Hypocenters in the Nankai Trough Determined by Using Data from Both Ocean‐Bottom and Land Seismic Networks and a 3D Velocity Structure Model: Implications for Seismotectonic Activity

Nakamura, Takeshi; Kaneda, Yasufumi

doi:10.1785/0120140309

Cited by 19 publications

(15 citation statements)

References 43 publications

(68 reference statements)

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“…The largest residuals are found southeast off Kii Peninsula, near 137°E. This may be caused by postseismic deformation of the M w 7.2 and M w 7.4 earthquakes off Kii Peninsula on 26 September 2004, which was an intraslab event in the subducting plates (Nakano et al, 2015) (Fig. 3B).…”

Section: Resultsmentioning

confidence: 95%

Strain partitioning and interplate coupling along the northern margin of the Philippine Sea plate, estimated from Global Navigation Satellite System and Global Positioning System-Acoustic data

et al. 2018

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Southwest Japan is located in the subduction margin between the continental Amurian and oceanic Philippine Sea plates. Recent land GNSS (Global Navigation Satellite System) and offshore Global Positioning System-Acoustic geodetic measurements were used to clarify the deformation in and around these plate margins. We examined strain partitioning and interplate coupling using a block modeling approach on the observed velocities. Although the main plate boundaries are the Nankai Trough and Sagami trough, our results suggest that one-third of the relative plate motion between the two plates is accommodated by several block boundaries in the southeastern margin of the Amurian plate. The most active boundaries, with a slip rate of ≥8 mm/yr, cross southwest Japan from the Okinawa Trough through the Median Tectonic Line and Niigata Kobe tectonic zone, to the eastern margin of the Japan Sea. A subparallel boundary with a slip rate of 4-5 mm/yr is along the coastline of Japan. These two boundaries have a right-lateral shear motion that accommodates part of the interplate motion, with a boundary across the Korean Peninsula and Japan Sea. The slip partitioning results in an eastward decrease of relative block motion from 78 to 4 mm/yr along the Nankai Trough and Suruga trough. Interplate coupling is moderate to strong at 10-25 km depth along the Nankai Trough, but it is lower at ~132°E, ~136°E, and ~137°E than in the surrounding regions, corresponding to the segment boundaries of past megathrust earthquakes, suggesting that regions of insufficient strain accumulation act as a barrier for earthquake rupture.

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Section: Resultsmentioning

confidence: 95%

Strain partitioning and interplate coupling along the northern margin of the Philippine Sea plate, estimated from Global Navigation Satellite System and Global Positioning System-Acoustic data

et al. 2018

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“…Oceanfloor observations in the Tonankai region also could not detect earthquakes on the PHS interface ( Fig. 7 of Nakano et al 2015). However, on April 1, 2016, a shallow moderate earthquake suddenly occurred at the southeast offshore Mie prefecture, Kii Peninsula, Japan.…”

Section: Introductionmentioning

confidence: 94%

Moment tensor inversion of the 2016 southeast offshore Mie earthquake in the Tonankai region using a three-dimensional velocity structure model: effects of the accretionary prism and subducting oceanic plate

Takemura

Kimura

Saito

et al. 2018

Earth Planets Space

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The southeast offshore Mie earthquake occurred on April 1, 2016 near the rupture area of the 1944 Tonankai earthquake, where seismicity around the interface of the Philippine Sea plate had been very low until this earthquake. Since this earthquake occurred outside of seismic arrays, the focal mechanism and depth were not precisely constrained using a one-dimensional velocity model, as in a conventional approach. We conducted a moment tensor inversion of this earthquake by using a three-dimensional velocity structure model. Before the analysis of observed data, we investigated the effects of offshore heterogeneous structures such as the seawater, accretionary prism, and subducting oceanic plate by using synthetic seismograms in a full three-dimensional model and simpler models. The accretionary prism and subducting oceanic plate play important roles in the moment tensor inversion for offshore earthquakes in the subduction zone. Particularly, the accretionary prism, which controls the excitation and propagation of long-period surface waves around the offshore region, provides better estimations of the centroid depths and focal mechanisms of earthquakes around the Nankai subduction zone. The result of moment tensor inversion for the 2016 southeast offshore Mie earthquake revealed low-angle thrust faulting with a moment magnitude of 5.6. According to geophysical surveys in the Nankai Trough, our results suggest that the rupture of this earthquake occurred on the interface of the Philippine Sea plate, rather than on a mega-splay fault. Detailed comparisons of first-motion polarizations provided additional constraints of the rupture that occurred on the interface of the Philippine Sea plate.

