Strike-slip motion of a mega-splay fault system in the Nankai oblique subduction zone

Tsuji, Takeshi; Ashi, Juichiro; Ikeda, Yasutaka

doi:10.1186/1880-5981-66-120

Cited by 47 publications

(50 citation statements)

References 58 publications

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“…If time-dependent failure of borehole wall due to drilling-induced overconsolidation of porous sediments ) occurred, the magnitudes of horizontal stress that also favor thrust faulting would be even higher. These may agree with the strike-slip and thrusting motion of the megasplay fault suggested by the geometric features around the fault on seismic profiles and ocean floor topography (Tsuji et al 2014).…”

Section: Stress Orientationssupporting

confidence: 77%

Small-scale stress fluctuations in borehole breakouts and their implication in identifying potential active faults around the seismogenic megasplay fault, Nankai Trough, SW Japan

Yamada

Shibanuma

2015

Earth Planet Space

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Borehole breakouts are enlargements and elongation of a borehole in a particular direction, caused by failure of the borehole wall rock due to concentration of stresses around the borehole, and thus, have been widely used to determine the in situ stress orientation. We used electrical borehole wall images obtained during offshore scientific drilling (IODP) that penetrated through a seismogenic megasplay fault in the Nankai Trough, off SW Japan, and extracted a number of borehole breakouts. Most of the breakouts show directions that can be explained by the regional convergence, but some are obviously rotated by faults and fractures in the megasplay fault zone and in its hanging wall. Stress magnitudes estimated from the width of the breakouts also show some decrease in the horizontal stresses, suggesting that slip along the faults and fractures release shear stress affecting these surfaces. Since such surfaces may have the capability to reactivate where the stresses affecting the surface are geometrically appropriate, the method presented in this paper may contribute to identifying active fault surfaces. This knowledge allows us to identify which surfaces need to be examined in detail to assess their potential for future activity.

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Section: Stress Orientationssupporting

confidence: 77%

Small-scale stress fluctuations in borehole breakouts and their implication in identifying potential active faults around the seismogenic megasplay fault, Nankai Trough, SW Japan

Yamada

Shibanuma

2015

Earth Planet Space

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“…A real fault system consists of deep mega-splay fault (detachment fault) and seaward decollement; both are plateparallel, and the mega-splay fault that is branching to the surface and having a dip angle is considerably larger than assumed here (e.g., Tsuji et al 2014). Ruptures at subsources on the mega-splay fault would result in large GF amplitudes due to intensive generation of surface waves.…”

Section: Discussionmentioning

confidence: 99%

Visualization of Green’s function anomalies for megathrust source in Nankai Trough by reciprocity method

Petukhin¹,

Miyakoshi²,

Tsurugi³

et al. 2016

Earth Planet Sp

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We used simulation by the reciprocity method to visualize the distribution of Green's function amplitudes in the source of a megathrust earthquake in the Nankai Trough and considered the effects of various areas (asperities or strong motion generation areas) on the simulated long-period ground motions at Konohana in the Osaka basin. We employed a fault source model proposed for an anticipated M9-class event in the Nankai Trough and the 3D Japan Intergrated Velocity Structure Model developed for simulations of long-period ground motions in Japan. Green's functions were calculated for about 1400 subsources by combining the finite-difference method and the reciprocity approach. Depths, strikes, and dips of subsources were adjusted to the shape of the upper boundary of the Philippine Sea plate. Ground motions with periods of 4-20 s were considered. The simulated distribution of peak amplitudes of Green's functions identified two strongly anomalous areas: (1) a large along-strike elongated area just south of the Kii Peninsula and (2) a parallel area closer to the trench. The elongation of the anomalies corresponded well with depth isolines at the top of the Philippine Sea plate. Postulating that plate shape influences simulated ground motions, we investigated the effect on Green's function amplitudes of phenomena related to plate shape: radiation pattern; variations of medium properties (e.g., velocity and density) at subsource depths; depth, strike, and dip; and the effect of soft sediments. We suggest that the cumulative effect on Green's function amplitudes of subsource radiation patterns, medium properties at subsource depth, reflection from crustal interfaces, and passage through soft sedimentary layers plays a critical role in the formation of amplitude anomalies. Analysis of waveforms and the time delay of peak amplitude demonstrate that large-amplitude waves of Green's functions in shallow parts of the plate boundary are composed mostly of surface waves.

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“…In terms of fault type, almost all of those faults may have been originally formed as normal faults because their dips range from 30 to 60 degrees, which are consistent with the typical dip angles of normal faults. Namely, those faults would have been reactivated after the oblique subduction (e.g., Seno et al 1993) as strike-slip faults (Tsuji et al 2014). …”

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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Strike-slip motion of a mega-splay fault system in the Nankai oblique subduction zone

Cited by 47 publications

References 58 publications

Small-scale stress fluctuations in borehole breakouts and their implication in identifying potential active faults around the seismogenic megasplay fault, Nankai Trough, SW Japan

Small-scale stress fluctuations in borehole breakouts and their implication in identifying potential active faults around the seismogenic megasplay fault, Nankai Trough, SW Japan

Visualization of Green’s function anomalies for megathrust source in Nankai Trough by reciprocity method

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

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