A future great earthquake involving rupture along this and possibly other segments has been proposed as a major risk for the southern coast of Honshu. On the other hand, M w 7-class earthquakes have repeatedly occurred in the Hyuga-nada Sea off Kyushu, southwest Japan, at a time interval of 10–20 years (e.g., Shiono et al. Tomaru, H., Lu, Z., Fehn, U., Muramatsu, Y., Matsumoto, R., 2007, Age variations of pore water iodine in the eastern Nankai Trough, Japan: Evidence for different methane sources in a large gas hydrate field, Geology, v. 35, no. Methane-rich horizons have been identified as areas of higher attenuation of sonic frequencies (10 to 20 kHz) and only slight attenuation of seismic frequencies (30 to 110 Hz) (Matsushima, 2006). In addition to informing earthquake disaster research, these findings also shed light on the marine sedimentary environment and plate tectonics of the Nankai Trough. The northeasternmost part of the megathrust, segment E, has not ruptured since 1854. This page was last edited on 28 October 2020, at 05:11. On all but one occasion, rupture of segment C (±D ±E) has been followed by rupture of segments A+B within a few years. [1] The megathrust boundary extends about 700 km from the southern end of Kyūshū to the triple junction with the Okhotsk Plate near Mount Fuji. A biennial survey by Shizuoka Prefecture showed in 2017 that the percentage of residents “very interested” in the Nankai Trough or Tokai earthquakes stood … In 1999, the likelihood of the occurrence of a great earthquake in the Tokai area in the period 2000-2010 was estimated to be in the range of 0.35–0.45. Seismically, the high bottom simulating reflectors are considered indicative of gas hydrates (Colwell et al., 2004). For this reason, the government will issue "Nankai Trough Earthquake Temporary Information (Giant Earthquake Alert)" when an earthquake of magnitude 8 or more occurs due to a displacement of about half of the epicenter area, and a mechanism to call attention … Nankai megathrust earthquakes are great megathrust earthquakes that occur along the Nankai megathrust – the fault under the Nankai Trough – which forms the plate interface between the subducting Philippine Sea Plate and the overriding Amurian Plate (part of the Eurasian Plate), which dips beneath southwestern Honshu, Japan. The rates of movement have been calculated to be in a range of 3.0 ± 1.8 mm/yr to 11.1 ± 1.7 mm/yr (Sella et al., 2002). A major earthquake is expected to strike sometime along the Nankai Trough, a submarine trench running off the Japanese archipelago from around Shizuoka Prefecture in … Zang, S., Chen, Q., Ning, J., Shen, Z., Liu, Y., 2002, Motion of the Philippine Sea plate consistent with NUVEL-1A model, Geophyiscal Journal International, v. 150, pp. It has been estimated that convergent margins may contain up to two-thirds of the total gas hydrate volume on the Earth (Kastner, 2001). The upper portion of the upper accretionary prism and the underlying backstop are currently undergoing a great deal of compressional pressure. 1980 ). Some sources use the Julian calendar for the earlier earthquakes in the list. The source of water for the formation of gas hydrates frequently comes from the dewatering of a subducting slab as well as the overriding plate (Muramatsu et al., 2006). [7] Interested in earthquakes, particularly in Asia Pacific and South Asia region, the Nankai Trough, subduction zone related events, tsunami earthquake, intraplate earthquakes. Krason, 1994, Study of 21 marine basins indicates wide prevalence of hydrates, Offshore, August, pp. The Nankai Trough (南海トラフ, Nankai Torafu, Southern Sea Trough) is a submarine trough located south of the Nankaidō region of Japan's island of Honshū, extending approximately 900 km (559 mi) offshore. [9] A death toll as high as 230,000 has been suggested for such an event.