Recent Surface Faulting Events along the Northern Part of the Itoigawa-Shizuoka Tectonic Line -Trenching Survey of the Kamishiro Fault and East Matsumoto Basin Faults, Central Japan-

Okumura, Koji; Imura, Ryusuke; Imaizumi, Tsutomu; Togo, Masami; Sawa, Hiroshi; Mizuno, Kiyohide; Kariya, Yoshiharu; Saito, Eiji

doi:10.4294/zisin1948.50.appendix_35

Cited by 16 publications

(7 citation statements)

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“…Paleo-seismological studies on one of the most active segments of ISTL (Ikeda and Yonekura, 1986;Okumura et al, 1994) revealed unusual large displacement per one earthquake event (8.6-9.5 mm/year) and an unusual short recurrence time (1000 years). Based on these observations, fault system at ISTL is believed to have a potential of M8 earthquake.…”

Section: Geological Setting Of the Itoigawa-shizuoka Tectonic Linementioning

confidence: 99%

Mid-crustal electrical conductors and their correlations to seismicity and deformation at Itoigawa-Shizuoka Tectonic Line, Central Japan

Ogawa

Honkura

2014

Earth Planet Sp

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An active fault segment at the northern Itoigawa-Shizuoka tectonic line (ISTL), Central Japan, which will potentially cause M8-class intraplate earthquake, was imaged by wide-band magnetotellurics. Three parallel profiles across ISTL revealed along-strike variation of the resistivity structure. Three resistivity models commonly showed the thickening conductors in the upper crust to east of ISTL which imply the heavily folded Miocene sediments with maximum thickness of several kilometers. Thus the upper crustal structure seems two-dimensional throughout the segment. We found mid-crustal conductors, top of which correlate well with the cutoff depth of seismicity. The seismicity clusters mainly in the resistive crust that is underlain by the mid-crustal conductors. This implies the local distribution of fluids below the brittle-ductile boundary and suggests that the fluid migration into resistive zone is triggering earthquakes. However, the distribution of these mid-crustal conductors is not consistent with the strike of ISTL, but rather it is better correlated with the negative dilatation anomaly inferred from GPS. This suggests the weakening of the crust by the existence of fluids.

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Section: Geological Setting Of the Itoigawa-shizuoka Tectonic Linementioning

confidence: 99%

Mid-crustal electrical conductors and their correlations to seismicity and deformation at Itoigawa-Shizuoka Tectonic Line, Central Japan

Ogawa

Honkura

2014

Earth Planet Sp

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“…Northern and central parts of the ISTL are considered to be an active fault zone while the southern ISTL has ceased its activity (e.g. Okumura et al, 1998). The Matsumoto Basin west of the northern ISTL is filled with thick (>6 km) Quaternary sediments (Ikami et al, 1986).…”

Section: Itoigawa-shizuoka Tectonic Linementioning

confidence: 99%

“…The East Matsumoto-Basin Fault (hereafter called EMBF) in the northern ISTL is also active, having 3.0 mm/yr slip rate (Okumura et al, 1998). In spite of such large slip rates, no earthquake of magnitude 7 or larger is known to have occurred in this region for more than 1,000 years.…”

Section: Itoigawa-shizuoka Tectonic Linementioning

confidence: 99%

Crustal deformation around the northern and central Itoigawa-Shizuoka Tectonic Line

et al. 2014

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We established a dense permanent GPS array around the northern and central Itoigawa-Shizuoka Tectonic Line (ISTL) in order to study loading processes of inland active faults. 1-4 years observation has revealed concentrated deformation (about 0.3 ppm/yr) around the East Matsumoto-Basin Fault, an active fault along the ISTL, consistent with historic triangulation data. The deformation pattern is explained by dislocation models incorporating horizontal detachment fault with steady slip in the upper crust. However, deformation data alone cannot determine the model and there exist different possibilities. The vicinity of the Gofukuji fault is being deformed less in spite of the large long-term slip rate. These observations indicate that the deformation pattern is laterally heterogeneous along the ISTL. The two faults are considered to be loaded by different mechanisms.

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“…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%

Paleoseismic study of the Kamishiro Fault on the northern segment of the Itoigawa–Shizuoka Tectonic Line, Japan

et al. 2016

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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.

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Recent Surface Faulting Events along the Northern Part of the Itoigawa-Shizuoka Tectonic Line -Trenching Survey of the Kamishiro Fault and East Matsumoto Basin Faults, Central Japan-

Cited by 16 publications

References 0 publications

Mid-crustal electrical conductors and their correlations to seismicity and deformation at Itoigawa-Shizuoka Tectonic Line, Central Japan

Mid-crustal electrical conductors and their correlations to seismicity and deformation at Itoigawa-Shizuoka Tectonic Line, Central Japan

Crustal deformation around the northern and central Itoigawa-Shizuoka Tectonic Line

Paleoseismic study of the Kamishiro Fault on the northern segment of the Itoigawa–Shizuoka Tectonic Line, Japan

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