Seismological evidence of an active footwall shortcut thrust in the Northern Itoigawa–Shizuoka Tectonic Line derived by the aftershock sequence of the 2014 M 6.7 Northern Nagano earthquake

Panayotopoulos, Y.; Hirata, Naoshi; Hashima, Akinori; Iwasaki, Takaya; Sakai, Shin’ichi; Satō, Hiroshi

doi:10.1016/j.tecto.2016.04.019

Cited by 14 publications

(11 citation statements)

References 33 publications

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“…We use the 22 November 2014 M6.2 Northern Nagano earthquake (National Research Institute for Earth Science and Disaster [NIED] centroid location 36.689°N ; 137.890°E), which is located 3.9 km from the Hi‐net station HBAH, to establish the calibration factor. The earthquake ruptured to the surface, but the highest moment release was at 5‐km depth (NIED, Panayotopoulos et al, ). We choose the NIED tensor solution with a rake of 59°, a dip of 80°, and a strike of 358°.…”

Section: Setting Up Sources On the Istlmentioning

confidence: 99%

Strong Shaking Predicted in Tokyo From an Expected M7+ Itoigawa‐Shizuoka Earthquake

et al. 2018

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The Itoigawa-Shizuoka Tectonic Line (ISTL) is a major oblique left-lateral crustal fault that is expected to host M7+ events in the near future. Its proximity to the Kanto sedimentary basin poses a threat to the population of Metropolitan Tokyo. This study constructs ground motion predictions for scenario earthquakes on the ISTL using virtual earthquakes. We use the ambient seismic field to calculate the cross-correlation function that we assume proportional to the elastodynamic Green tensor between High-Sensitivity Seismograph network stations, which act as sources located above the ISTL, and the stations of the dense Metropolitan Seismic Observation network, which act as receivers in the Kanto Basin. We use the virtual earthquake approach , https://doi.org/10.1029Denolle, Dunham, et al., 2014, https://doi.org/10.1126 to predict ground motion from a suite of 270 kinematic sources and find that predicted ground motions are strong enough that nonlinear effects, which we do not model, may become important. We find that the shape of the sedimentary basin substantially alters the shaking by amplifying long-period ground motions as seismic waves refract at the basin edge. Additionally, we quantify ground motion variability due to source uncertainty, surmise that ground motions are lognormally distributed with regard to source uncertainties, and suggest that the variability is affected (locally either enhanced or reduced) by the basin shape. Finally, we find a coupling point between source and wave paths for epicentral locations on the ISTL that generates almost twice the shaking as equivalent unilateral ruptures, despite directivity orientation that would favor southward ruptures. Plain Language SummaryThe Itoigawa-Shizuoka Tectonic Line (ISTL) is a major crustal fault that is expected to host M7+ events in the future. Its proximity to the Kanto sedimentary basin poses a threat to the population of Metropolitan Tokyo. This study constructs ground motion predictions for scenario earthquakes on the ISTL using continuous recordings of the ambient seismic field. It takes advantage of dense seismic networks in Japan (High-Sensitivity Seismograph network and Metropolitan Seismic Observation network) to characterize seismic wave propagation in complex sedimentary basin structures. The results show that the sedimentary basin shape particularly affects the strength of the ground shaking and its variability. Overall, ground motion levels for a future ISTL earthquake are large and likely to affect tall infrastructures such as tall buildings and bridges. exhibit strong excitation of the first overtone mode at the basin edge. We elaborate on the source models and waveform synthetics constructed in laterally homogeneous medium to offer a discussion between ground motions from a simple and from a realistic 3-D medium. Calibration of the relative VEA amplitudes to absolute levels is performed using the Nagano earthquake. Finally, we examine and interpret our results for larger scenario earthquakes for both waveform predictions from t...

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Section: Setting Up Sources On the Istlmentioning

confidence: 99%

Strong Shaking Predicted in Tokyo From an Expected M7+ Itoigawa‐Shizuoka Earthquake

et al. 2018

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“…We mainly follow the overall fault geometry determined by Panayotopoulos et al (2016), which describes an ESE dipping primary fault, and then, we add the secondary structures of the steps and the branches (2) Assumed fault geometry and aftershock distribution. The red and green dots, respectively, represent the hypocentral locations of the aftershocks, which are closer to the primary fault and those deviated from it, respectively (after Panayotopoulos et al 2016). a The top view showing with the outlined fault traces (after Kato et al 1989;Nakata and Imaizumi 2002;Kondo et al 2008); the red and blue lines, respectively, denote surface traces of an active fault (Kamishiro fault) and a presumed geologic fault (Otari-Nakayama fault).…”

Section: The Modelmentioning

confidence: 99%

“…Interestingly, we can observe a geologically identified fault trace above Fault F, where the strike of this geologic fault coincides with that of Fault F (Kato et al 1989) although we do not assume the continuity each other. Other remarkable features are shallow low-angle branch fault (hereafter Fault B1) and a conjugate fault (hereafter Fault H2) assumed for the northern part, inferred from the aftershock distribution (Panayotopoulos et al 2016) and the field surveys . Fault B1 is merged to Fault B2 at depth, converged to the primary fault down dip.…”

