Seismic imaging and velocity structure around the JFAST drill site in the Japan Trench: low Vp, high Vp/Vs in the transparent frontal prism

Nakamura, Yasuyuki; Kodaira, Shuichi; Cook, Becky; Jeppson, T.; Kasaya, Takafumi; Yamamoto, Yojiro; Hashimoto, Yoshitaka; Yamaguchi, Mika; Obana, Koichiro; Fujie, Gou

doi:10.1186/1880-5981-66-121

Cited by 37 publications

(27 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…1). The data were first processed following a conventional flow as described by Nakamura et al (2014). The processing flow included minimum phase conversion, predictive deconvolution, common midpoint sorting, velocity analysis, normal moveout, stacking, and poststack time migration.…”

Section: Data Acquisition and Processingmentioning

confidence: 99%

“…Details of the PSDM procedure were described in Nakamura et al (2014). We applied a layer-cake approach for the PSDM velocity analysis, in which we determined the velocity downward from the shallowest unit.…”

Section: Data Acquisition and Processingmentioning

confidence: 99%

“…Assuming that the frontal prism has been developed since the Eocene, based on the age of the oldest pelagic sediments sampled at the JFAST site (e.g., Rabino witz et al, 2015), we estimate that only ~2% of the input sediment contributes to form the frontal prism and the remaining ~98% of the input sediment has been subducted [i.e., an average of the volume of the frontal prism per 1 m along the trench is 4 × 10 7 m 3 (Table 1); a total input sediment volume since the Eocene per 1 m along the trench is 8 × 10 -2 m/yr (plate convergent rate) × 5 × 10 2 m (thickness of the sediment) × 5 × 10 7 yr (since Eocene) = 2 × 10 9 m 3 ]. To examine the along-trench variation of the frontal prism, we determined the volume and distribution of the frontal prism in six imaged sections, including the profile processed in Nakamura et al (2014) (Fig. 9), and compared them with data from Tsuru et al (2002), who processed 14 profiles in the Japan Trench subduction zone from 36°N to 41°N.…”

Section: Frontal Prismmentioning

confidence: 99%

See 2 more Smart Citations

Depth-varying structural characters in the rupture zone of the 2011 Tohoku-oki earthquake

et al. 2017

Self Cite

View full text Add to dashboard Cite

Seismic, geodetic, and tsunami data of the 2011 Tohoku-oki earthquake (offshore Japan; moment magnitude, M w 9.0) have revealed that large coseismic slip reached the trench axis. Moreover, a clear, depth-dependent variation in the source location between high-and low-frequency seismic energy radiation was observed. However, depth-varying structural features in the rupture zone have not been well examined. We therefore processed seismic reflection data acquired along five profiles in the rupture zone and examined depth-varying structural characteristics. In the resultant seismic images were interpreted a low-velocity frontal prism, a reflective zone at the trenchward tip of the continental block, and subducted horst and graben structures. The frontal prism, which was imaged as a low-velocity (Vp 2.0-3.5 km/s) wedgeshaped unit with seafloor widths of 13.5-18 km north of 37.5°N, changed abruptly to an elongate sedimentary unit south of 37.5°N. Landward of the frontal prism, 30-80 km from the trench axis, a reflective zone was imaged above the subducted oceanic basement. Subducted horst and graben structures were clearly imaged beneath the frontal prism and the reflective zone, and they could be found to a depth of 25 km. The throws of the normal faults delineating the horst and graben structures become larger landward to as much as 2 km. Comparison of the seismic images, earthquake seismicity, and slip behaviors showed that slips of tsunami earthquakes occur along the plate interface where the frontal prism is well developed. Background seismicity along the plate interface may extend downward to the landward end of the frontal prism and it becomes active around 25 km depth extending down the subduction zone.

show abstract

Section: Data Acquisition and Processingmentioning

confidence: 99%

Section: Data Acquisition and Processingmentioning

confidence: 99%

Section: Frontal Prismmentioning

confidence: 99%

See 1 more Smart Citation

Depth-varying structural characters in the rupture zone of the 2011 Tohoku-oki earthquake

et al. 2017

Self Cite

View full text Add to dashboard Cite

show abstract

“…Using constraints on age reversals and gaps, secondary faults have also been inferred at~790, 820,824,826,832,and 833 mbsf (Figure 1c) [Chester et al, 2013a;Rabinowitz et al, 2015]. Degree of lithification increases moderately with depth, indicated by increasing P wave velocity (m/s), rock density, and electrical resistivity (Ωm) measured in geophysical logs [Chester et al, 2013a;Nakamura et al, 2014]. Unconfined compressive strength of recovered rocks also increases with depth, ranging from 1 to 10 MPa [Chester et al, 2013a].…”

Section: Tectonic Settingmentioning

confidence: 99%

The damage is done: Low fault friction recorded in the damage zone of the shallow Japan Trench décollement

