Magnetotelluric transect across the Niigata‐Kobe Tectonic Zone, central Japan: A clear correlation between strain accumulation and resistivity structure

Yoshimura, Ryokei; Oshiman, Naoto; Uyeshima, Makoto; Toh, Hiroaki; Uto, Tomofumi; Kanezaki, H.; Mochido, Yuji; Aizawa, Katsuo; Ogawa, Yasuo; Nishitani, Tadashi; Sakanaka, Shin’ya; Mishina, Masaaki; Satoh, Hideyuki; Goto, Tada-nori; Kasaya, Takafumi; Yamaguchi, Satoru; Murakami, Hideki; Mogi, Toru; Yamaya, Yusuke; Harada, Makoto; Shiozaki, Ichiro; Honkura, Yoshimori; Koyama, Shigeru; Nakao, S.; Wada, Yasuo; Fujita, Yasuhito

doi:10.1029/2009gl040016

Cited by 30 publications

(42 citation statements)

References 32 publications

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“…The concept is similar to the hypothesis of Iio et al (2002) who assumed that the lower crust had a deformable weak zone. In addition, our results suggest that fluids supplied from conductive zones to nearby resistive zones can promote earthquake occurrences (e.g., Mitsuhata et al 2001;Ogawa et al 2001;Yoshimura et al (Yamashina and Murai 1975) are also overlain on the profiles. Because the hypocentral depths of these two earthquakes were not determined, they are plotted on both profiles.…”

Section: Discussionmentioning

confidence: 85%

“…Such complex tectonic settings suggest complex subsurface structures that may be related to the characteristic seismicity. Because electrical resistivity is sensitive to the presence of fluids, and subsequently the elasticity of the media, it is important to investigate how resistivity structures relate to earthquake generation Fujinawa et al 2002;Goto et al 2005;Guerer and Bayrak 2007;Wannamaker et al 2009;Yoshimura et al 2009;Ichihara et al 2011Ichihara et al , 2014Ichihara et al , 2016Ogawa et al 2014;Kaya et al 2013). To investigate the relationship between earthquakes and electrical resistivity structure, we gathered and analyzed the broadband (typically 0.003-10,000 s) magnetotelluric (MT) and telluric data, which resolve the resistivity structure from the surface to the depth of the upper mantle.…”

Section: Introductionmentioning

confidence: 99%

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Seismicity controlled by resistivity structure: the 2016 Kumamoto earthquakes, Kyushu Island, Japan

Aizawa

Asaue

Koike

et al. 2017

Earth Planets Space

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The M JMA 7.3 Kumamoto earthquake that occurred at 1:25 JST on April 16, 2016, not only triggered aftershocks in the vicinity of the epicenter, but also triggered earthquakes that were 50-100 km away from the epicenter of the main shock. The active seismicity can be divided into three regions: (1) the vicinity of the main faults, (2) the northern region of Aso volcano (50 km northeast of the mainshock epicenter), and (3) the regions around three volcanoes, Yufu, Tsurumi, and Garan (100 km northeast of the mainshock epicenter). Notably, the zones between these regions are distinctively seismically inactive. The electric resistivity structure estimated from one-dimensional analysis of the 247 broadband (0.005-3000 s) magnetotelluric and telluric observation sites clearly shows that the earthquakes occurred in resistive regions adjacent to conductive zones or resistive-conductive transition zones. In contrast, seismicity is quite low in electrically conductive zones, which are interpreted as regions of connected fluids. We suggest that the series of the earthquakes was induced by a local accumulated stress and/or fluid supply from conductive zones. Because the relationship between the earthquakes and the resistivity structure is consistent with previous studies, seismic hazard assessment generally can be improved by taking into account the resistivity structure. Following on from the 2016 Kumamoto earthquake series, we suggest that there are two zones that have a relatively high potential of earthquake generation along the western extension of the MTL.

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Section: Discussionmentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Seismicity controlled by resistivity structure: the 2016 Kumamoto earthquakes, Kyushu Island, Japan

Aizawa

Asaue

Koike

et al. 2017

Earth Planets Space

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“…However, heterogeneous structures beneath intraplate strike-slip faults observed by seismic tomography (e.g., Nakajima and Hasegawa 2007;Nakajima et al 2010) and magnetotelluric survey (e.g., Ogawa and Honkura 2004;Yoshimura et al 2009) suggest the existence of localized weak zones in the lower crust just below intraplate active faults (Iio et al 2002(Iio et al , 2004. The spatial resolution of these observations is insufficient to resolve the structures of such ductile shear zones.…”

Section: Introductionmentioning

confidence: 90%

Shear strain concentration mechanism in the lower crust below an intraplate strike-slip fault based on rheological laws of rocks