Section: The Modelmentioning

confidence: 99%

“…4) indicates complex fault geometry exhibiting a significant variation along strike with the southern part forming a relatively simple and localized fault plane, while the northern part showing complicated geometry (Sakai et al 2015;Panayotopoulos et al 2016). While this observed geometrical difference between the north and the south is qualitatively understandable with the difference in the fault activity in the geomorphological timescale mentioned above, it is quite unclear how this geometrical complexity played roles in determining the resulting slip distribution and surface deformation.…”

Section: Introductionmentioning

confidence: 99%

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Dynamic rupture propagation on geometrically complex fault with along-strike variation of fault maturity: insights from the 2014 Northern Nagano earthquake

Ando

Imanishi

Panayotopoulos

et al. 2017

Earth Planets Space

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Understanding the effect of the complex fault geometry on the dynamic rupture process and discriminating it from the complexity originating from the rheological properties of faults, is an essential subject in earthquake science. The 2014 Northern Nagano earthquake, which occurred near the end zone of a major active fault system, provided unique observations that enabled us to investigate both the detailed geometrical fault structure and surface deformation patterns as well as the temporal sequence led up from a prominent foreshock activity. We first develop a geometrical fault model with a substantial variation along strike, and a model for the regional stress field, which is well constrained by the observations. This significant along-strike variation in fault geometry probably reflects the difference of fault maturity at the end zone of the complex fault system. We used this model in order to conduct a set of dynamic rupture simulations using the highly efficient spatiotemporal boundary integral equation method. Based on our simulations, we show that the observed surface deformation can be reasonably explained as the effect of the non-planar fault geometry with a number of branch faults and bends.

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“…Each event is linked to their neighbors through commonly observed phases with a maximum hypocentral separation between linked events of 5 km, resulting in 494,060 P wave pairs and 424,936 S wave pairs. The distribution of relocated hypocenters (Figure S4) generally agrees with those by Panayotopoulos et al [].…”

Section: Relocation Of Foreshock Sequencementioning

confidence: 99%

Non‐self‐similar source property for microforeshocks of the 2014 M_w 6.2 Northern Nagano, central Japan, earthquake

Imanishi

Uchide

2017

Geophysical Research Letters

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Foreshocks are considered as part of the preparation process for large earthquakes and, as such, can provide important constraints on earthquake generation. We examine the characteristics of the 4 day long foreshock sequence of the 2014 Northern Nagano earthquake (Mw 6.2) using seismograms recorded by a dense seismic observation network including data from a deep borehole closest to the foreshock region. The improved earthquake catalog shows a slow‐speed migration of the sequence toward the main shock hypocenter, implying possible slow‐slip transients which should have caused stress loading at the main shock hypocenter. An analysis of source spectra reveals that foreshocks for Mw < 1.5 display a weaker dependence of corner frequency on magnitude than expected for self‐similar scaling, suggesting that these microforeshocks can be regarded as small low‐frequency earthquakes. So far, we might have missed the expected weak low‐frequency preseismic signals, because they emerge only below a certain magnitude and are generally embedded in background noise.

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Seismological evidence of an active footwall shortcut thrust in the Northern Itoigawa–Shizuoka Tectonic Line derived by the aftershock sequence of the 2014 M 6.7 Northern Nagano earthquake

Cited by 14 publications

References 33 publications

Strong Shaking Predicted in Tokyo From an Expected M7+ Itoigawa‐Shizuoka Earthquake

Strong Shaking Predicted in Tokyo From an Expected M7+ Itoigawa‐Shizuoka Earthquake

Dynamic rupture propagation on geometrically complex fault with along-strike variation of fault maturity: insights from the 2014 Northern Nagano earthquake

Non‐self‐similar source property for microforeshocks of the 2014 M_w 6.2 Northern Nagano, central Japan, earthquake

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Seismological evidence of an active footwall shortcut thrust in the Northern Itoigawa–Shizuoka Tectonic Line derived by the aftershock sequence of the 2014 M 6.7 Northern Nagano earthquake

Cited by 14 publications

References 33 publications

Strong Shaking Predicted in Tokyo From an Expected M7+ Itoigawa‐Shizuoka Earthquake

Strong Shaking Predicted in Tokyo From an Expected M7+ Itoigawa‐Shizuoka Earthquake

Dynamic rupture propagation on geometrically complex fault with along-strike variation of fault maturity: insights from the 2014 Northern Nagano earthquake

Non‐self‐similar source property for microforeshocks of the 2014 Mw 6.2 Northern Nagano, central Japan, earthquake

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Non‐self‐similar source property for microforeshocks of the 2014 M_w 6.2 Northern Nagano, central Japan, earthquake