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“…1 and Additional file 1: Figure S1) has facilitated continuous monitoring of offshore seismic activities Kawaguchi et al 2015). These observations revealed that, in recent years, earthquake activities along the Nankai Trough have mostly occurred in the oceanic crust or upper mantle of the subducting PSP (Obana et al 2004Obana and Kodaira 2009;Mochizuki et al 2010;Akuhara et al 2013;Nakano et al 2013Nakano et al , 2014Nakano et al , 2015Akuhara and Mochizuki 2014). The most recent notable events during this time have been the 2004 M JMA 7.1, 7.4, and 6.5 earthquakes off the Kii Peninsula, which occurred in the subducting plate (e.g., Sakai et al 2005;Seno 2005).…”

Section: Introductionmentioning

confidence: 95%

“…The simulation implies that the M6-class off-Mie earthquake was caused by shrinkage of the strongly coupled area along the plate boundary. Present seismic activities in the eastern Nankai Trough are mostly within the subducting or overriding plates, and there is very low activity in the rupture area of the megathrust earthquakes (Obana et al 2004;Obana and Kodaira 2009;Nakano et al 2015). However, Akuhara and Mochizuki (2014) observed continuous activity of an earthquake cluster with magnitudes smaller than 4 along the plate boundary west of the Kii Peninsula (labeled "A" in Fig.…”

Section: Earthquake Cycle Simulation Based On the Hierarchical Asperimentioning

confidence: 99%

The 2016 Mw 5.9 earthquake off the southeastern coast of Mie Prefecture as an indicator of preparatory processes of the next Nankai Trough megathrust earthquake

Hyodo

Nakanishi

Yamashita

et al. 2018

Prog Earth Planet Sci

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Megathrust earthquakes have occurred repeatedly at intervals of 100 to 150 years along the Nankai Trough, situated in the southwest of Japan. Given that it has been 70 years since the last event, the occurrence of the next devastating earthquake is anticipated in the near future. On April 1, 2016, a moderate earthquake (M w 5.9, M JMA 6.5) occurred off the southeastern coast of Mie Prefecture in the source region of the 1944 Tonankai earthquake (M w 8.2). In this study, we investigated the influence of the 2016 earthquake on future megathrust earthquakes. We first determined the hypocenter distributions using a precise velocity structure obtained from seismic surveys in the source region. Using data obtained from the DONET ocean-bottom observation network, we found that this earthquake occurred along the plate boundary fault, which is also believed to have slipped during past megathrust earthquakes. We then performed a preliminary numerical simulation to reproduce the occurrence of a moderate earthquake in the middle of a megathrust earthquake cycle. We used a hierarchical asperity model, in which smaller asperities causing moderate earthquakes are embedded in a hyper-asperity that serves as the source region of megathrust earthquakes. The simulation shows that moderate earthquakes, caused by ruptures of a smaller asperity, occur as a result of shrinkage of strongly coupled areas in the hyper-asperity. This result is consistent with the observation that the hypocenter of the 2016 earthquake was located at the edge of a strongly coupled region along the plate boundary. The simulation also reproduced postseismic slip (afterslip/slow slip) along the plate boundary updip of the hyper-asperity, which is consistent with the observations of slow slip events and very-low-frequency earthquakes after the 2016 earthquake. Thus, the occurrence of the moderate earthquake offshore southeastern Mie Prefecture in the middle of the megathrust earthquake cycle implies that the shrinkage of the strongly coupled area along the plate boundary is occurring as a preparatory process for the next megathrust earthquake in the region.

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Hypocenters in the Nankai Trough Determined by Using Data from Both Ocean‐Bottom and Land Seismic Networks and a 3D Velocity Structure Model: Implications for Seismotectonic Activity

Cited by 19 publications

References 43 publications

Strain partitioning and interplate coupling along the northern margin of the Philippine Sea plate, estimated from Global Navigation Satellite System and Global Positioning System-Acoustic data

Strain partitioning and interplate coupling along the northern margin of the Philippine Sea plate, estimated from Global Navigation Satellite System and Global Positioning System-Acoustic data

Moment tensor inversion of the 2016 southeast offshore Mie earthquake in the Tonankai region using a three-dimensional velocity structure model: effects of the accretionary prism and subducting oceanic plate

The 2016 Mw 5.9 earthquake off the southeastern coast of Mie Prefecture as an indicator of preparatory processes of the next Nankai Trough megathrust earthquake

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