Zhang

Sagiya

2017

Earth Planets Space

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We conduct a two-dimensional numerical experiment on the lower crust under an intraplate strike-slip fault based on laboratory-derived power-law rheologies considering the effects of grain size and water. To understand the effects of far-field loading and material properties on the deformation of the lower crust on a geological time scale, we assume steady fault sliding on the fault in the upper crust and ductile flow for the lower crust. To avoid the stress singularity, we introduce a yield threshold in the brittle-ductile transition near the down-dip edge of the fault. Regarding the physical mechanisms for shear strain concentration in the lower crust, we consider frictional and shear heating, grain size, and power-law creep. We evaluate the significance of these mechanisms in the formation of the shear zone under an intraplate strike-slip fault with slow deformation. The results show that in the lower crust, plastic deformation is possible only when the stress or temperature is sufficiently high. At a similar stress level, ∼100 MPa, dry anorthite begins to undergo plastic deformation at a depth around 28-29 km, which is about 8 km deeper than wet anorthite. As a result of dynamic recrystallization and grain growth, the grain size in the lower crust may vary laterally and as a function of depth. A comparison of the results with constant and nonconstant grain sizes reveals that the shear zone in the lower crust is created by power-law creep and is maintained by dynamically recrystallized material in the shear zone because grain growth occurs in a timescale much longer than the recurrence interval of intraplate earthquakes. Owing to the slow slip rate, shear and frictional heating have negligible effects on the deformation of the shear zone. The heat production rate depends weakly on the rock rheology; the maximum temperature increase over 3 Myr is only about several tens of degrees.

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“…This value corresponds to the high strain rate in the NKTZ defined by Sagiya et al (2000), and its area seems plausible to the extent of the low seismic velocity anomaly in the lower crust (25 km depth) estimated by Nakajima & Hasegawa (2007). Yoshimura et al (2009) also indicate the extent of the NKTZ, which is located between the Ushikubi fault and the Takayama-Oppara fault zone by the MT analysis. Therefore, the high strain rate zone is identified as this approximately 50 km wide region in this area.…”

Section: Features Of the High Strain Rate Zonementioning

confidence: 96%

Strain accumulation process around the Atotsugawa fault system in the Niigata-Kobe Tectonic Zone, central Japan

Ohzono¹,

Sagiya²,

Hirahara³

et al. 2011

Geophysical Journal International

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S U M M A R YIn order to investigate the strain accumulation process around the Niigata-Kobe Tectonic Zone in central Japan, we estimate a precise GPS velocity field around a representative fault area, the Atotsugawa fault system. The velocity profiles obtained from two dense GPS arrays crossing the Atotsugawa fault demonstrate the existence of a laterally heterogeneous deformation pattern along the fault strike. The West Array suggests the possibility of surface fault creep, which disagrees with inferences gleaned from previous EDM measurements. High shear strain rate, which is calculated from wider velocity field, distributes around not only the Atotsugawa fault system, but also the Takayama-Oppara fault zone, which is located 50 km south from the Atotsugawa fault. In order to consider the effect of interaction between those active faults, we conduct a block-fault model analysis. Our block model consists of nine blocks and 33 fault segments. Relative motion between two blocks at the northern and southern ends of the fault system is calculated to be 9.9 mm yr −1 . The intervening region between these two blocks corresponds to the Niigata-Kobe Tectonic Zone with a strain rate of 0.2 ppm yr −1 . Slip deficit rates at the Atotsugawa, Ushikubi, and Takayama-Oppara fault zones are estimated to be 2.2, 3.9 and 2.3 mm yr −1 , respectively. Although the ratio of slip deficit rate (2.2 : 3.9 : 2.3 ≈ 1 : 2 : 1) of these three faults is similar to that of geological long-term slip rates (1 : 2 : 0.7), the magnitude of geodetic slip deficits is 30 per cent to 50 per cent larger than long-term slip rates. This systematic difference may be due to inelastic deformation of the crust in this region. Since the total slip deficit rate between the Ushikubi and the Takayama-Oppara fault zone is 8.4 mm yr −1 , about 85 per cent of the relative block motion, the deformation is mostly accommodated by elastic strain accumulation on these three faults.

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Magnetotelluric transect across the Niigata‐Kobe Tectonic Zone, central Japan: A clear correlation between strain accumulation and resistivity structure

Cited by 30 publications

References 32 publications

Seismicity controlled by resistivity structure: the 2016 Kumamoto earthquakes, Kyushu Island, Japan

Seismicity controlled by resistivity structure: the 2016 Kumamoto earthquakes, Kyushu Island, Japan

Shear strain concentration mechanism in the lower crust below an intraplate strike-slip fault based on rheological laws of rocks

Strain accumulation process around the Atotsugawa fault system in the Niigata-Kobe Tectonic Zone, central Japan

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