[10]. Furthermore, seismic reflection studies have revealed the presence of basement highs that are interpreted as seamounts that are covered in sediments (Ike, 2004). In plate tectonics, the Nankai Trough marks a subduction zone that is caused by subduction of the Philippine Sea Plate beneath Japan, part of the Eurasian plate (Kanda et al., 2004). Along the western area of the Nankai Trough, seismicity appears to be related to irregularities in crustal structure such as fractures generated from the subducted seafloor, including backarc basin crust of the Shikoku Basin, as well as due to serpentization of uppermost mantle beneath the overriding plate (Obana et al., 2006). The information concerning the gas hydrates in the Nankai Trough was initially published in 2000 by the Japan National Oil Corporations. Several thrust faults were identified by Operto et al., 2006, of which the thrust faults closest to the subduction zone are active. [1] Eventually, IODP Expedition 370 reached a temperature of ~120 °C at 1.2 kilometers below the seafloor[2][3] with mineral evidence showing that there are localized depths with significantly higher temperatures due to hot fluids.[3]. Within the Nankai Trough there is a large amount of deformed trench sediments (Ike, 2004), making one of Earth's best examples of accretionary prism. The rupture zone has been subdivided into five areas with respect to seismic modelling (Mitsui et al., 2004). Had an unforgettable moment with one back in 2012 . Hitoshi, M., Masonori, I., Tadanor, G., Takafu, K., 2006, Current research status and meaning of fluid pressure monitoring at the Nankai Trough, Journal of Geography, v. 115, n. 3, pp. [2], The megathrust dip increases from about 5° near the surface to 10° as it passes beneath the coast of Honshu. It is so active that there are a lot of earthquakes. In the Nankai Trough region, we were operating six seafloor sites along the trench axis at about 50 to 100 km intervals (Figure 1 and Table 1) before the 2011 Tohoku-oki earthquake. Demets, C., Gordon, R., ARgus, D., Stein, S., 1994, Effects of recent revisions to the geomagnetic reversal time scale on estimates of current plate motions, Geophysical Research Letters, v. 21, n. 20 pp. 245-10, 2005 Salt Lake City Annual Meeting. As mentioned previously, the NUVEL-1A plate motion model does not include the Philippine Sea plate. Conventional geologic estimates of plate movement velocities are difficult in the Nankai Trough because there are no spreading ridges that bound the tectonic plate. The Nankai Trough has been described as containing a large amount of gas hydrates and is one of the best studied sites of gas hydrate formations (Collett, 2002; Saito et al., 2007). About Nankai Trough Earthquakes The Nankai Trough is a deep ocean faultline whose northernmost point is Suruga Bay. IODP Expedition 370 will seek to find the temperature limit of the deepest life on Earth by drilling in the Nankai Trough, where heat flow is particularly high near its boundary with the subducting young, hot Philippine Sea tectonic plate. 2191–2194. The Nankai Trough is the near-surface extension of a zone of active seismicity that dips beneath SW Japan. The rupture zone has been subdivided into five areas with respect to seismic modelling (Mitsui et al., 2004). All the dates shown in the table use the Gregorian calendar. Ike, T., More, G., Okano, T., Kuramoto, S., Taira, A., Along strike changes in basement topography and sediment thickness in the northern Shikoku Basin: Variable inputs to the Nankai Trough Seismogenic Zone, EOS Transaction, American Geophyiscal Union, vol. However, using the Eurasia to North America plate motion, the estimated rate was 2–4 mm/yr (DeMets et al., 1990). For those earthquakes that affect the Nankai region specifically, see, "Tectonic evolution of the Japanese island arc system", "The age and origin of the Pacific islands: a geological overview", "Splay fault and megathrust earthquake slip in the Nankai Trough", "Broad, weak regions of the Nankai Megathrust and implications for shallow coseismic slip", "Simulation of Earthquake Generation Process in a Complex System of Faults", "Probability of a great earthquake to recur in the Tokai district, Japan", "A Disaster Prevention and Earthquake Experience Guide", "Study: Damage from Nankai quake could hit 1,240 trillion yen", "A Disaster to Dwarf 3/11? Plate-boundary earthquakes of magnitude 8 or greater along the Suruga–Nankai Trough subduction zone have repeated at intervals of 90–150 years, but with widely varying magnitudes and rupture areas. 243302450. 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