The September 5, 2004 off the Kii Peninsula earthquakes as a composition of bending and collision

Seno, Tetsuzo

doi:10.1186/bf03352571

Cited by 12 publications

(15 citation statements)

References 29 publications

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“…Taking into consideration these observations, the stress field in the PHS plate in our study area is clearly anomalous. One possible explanation is that the stress field has been disturbed by collision at the Izu Peninsula east of our study area (e.g., Obana et al 2004;Seno 2005;Miyoshi and Ishibashi 2005), but the large difference in orientation of the axes of compressional stress are not well explained by this model. This question requires further investigation.…”

Section: Discussionmentioning

confidence: 75%

“…Accordingly, we would have expected a similar stress field in the PHS plate below southeast of the Kii peninsula, too. Bending of the plate due to subduction may also affect the stress field within the PHS plate (e.g., Seno 2005;Miyoshi and Ishibashi, 2005), in which compressional and tensional stress perpendicular to the trough axis dominate in the lower and upper parts, respectively, within the lithosphere. However, these mechanisms could not explain the observed direction of compressive stress oriented perpendicular to the direction of plate convergence.…”

Section: Discussionmentioning

confidence: 99%

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Seismic activity beneath the Nankai trough revealed by DONET ocean-bottom observations

2013

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We conducted a detailed investigation of seismic activity from January 2011 to February 2013 along the Nankai trough off the Kii Peninsula, central Japan, by using data obtained from the DONET ocean-bottom observation network. The hypocenters are mostly within the subducting Philippine Sea (PHS) plate, although a few are along the plate boundary or in the sedimentary wedge below the Kumano forearc basin. The seismic activity can be separated into events above and below 20 km depth, which corresponds approximately to the Moho. The hypocenter distributions are distinctly different for these groups. The seismic activity in the oceanic crust can be further separated into three clusters. Most of the seismic activity recorded in our data represents aftershocks of the 2004 off the Kii Peninsula earthquakes (M JMA = 7.1, 7.4, and 6.5), which occurred in the PHS plate. The hypocenter distribution in the oceanic crust correlates well with the location of the Paleo-Zenisu ridge, which is formed by a chain of seamounts that is subducting beneath the forearc basin. The hypocenters in the uppermost mantle are aligned on a plane dipping to the southeast, consistent with the existence of a thrust fault cutting through the lithosphere of the oceanic plate. The focal mechanisms of the earthquakes show that the axis of compressive stress in the PHS plate is oriented N-S, almost perpendicular to the direction of plate convergence, indicating a complex tectonic regime in this region. These results suggest that intraplate shortening may be occurring in the subducting oceanic plate.

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Section: Discussionmentioning

confidence: 75%

Section: Discussionmentioning

confidence: 99%

Seismic activity beneath the Nankai trough revealed by DONET ocean-bottom observations

2013

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“…9(a). Microearthquake activity is low in the rupture area of the Tonankai earthquake, whereas it is higher in trench-outer rise region (Seno, 2005;Sakai et al, 2005, see the top of Fig. 9(a)).…”

Section: Discussionmentioning

confidence: 98%

An improved double-difference earthquake location algorithm using s P phases: application to the foreshock and aftershock sequences of the 2004 earthquake offshore of the Kii peninsula, Japan (Mw=7.5)

et al. 2006

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We have used s P phases to improve the hypocentral locations of the earthquakes that occurred offshore southeast of the Kii peninsula in association with the M w =7.5 mainshock on September 5, 2004. The earthquakes were more than 100 km from the onshore seismic network and, thus, their focal depths were poorly constrained. The s P phases were recorded about 7-11 s after the initial P phases, with both phases having almost the same apparent velocities. The computation of ray-paths revealed that the arrival times of the later s P phases are sensitive to focal depths. We have recalculated the hypocenters and origin times for 36 events with more than six s P phase identifications on seismograms recorded at the High Sensitivity Seismograph Network by including s P phases in a double-difference earthquake location algorithm, which eliminates the errors introduced by crustal heterogeneity. The relocation results were then compared with those from the Japan Meteorological Agency based on traditional absolute location techniques. Key words: The 2004 earthquake offshore of the Kii peninsula, foreshock and aftershock sequences, improved double-difference earthquake location algorithm using s P phases, Philippine Sea plate.

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“…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: 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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The September 5, 2004 off the Kii Peninsula earthquakes as a composition of bending and collision

Cited by 12 publications

References 29 publications

Seismic activity beneath the Nankai trough revealed by DONET ocean-bottom observations

Seismic activity beneath the Nankai trough revealed by DONET ocean-bottom observations

An improved double-difference earthquake location algorithm using s P phases: application to the foreshock and aftershock sequences of the 2004 earthquake offshore of the Kii peninsula, Japan (Mw=7.5)

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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