All of these great earthquakes have resulted in damaging tsunamis, which are particularly damaging due to the Japanese population being concentrated on the Taiheiyō Belt, especially the coastal cities of Tokyo and Osaka, the two most populous in Japan. 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. 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). Conventional geologic estimates of plate movement velocities are difficult in the Nankai Trough because there are no spreading ridges that bound the tectonic plate. Mitsui, N., Hirahara, K., 2004, Simple spring-mass Model simulation of earthquake cycle along the Nankai Trough in Southwest Japan, Pure Applied Geophysics, v. 161, pp. These five subdivisions show interesting differences in earthquakebehavior: frequency of earthquakes varying on a 90 to 150-year cycle (Mitsui, et al., 2004; Tanioka et al., 2004), similar slip occurrences along the fault segments, the order of subdivision faulting, and finally, different failure feat… A government committee outlines the possibilities of coastal areas experiencing tsunami of different heights if a quake with a magnitude of 8 to 9 occurs in the Nankai Trough. Furthermore, the short period seismicity appears to have some degree of dependency on bathymetric highs such as seamounts. 245-10, 2005 Salt Lake City Annual Meeting. Zhao, S., Wu, X., Hori, T., Smith, A., Kaneda, A., Takemoto, S., 2003, Deformation and stress localization at the Nankai subduction zone, southwest Japan, Earth and Planetary Science Letters, v. 206, pp. The pattern of historical seismicity reveals that the megathrust surface is segmented, with five separate zones of rupturing identified, conventionally labelled A–E, from west to east. 809–819. Collett, T. S., 2002, Energy resources potential of natural gas hydrates, AAPG Bulletin, v. 86, pp. Despite the uncertainty of when such an earthquake will occur, local authorities are already taking action to prepare … 243302450. 2, pp 153–177. The earthquake repeat intervals are generally in the range 90–200 years. 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. Operto, S., Virieux, J., Dessa, J., Pascal, G., 2006, Crustal seismic imaging from multifold on bottom seismometer data by frequency domain full waveform tomography: Application to the eastern Nankai trough, Journal of Geophysical Research, v. 111, doi:1029/2005/B003835. Four phases and seven key tasks In this area, the main sedimentological controls for the accumulation of gas hydrates are the sand-rich areas of the trough (Collett, 2002). 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 offshore. 1015–1018. Interested in earthquakes, particularly in Asia Pacific and South Asia region, the Nankai Trough, subduction zone related events, tsunami earthquake, intraplate earthquakes. The underlying fault, the Nankai megathrust, is the source of the devastating Nankai megathrust earthquakes, while the trough itself is potentially a major source of hydrocarbon fuel, in the form of methane clathrate. 34–35. 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. Hydrologic observatories were placed in boreholes drilled in 2000 (IODP sites 808 and 1173) in an attempt to quantify changes in pore-fluid pressure that are a result of the oncoming Philippine Sea plate (Davis et al., 2006). This is the first in a series of investigative reports from the Chunichi Shimbun about how figures for the probability of a Nankai Trough earthquake were manipulated for a … [2], The megathrust dip increases from about 5° near the surface to 10° as it passes beneath the coast of Honshu. This is because the mathematics of this model only used twelve plates, and the Philippine Sea and Eurasian convergent margin were not included. [9] A death toll as high as 230,000 has been suggested for such an event.[10]. In order to minimize the damage from the Nankai Trough Earthquake, it is necessary to take countermeasures for liquefaction. 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). 11, pp. A study by the Japan Society of Civil Engineers in 2018 estimated that the long-term damage from the earthquake could result in 1,240 trillion yen in economic losses over a 20-year period. Kastner, 2001, Gas ydrates in convergent margins: formation, occurrence, geochemistry, and global significance. Matsushima, J., 2006, Seismic wave attenuation in methane hydrate-bearing sediments: Vertical seismic profiling data from the Nankai Trough exploratory well, offshore Tokai, central Japan. The Japanese government predicts that an earthquake of immeasurable scale will strike Japan along the Nankai-Trough within the next 30 years. The rupture zone has been subdivided into five areas with respect to seismic modelling (Mitsui et al., 2004). Rapid sedimentation resulted in a greater retention of heat. Saito, H., Suzki, N., 2007, Terrestria organic matter controlling gas hydrate formation in the Nankai Trough accretionary prism, offshore Shikoku, Japan, Journal of Geochemical Exploration, v. 95, pp. 1971–92. 73–84. Based on the work of Operto et al., 2006, several areas of intense tectonic activity in the Nankai Trough were identified using full waveform tomography. Obana, K., Kodaira, S., Kaneda, Y., 2006, Seismicity related to heterogeneous structure along the western Nankai trough off Shikoku Island, Geophysical Research Letters. Documented Nankai Trough earthquakes and related tsunamis date back to the 7th century CE and suggest that M8-class great earthquakes have occurred at an interval of 100–200 years in this region (HERP, 2013), with 75 years having passed since the … Typically porosity decreases with increasing depth. The Nankai trough runs roughly parallel to the Japan Median Tectonic Line. 67–86. Analysis of seismic reflection data suggests that some of the displacement is carried by a splay fault dipping at about 25°. Despite the uncertainty of when such an earthquake will occur, local authorities are already taking action to prepare residents for what they regard as an inevitability. [4] The area was originally a basin (Shikoku Basin) with active hydrothermal activity during its formation. The conversion of smectite to illite (illitization) in subduction zones is likely driven by the higher temperature found in the subduction zone as opposed to non-subducting sediments (Saffer et al., 2005). 