Abstract:The slip-rates on the northern extent of Itoigawa-Shizuoka tectonic line (ISTL) are estimated based on seismic reflection profiles, drill core data and analysis of tectonic geomorphology. The ISTL is a major tectonic line that passes through the Honshu Island of Japan, and its northern and central segments form an active fault system characterized by high slip-rates. In the Kamishiro basin, near the northern end of the ISTL active fault system, the rate of net slip is estimated to be 4.4-5.4 m/kyr over the las… Show more
“…The northernmost segment of the ISTL, the Kamishiro fault, has been shown to be an active thrust fault (Sato et al, 2004;Takeda et al, 2004). On the other hand, the Otari-Nakayama fault, which runs parallel to the Kamishiro and East Matsumoto Basin faults, shows no geomorphological evidence of late Quaternary activity (Matsuta et al, 2004;Ueki, 2008).…”
A modern digital seismic network, with many stations optimally distributed on the earthquake causative seismic zone, enables detection of very low magnitude earthquakes and determination of their source parameters. It is essential to associate to such kind of networks procedures to analyze the huge amount of continuously recorded data for monitoring the space-time-magnitude evolution of natural and/or induced seismicity. Hence, the demand for near-real-time, automated data collection and analysis procedures for assisting seismic network operators in carrying out microearthquake monitoring is growing. In response to this need, we designed a computational software platform, TREMOR, for fast and reliable detection and characterization of seismicity recorded by a dense local seismic network. TREMOR integrates different open-source seismological algorithms for earthquake signal detection, location, and source characterizations in a fully automatic workflow. We applied the platform in play-back mode to the continuous waveform data recorded during 1 month at the Japanese Hi-net seismic network in the Nagano region (Japan) and compared the resulting catalog with the Japan Meteorological Agency bulletin in terms of number of detections, location pattern and magnitudes. The results show that the completeness magnitude of the new seismic catalog decreased by 0.35 units of the local magnitude scale and consequently the number of events increased by about 60% with respect to the available catalog. Moreover, the fault plane solutions resulted coherent with the stress regime of the region, and the Vp/Vs ratio well delineated the main structural features of the area. According to our results, TREMOR has shown to be a valid tool for investigating and studying earthquakes, especially to identify and monitor natural or induced micro-seismicity.
“…The northernmost segment of the ISTL, the Kamishiro fault, has been shown to be an active thrust fault (Sato et al, 2004;Takeda et al, 2004). On the other hand, the Otari-Nakayama fault, which runs parallel to the Kamishiro and East Matsumoto Basin faults, shows no geomorphological evidence of late Quaternary activity (Matsuta et al, 2004;Ueki, 2008).…”
A modern digital seismic network, with many stations optimally distributed on the earthquake causative seismic zone, enables detection of very low magnitude earthquakes and determination of their source parameters. It is essential to associate to such kind of networks procedures to analyze the huge amount of continuously recorded data for monitoring the space-time-magnitude evolution of natural and/or induced seismicity. Hence, the demand for near-real-time, automated data collection and analysis procedures for assisting seismic network operators in carrying out microearthquake monitoring is growing. In response to this need, we designed a computational software platform, TREMOR, for fast and reliable detection and characterization of seismicity recorded by a dense local seismic network. TREMOR integrates different open-source seismological algorithms for earthquake signal detection, location, and source characterizations in a fully automatic workflow. We applied the platform in play-back mode to the continuous waveform data recorded during 1 month at the Japanese Hi-net seismic network in the Nagano region (Japan) and compared the resulting catalog with the Japan Meteorological Agency bulletin in terms of number of detections, location pattern and magnitudes. The results show that the completeness magnitude of the new seismic catalog decreased by 0.35 units of the local magnitude scale and consequently the number of events increased by about 60% with respect to the available catalog. Moreover, the fault plane solutions resulted coherent with the stress regime of the region, and the Vp/Vs ratio well delineated the main structural features of the area. According to our results, TREMOR has shown to be a valid tool for investigating and studying earthquakes, especially to identify and monitor natural or induced micro-seismicity.
