Deep crustal structure of the eastern Nankai Trough and Zenisu Ridge by dense airgun–OBS seismic profiling

Nakanishi, Ayako; Shiobara, Hajime; Hino, Ryota; Mochizuki, Kimihiro; Sato, Toshinori; Kasahara, Junzo; Takahashi, Narumi; Suyehiro, Kiyoshi; Tokuyama, Hidekazu; Segawa, Jiro; Shinohara, Masanao; Shimahura, Hideki

doi:10.1016/s0025-3227(02)00244-x

Cited by 29 publications

(24 citation statements)

References 21 publications

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“…7a, b, the thrust below the Nankai trough assumed in this study dips southeast (Fig. 7a), whereas the thrust below the Zenisu ridge of previous studies (e.g., Nakanishi et al 1998Nakanishi et al , 2002bMazzotti et al 2002) dips northwest. In mechanical terms, these thrusts are not contradictory; both reflect compressive stress within the PHS plate.…”

Section: Discussionmentioning

confidence: 46%

“…1). Below this bathymetric high a thrust is found in the lithosphere of the PHS plate (e.g., Lallemant et al 1989;Nakanishi et al 1998Nakanishi et al , 2002bMazzotti et al 2002). Northwest of this ridge, the Paleo-Zenisu ridge is a similar bathymetric high formed on the PHS plate, which is also subducting beneath the Kumano forearc basin (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…1). The ridge runs almost parallel to the trough axis and a thrust cutting through the lithosphere of the PHS plate is found below this ridge (e.g., Lallemant et al 1989;Nakanishi et al 1998Nakanishi et al , 2002bMazzotti et al 2002). The slip on the thrust below this ridge may indicate shortening of the oceanic plate in this region (e.g., Mazzotti et al 2002).…”

Section: Introductionmentioning

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: 46%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

2013

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“…Trial depths were tested for a range of values from 0 to 25 km shallower than the JMA depth, which correspond to actual trial depths of about 5 to 50 km. While the earthquakes occurred in a rather complex 3D structure, we consider a 1D velocity model to be sufficient since the subducting slab in this region of the Nankai Trough, where the Kii Peninsula events have occurred, dips at a shallow angle (see Nakanishi et al, 2002). The velocity model (Table 1 in Fig.…”

Section: Data and Methods Of Analysismentioning

confidence: 99%

Double-difference relocations of the 2004 off the Kii peninsula earthquakes

2005

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Two large earthquakes (Mw7.3 and Mw7.5) occurred off-shore of the Kii peninsula (Japan) on 5th September 2004. The insufficient station coverage in the area where the large events and their aftershocks occurred led to significant uncertainty regarding their depth location. By using a double-difference approach, we were able to determine more accurate hypocenter locations and better define the main characteristics of the aftershock distribution. The data we used in this study comprise of about 700 earthquakes recorded by the Japanese Meteorological Agency (JMA) from 5 to 12 September 2004. We assume several depth ranges for the initial double difference earthquake locations and select the solution with the smallest rms residual. The resulting hypocenter distribution has two distinctive features: 1) on average the depths are about 20 km shallower than the initial JMA location and 2) the hypocenters are divided into two groups: one shallow (around 12 km depth) and another deep (around 27 km depth). The epicenters of the relocated events define a finer, more clustered structure compared with the epicentral distribution of JMA. The splitting of the earthquake locations into two depth groups is still observed when using a significantly different velocity structure. Our results of the two depth groups for the hypocenters resemble the independently determined hypocentral distribution from the OBS survey.

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“…1). The normal oceanic crust was identified beneath the Zenisu Ridge by a velocity structure study using OBS (Nakanishi et al 2002), and the magnetization highs associated with the ridge topography were identified by a magnetic inversion study (Kido and Fujiwara 2004). Thus, if volcanic activity associated with the ridge formation (e.g., Bandy and Hilde 1983) overprinted normal oceanic crust, more porous volcanic rocks should be contained in the overprinted crust than in the normal one.…”

Section: Type and Present Activity Of Faultsmentioning

confidence: 99%

Visualization of attenuation structure and faults in incoming oceanic crust of the Nankai Trough using seismic attenuation profiling

Tsuru

Park

et al. 2018

Earth Planets Space

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Seismic attenuation properties were tested as indicators of lateral variation in geological structures and detection of faults within poorly reflective oceanic crust, on a seismic survey line along the Nankai Trough. We can specify both sedimentary structures by configuration of reflections and faults by offsetting of reflections on seismic reflection profiles. This procedure is often applied to analyze geological structures and existence of faults within sedimentary layers; however, it is almost impossible to analyze them within igneous oceanic crust because seismic reflections are inherently invisible there. Therefore, we applied seismic attenuation profiling to visualize geological structures and faults within poorly reflective oceanic crust. As a result, oceanic crust altered by late-coming volcanisms as well as damaged by intraplate earthquakes was imaged as extremely high-attenuation property, which was clearly distinguished from normal oceanic crust. Many faults were observed in the sedimentary unit on the seismic reflection profile, whereas possible lower segments of the faults were imaged as high-attenuation stripes in the oceanic crust on the seismic attenuation profile. Thus, the effectiveness of seismic attenuation profiling to structural and fault imaging within poorly reflective oceanic crust was successfully demonstrated.

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Deep crustal structure of the eastern Nankai Trough and Zenisu Ridge by dense airgun–OBS seismic profiling

Cited by 29 publications

References 21 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

Double-difference relocations of the 2004 off the Kii peninsula earthquakes

Visualization of attenuation structure and faults in incoming oceanic crust of the Nankai Trough using seismic attenuation profiling

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