377–390. The Nankai Trough is a very large ditch located in the seabed south of Shikoku. The working hypothesis is that pressure changes indicate a change in the elastic strain within the formation (Davis et al., 2006). Had an unforgettable moment with one back in 2012 . A biennial survey by Shizuoka Prefecture showed in 2017 that the percentage of residents “very interested” in the Nankai Trough or Tokai earthquakes stood … Historically, the most recent large-scale earthquake to occur in the Nankai Trough was in 1944 off the Kii Peninsula. [3] However, the trough is potentially a major source of hydrocarbon fuel, in the form of methane clathrate. American Geophysical Union Washington, DC, pp. Furthermore, Pisani et al., 2006, identified protothrusts and decollement surfaces along the Nankai Trough. REVEL-based calculations indicate that there is no accumulation of strain at the trench. 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. After the twenty-first century, the Global Navigation Satellite System-Acoustic ranging (GNSS-A) technique detected geodetic events such as co- and postseismic effects following the 2011 Tohoku-oki earthquake and slip-deficit rate distributions along the Nankai Trough subduction zone. 534–556. Saffer, D., Underwood, M., McKiernan, A., 2005, Smectitie transformation in the Nankai trough: Effects on subduction zone mechanics and hydrogeology, Paper, No. Furthermore, seismic reflection studies have revealed the presence of basement highs that are interpreted as seamounts that are covered in sediments (Ike, 2004). Nankai Trough earthquake risk map. It is so active that there are a lot of earthquakes. Krason, 1994, Study of 21 marine basins indicates wide prevalence of hydrates, Offshore, August, pp. The area remains seismically active, and future earthquakes are anticipated, with a high risk of a Nankai earthquake in the near future, which could be potentially very damaging. Colwell, F., Matsumoto, R., Reed, D., 2004, A Review of gas hydrate, geology and biology of the Nankai Trough, Chemical Geology, v. 205, pp. Obana, K., Kodaira, S., Keneda, Y., 2005, Seismicity in the incoming/subducting Philippine Sea plate off the Kii Peninsula, central Nankai trough, Journal of Geophysical Research, v. 110. The northern part of the trough is known as the Suruga Trough, while to the east is the Sagami Trough. Overview of Nankai Trough Mega Earthquake Operation Plan To be ready for a national crisis should the Nankai Trough Mega Earthquake occur, we are making every effort to promote various operations. Nevertheless as of 2014[update] there is no commercial exploitation. 1980 ). This was determined by drilling a series of boreholes and measuring the concentration, as well as radiometric age determination of the halogen elements iodine, bromine, and chlorine (Tomaru et al., 2007). Drill cores from the seaward edge of the Nankai Trough (where the heat flow is one of the highest in the region) reveal that sediments there only reach pre-oil window to early oil window thermal maturities. The northeasternmost part of the megathrust, segment E, has not ruptured since 1854. [5] Earthquakes involving the A+B segments are generally referred to as Nankai (literally South Sea) earthquakes, C+D Tonankai (literally Southeast Sea) earthquakes and C+D+E Tokai (literally East Sea) earthquakes. 215–226. Baba, T., Cummins, P. R., 2005, Contiguous rupture area of two Nankai Trough earthquakes revealed by high resolution tsunami waveform inversion. It is predicted that the quake will cause a massive tsunami that could devastate the extensive coastline along the Pacific Ocean, from Shizuoka to Miyazaki (throughout central to west Japan). Recently there has been an increase in interest in the release of water from illite clays in subducting sediments. The rupture zone has been subdivided into five areas with respect to seismic modelling (Mitsui et al., 2004). There are indications of an increase in the retention of porosity within the rock. Pisani, P., Reshef, M., Moore, G., 2005, Targeted 3-D prestack depth imaging at Legs 190-196 ODP drill sites (Nankai Trough, Japan). Site 808 is located in the front section of the main thrust fault, while site 1173 is located approximately 11 km from the frontal thrust zone (Hitoshi et al., 2006). In one recorded case (the 1707 Hōei earthquake) the fault ruptured along its entire length. The Nankai accretionary complex is an area with high heat flow. It has been estimated that convergent margins may contain up to two-thirds of the total gas hydrate volume on the Earth (Kastner, 2001). Nankai Trough Earthquake Information Along the Nankai Trough, megathrust earthquakes with a magnitude 8 or more occur repeatedly. 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). However, there is an anomalous preservation of porosity at depth at drill site 1173. 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 … The presence of this 'weak' zone may lead to shallow coseismic rupture along the megasplay faults during megathrust earthquakes, explaining the large tsunamis created by these events.[4]. Of methane clathrate the last ca page was last edited on 28 October 2020, at 05:11 along entire..., S., 2002, Energy resources potential of natural gas hydrates ( Colwell et,... 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