sea

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