“…Slip rates on different fault segments along the ISTL active fault system vary from 1.5 to 3.3 mm/a on the northern segment, the Kamishiro Fault (Research Group for Active Faults of Japan, RGAFJ 1980, 1991; Imaizumi et al 1997; Okumura et al 1998; Matsuta et al 2001, 2004), which is the target segment in this study, to 5–14 mm/a on the central–southern segment (Ikeda and Yonekura 1986; Okumura 2001), and 5–8 mm/a on the southernmost segment (Lin et al 2013a). Thrust slip rates of up to ~14 mm/a along the ISTL active fault system are the highest onland thrust fault slip rates reported in Japan (Research Group for Active Faults of Japan, RGAFJ 1980, 1991).…”
Section: Tectonic Settingmentioning
confidence: 99%
“…4 ). The geological and seismic reflection data show that the Kamishiro Fault cuts late Pleistocene-Holocene sedimentary strata (Research Group for Active Faults of Japan, RGAFJ 1980 , 1991 ; Matsuta et al 2001 , 2004 ; Okumura et al 1998 ). Fig.…”
Section: Trench Excavation and Outcrop Exposurementioning
The Mw 6.2 (Mj 6.8) Nagano (Japan) earthquake of 22 November 2014 produced a 9.3-km long surface rupture zone with a thrust-dominated displacement of up to 1.5 m, which duplicated the pre-existing Kamishiro Fault along the Itoigawa–Shizuoka Tectonic Line (ISTL), the plate-boundary between the Eurasian and North American plates, northern Nagano Prefecture, central Japan. To characterize the activity of the seismogenic fault zone, we conducted a paleoseismic study of the Kamishiro Fault. Field investigations and trench excavations revealed that seven morphogenic paleohistorical earthquakes (E2–E8) prior to the 2014 Mw 6.2 Nagano earthquake (E1) have occurred on the Kamishiro Fault during the last ca. 6000 years. Three of these events (E2–E4) are well constrained and correspond to historical earthquakes occurring in the last ca. 1200 years. This suggests an average recurrence interval of ca. 300–400 years on the seismogenic fault of the 2014 Kamishiro earthquake in the past 1200 years. The most recent event prior to the 2014 earthquakes (E1) is E2 and the penultimate and antepenultimate faulting events are E3 and E4, respectively. The penultimate faulting event (E3) occurred during the period of AD 1800–1400 and is associated with the 1791 Mw 6.8 earthquake. The antepenultimate faulting event (E4) is inferred to have occurred during the period of ca. AD 1000–700, likely corresponding to the AD 841 Mw 6.5 earthquake. The oldest faulting event (E8) in the study area is thought to have occurred during the period of ca. 5600–6000 years. The throw rate during the early Holocene is estimated to be 1.2–3.3 mm/a (average, 2.2 mm/a) with an average amount of characteristic offset of 0.7–1.1 m produced by individual event. When compared with active intraplate faults on Honshu Island, Japan, these slip rates and recurrence interval estimated for morphogenic earthquakes on the Kamishiro Fault along the ISTL appear high and short, respectively. This indicates that present activity on this fault is closely related to seismic faulting along the plate boundary between the Eurasian and North American plates.
“…Seismic reflection profiling surveys were conducted by geomorphologists primarily to test the hypothesis given by analytical study of tectonic landform evolution mentioned in section 2.2 (Ishiyama et al 1999;Matsuta et al 2004;Sato et al 2004;Imaizumi and Sato 2005;Kagohara et al 2006, Figure 4). Based on these data, the grouping of faults corresponding to an earthquake and the geological evolution of faults were discussed.…”
Section: Seismic Reflection Profiling Of Active Faultsmentioning
Tectonic geomorphology has played important roles in active fault studies in Japan. Following large historical earthquakes, the concept of active fault was formulated and detailed information has rapidly accumulated. This paper reviews the progress of active fault studies in Japan since the 1980s. The period 1980 to 1994 can be regarded as the matured period of active fault studies during seismic calm. The studies conducted during this period are categorized into the following: 1) excavation studies of active faults, 2) analytical studies of tectonic landform evolution based on dislocation models, 3) chronological studies supported by the development of age determination techniques, and 4) studies quantifying the rate of crustal deformation. In 1995, the Great Kobe Earthquake occurred. The earthquake triggered a seismically active period in Japan, and the active fault has become an important issue in disaster mitigation. The research in the decade after 1995 can be summarized as follows: 1) intensive investigations of active faults, 2) detailed large-scale mapping, 3) seismic reflection profiling, 4) long-term forecasts of earthquakes, 5) careful study of flexural deformation, and 6) overseas research on large destructive earthquakes. Then, the period since 2005 has witnessed the rediscovery of active faults, with research considering 1) the relations between the large earthquakes which often occurred in this period and their seismogenic active faults, 2) precise distribution of active faults, 3) the relations between active tectonics and geodetical movement, 4) the relations between interplate earthquakes and submarine active faults, and 5) the difficult problems of prevention against infrequent disasters like the 2011 Great East Japan Earthquake. Additionally, since around 2006, some nuclear power plants have faced problems associated with active faults because some active faults had been overlooked or ignored in the seismic design of these plants. Active fault research now bears greater social responsibility.
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