Keren

Kirkpatrick

2016

JGR Solid Earth

View full text Add to dashboard Cite

Fault damage zones record the integrated deformation caused by repeated slip on faults and reflect the conditions that control slip behavior. To investigate the Japan Trench décollement, we characterized the damage zone close to the fault from drill core recovered during Integrated Ocean Drilling Program Expedition 343 (Japan Trench Fast Drilling Project (JFAST)). Core‐scale and microscale structures include phyllosilicate bands, shear fractures, and joints. They are most abundant near the décollement and decrease in density sharply above and below the fault. Power law fits describing the change in structure density with distance from the fault result in decay exponents (n) of 1.57 in the footwall and 0.73 in the hanging wall. Microstructure decay exponents are 1.09 in the footwall and 0.50 in the hanging wall. Observed damage zone thickness is on the order of a few tens of meters. Core‐scale structures dip between ~10° and ~70° and are mutually crosscutting. Compared to similar offset faults, the décollement has large decay exponents and a relatively narrow damage zone. Motivated by independent constraints demonstrating that the plate boundary is weak, we tested if the observed damage zone characteristics could be consistent with low‐friction fault. Quasi‐static models of off‐fault stresses and deformation due to slip on a wavy, frictional fault under conditions similar to the JFAST site predict that low‐friction fault produces narrow damage zones with no preferred orientations of structures. These results are consistent with long‐term frictional weakness on the décollement at the JFAST site.

show abstract

“…Below the décolle-ment, rocks include middle to late Miocene brown siliceous mudstone, early Miocene stratified pelagic clay, and Late Cretaceous laminar chert at the total drilling depth (see the "Expedition 343/343T summary" chapter [Expedition 343/343T Scientists, 2013a]; Rabinowitz et al, 2015). Degree of lithification increases moderately with depth, indicated by increasing P-wave velocity (meters per second) and electrical resistivity (ohm-meters) (see the "Expedition 343/343T summary" chapter [Expedition 343/ 343T Scientists, 2013a]; Nakamura et al, 2014). Unconfined compressive strength of recovered rocks also increases with depth, ranging from 1 to 10 MPa (see the "Expedition 343/343T summary" chapter [Expedition 343/343T Scientists, 2013a]).…”

Section: Cores From Hole C0019e Used For Analysismentioning

confidence: 99%

Data report: tectonic and induced structures in the JFAST core

Keren¹,

Kirkpatrick²

2016

Proceedings of the IODP

View full text Add to dashboard Cite

Structures surrounding the inferred location of the Japan Trench plate boundary décollement define the fault damage zone. We quantify the density of tectonic and induced structures in the damage zone from drill cores collected between 770 and 835 meters below seafloor from Hole C0019E during Integrated Ocean Drilling Program Expedition 343/343T, the Japan Trench Fast Drilling Project (JFAST). Cores contain structures formed by tectonic deformation and structures resulting from drill core recovery and handling. Differentiating between these two origins is essential for structural analyses and interpretation. We defined 10 styles of induced structures that we used to develop a new set of criteria for identifying induced structures in drill cores containing fine-grained sedimentary rocks. These criteria were used to categorize structures according to confidence in a tectonic origin. Our results show structure density (including all fractures, faults, breccias, and phyllosilicate bands) has a maximum adjacent to the décollement. This pattern in structure density is apparent for both exclusively tectonic structures and tectonic and induced structures combined. Local increases in induced structure density mask trends in tectonic structures, demonstrating that detecting trends in spatial variability in structure density is dependent on the recognition of induced structures. Additionally, the tectonic structure density increases where cores contain faults with significant displacements inferred from stratigraphic information, indicating that tectonic structure density can be used to identify secondary faults. We suggest that the criteria for identifying induced structures used in this study could be applied during visual core description in a variety of tectonic settings as a method to collect and assess reliable structural data. IntroductionCoseismic thrust displacement during the 2011 Tohoku-Oki Mw 9.0 earthquake reached ~40-80 m near the trench, the largest slip ever recorded for an earthquake (Fujiwara et al., 2011;Fujii et al., 2011;Ide et al., 2011;Lay et al., 2011;Pollitz et al., 2011;Yue and Lay, 2011 T.T. Keren and J.D. KirkpatrickData report: tectonic and induced structures in the JFAST coreProc. IODP | Volume 343/343T 2 of the JFAST project included identifying and sampling the rocks that were deformed during the earthquake to establish the processes active on the fault during slip and to establish the stress state on the fault before, during, and after the earthquake (Mori et al., 2012). Structural data are critical for locating the plate boundary décollement, where both longterm and coseismic displacements are typically localized. The attitudes of fractures and faults around the fault also provide information about the stress field when they formed (see the "Expedition 343/343T summary" chapter [Expedition 343/343T Scientists, 2013a]).Drilling was undertaken at Site C0019, ~7 km landward of the trench in the region of maximum slip during the earthquake (Fig. F1) Distinguishing tectonic structures ...

show abstract

Seismic imaging and velocity structure around the JFAST drill site in the Japan Trench: low Vp, high Vp/Vs in the transparent frontal prism

Cited by 37 publications

References 26 publications

Depth-varying structural characters in the rupture zone of the 2011 Tohoku-oki earthquake

Depth-varying structural characters in the rupture zone of the 2011 Tohoku-oki earthquake

The damage is done: Low fault friction recorded in the damage zone of the shallow Japan Trench décollement

Data report: tectonic and induced structures in the JFAST core

Contact Info

Product

Resources

About