The Nankai Trough is a vigorous subduction zone where large earthquakes have been recorded since the seventh century, with recurrence time of 100 to 200 years. 1946 Nankaido earthquake was unusual, rupture estimated from long-period geodetic data that more than twice as derived shorter period seismic data. In center this zone, we used densely deployed ocean bottom seismographs detect subducted seamount 13 kilometers thick by 50 wide at depth 10 kilometers. We propose might work barrier...

At the Japan Trench convergent margin, many large interplate earthquakes of greater than M7.5 frequently occur. Their epicenters have uneven distribution, mostly located in northern area. To investigate relationship between this distribution and tectonic structures, we conducted multichannel seismic surveys since 1996. Our data show two kinds sedimentary units: a wedge‐shaped unit channel‐like unit. Both units lower P wave velocity basal part overriding island arc crust. The having 2–3 km/s...

This paper describes a new testing method to examine the mechanical behavior of railroad ballast subjected repeated train passages on ballasted track. Two types cyclic loading tests, namely single-point test and moving-wheel test, were performed with small-scale models Next, “multi-ring shear apparatus” was developed as type torsional simple apparatus, applicability newly proposed multi-ring an element loads examined by comparing results tests those model tests. As result, it recognized that...

Abstract Hydration of the subducting oceanic plate determines amount water transported from Earth’s surface into its interior, and bending-related faulting (bend faulting) just prior to subduction is considered promote hydration. Bend shows significant spatial variation, but contribution hydration still poorly understood. Here we present results controlled-source seismic surveys around junction Japan Kuril trenches. We found structural changes caused by bend before differed distinctly...

Abstract Back‐arc basins are a primary target to understand lithospheric evolution in extension associated with plate subduction. Most of the currently active back‐arc formed intraoceanic settings and host well‐developed spreading centers where seafloor has occurred. However, rift structure at its initial stage, key how continental lithosphere starts break magma‐rich setting, is poorly documented. Here we present seismological evidence for southern Okinawa Trough, an zone behind Ryukyu...

Differences in the coseismic rupture process between 1944 Tonankai and 1946 Nankaido earthquakes have been studied by many fault models. To understand what factors control zones, it is important to investigate differences deep crustal structures of zones earthquakes. The previously published structure zone earthquake shows that extends Neogene‐Quaternary accretionary prism. However, little known about earthquake. obtain a complete image seismogenic earthquake, wide‐angle seismic survey was...

The Nankai Trough is a vigorous subduction zone where large earthquakes have been recorded with recurrence time of 100–200 yr. 1946 Nankaido earthquake well known as an unusual event among these earthquakes, because the rupture estimated from long-period geodetic data more than twice that derived seismic wave data. In summer 1999, onshore–offshore deep survey was performed along 355 km long profile in western seismogenic zone. Seismic signals both airgun array (207 1) and land explosions...

Research Article| November 01, 2007 New seismological constraints on growth of continental crust in the Izu-Bonin intra-oceanic arc Shuichi Kodaira; Kodaira 1Institute for Earth Evolution, Japan Agency Marine-Earth Science and Technology, Showa-machi 3173-25, Kanazawa-ku, Yokohama, Search other works by this author on: GSW Google Scholar Takeshi Sato; Sato Narumi Takahashi; Takahashi Seiichi Miura; Miura Yoshihiko Tamura; Tamura 2Institute Natsushima 2-15, Yokosuka, Yoshiyuki Tatsumi;...

A giant earthquake occasionally occurs in a subduction zone owing to simultaneous rupture adjacent segments which have been previously ruptured by large earthquakes. However, it is still unknown if coincidentally occurs, or there causal factor control its generation. In this study we show cause and growth process of may occur along southwestern Japan, on the basis seismic images obtained from wide‐angle data numerical simulation incorporating structural images. The were acquired three trough...

Abstract The nature of incoming sediments is a key controlling factor for the occurrence megathrust earthquakes in subduction zones. In 2011 Mw 9 Tohoku earthquake (offshore Japan), smectite-rich clay minerals transported by subducting oceanic plate played critical role development giant interplate coseismic slip near trench. Recently, we conducted intensive controlled-source seismic surveys at northwestern part Pacific to investigate plate. Our reflection data reveal that thickness sediment...

We present the results of structural and stratigraphic interpretations for multichannel seismic profiles to reveal structure Nankai accretionary wedge off Shikoku Island. On basis reflection characteristics we identify three major units that correspond a unit consisting both Oligocene‐Miocene prism sedimentary cover (unit A), underthrust Miocene‐Pliocene hemipelagic sediments B), subducting pre‐Miocene oceanic crustal rocks C). According relative strength topmost reflector B can be divided...

We present the results of an onshore–offshore wide‐angle refraction and reflection experiment off Miyagi, in central Japan Trench forearc region. There are two rupture zones large interplate earthquakes here: landward zone trenchward zone. To examine influence plate boundary geometry on distributions zones, we determined reflector geometries from reflections. The subducting oceanic increases its dip about 5° to 13° around 143.2°E. This bending point corresponds eastern edge Moreover, another...

To investigate megathrust earthquake and tsunami generation in a subduction seismogenic zone, it is important to know the detailed structure around plate boundary active splay‐fault system. The Nankai Trough, southwestern Japan, among best studied zones with splay faults world. This paper presents structural image fault coseismic rupture zone of 1944 Tonankai central based on results from wide‐angle, high‐density ocean bottom seismograph (OBS) survey. Our seismic clearly shows for first time...

We carried out a reflection/refraction seismic survey across the southern Izu‐Ogasawara arc–back arc system, covering three arcs with different crustal ages. The oldest Eocene has middle and lower crust high velocities of 6.4–6.6 6.8–7.4 km/s, respectively, suggesting denser materials. current volcanic 5.7–6.5 6.7–7.1 advanced differentiation. crust‐mantle transition layer, velocity 7.5–8.0 is distributed beneath rear arc, pool dense materials emanating from through growth. These structural...

Abstract Newly obtained high‐resolution seismic data reveal the detailed structure of Japan Trench axis off Miyagi, Japan, in region large shallow slip during 11 March 2011 M9 Tohoku earthquake. Correlation images with previous drilling results identifies a possible basal chert‐rich layer and hemipelagic/pelagic mudstones overlying igneous Pacific crust. Mapping acoustic basement depicts subduction horst‐and‐graben topography. The chert are subducted beneath seismically chaotic frontal...

Abstract It has been recognized that even weakly coupled subduction zones may cause large interplate earthquakes leading to destructive tsunamis. The Ryukyu Trench is one of the best fields study this phenomenon, since various slow and tsunamis have occurred; yet fault structure seismic activity there are poorly constrained. Here we present seismological evidence from marine observation for megathrust faults low-frequency (LFEs). On basis passive find LFEs occur at 15–18 km depths along...