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). 124. 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 … Honshu itself is formed from the island arc developed over the subducting plate. 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 … [2], The megathrust dip increases from about 5° near the surface to 10° as it passes beneath the coast of Honshu. Collett, T. S., 2002, Energy resources potential of natural gas hydrates, AAPG Bulletin, v. 86, pp. Furthermore, Pisani et al., 2006, identified protothrusts and decollement surfaces along the Nankai Trough. Interested in earthquakes, particularly in Asia Pacific and South Asia region, the Nankai Trough, subduction zone related events, tsunami earthquake, intraplate earthquakes. 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). 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. Steurer, J., Underwood, M, 2003, Clay mineralogy of mudstone from the Nankai Trough reference sites 1173 and 1177 and frontal accretionary prism site 1174, Ms 190SR-211. On all but one occasion, rupture of segment C (±D ±E) has been followed by rupture of segments A+B within a few years. The Nankai Trough is the near-surface extension of a zone of active seismicity that dips beneath SW Japan. Other interesting results of the pressure measurements were the pressure changes that resulted from sediment deformation near boreholes and the effect of very low earthquake swarms at the time of pressure changes (Davis et al., 2006). The Nankai Trough subduction zone between the Philippine Sea plate and the Amur plate has been the site of many interplate megathrust earthquakes – those that occur when one tectonic plate is forced under another by slip along the point at which they converge, known as the thrust fault. 252–264. In one recorded case (the 1707 Hōei earthquake) the fault ruptured along its entire length. The Nankai Trough is the near-surface extension of a zone of active seismicity that dips beneath SW Japan. This plate boundary would be an oceanic trench except for a high flux of sediments that fills the trench. It would cost as much as 40 per cent of Japan’s gross … Furthermore, seismic reflection studies have revealed the presence of basement highs that are interpreted as seamounts that are covered in sediments (Ike, 2004). Recently there has been an increase in interest in the release of water from illite clays in subducting sediments. Several thrust faults were identified by Operto et al., 2006, of which the thrust faults closest to the subduction zone are active. Deformation is concentrated in the outermost imbricate zone, with a significant amount of "out of sequence" thrusting occurring landward. It occurred on December 21, 1946, at 04:19 JST (December 20, 19:19 UTC). Furthermore, the short period seismicity appears to have some degree of dependency on bathymetric highs such as seamounts. Despite the uncertainty of when such an earthquake will occur, local authorities are already taking action to prepare … 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. The upper portion of the upper accretionary prism and the underlying backstop are currently undergoing a great deal of compressional pressure. Some sources use the Julian calendar for the earlier earthquakes in the list. Spinelli, G., Mozley, P., Tobin, H., Hoffman, N., Bellew, G., 2007, Diagenesisi, sediment strength, and pore collapse in sediment approaching the Nankai Trough subduction zone, GSA Bulletin, v. 119, pp. 73–84. Furthermore, there is a geothermal alteration of the smectite, converting it to illite clay (Steurer et al., 2003). 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. 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. This page was last edited on 28 October 2020, at 05:11. Conventional geologic estimates of plate movement velocities are difficult in the Nankai Trough because there are no spreading ridges that bound the tectonic plate. Nankai Trough earthquake risk map. 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. Gas hydrates nearest the trough appear to be sourced mainly from dewatering associated with subduction, while with increasing distance from the trough the sourcing is more a result of lateral movement of methane enriched waters (Muramatsu et al., 2006). 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). 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. Historically, the most recent large-scale earthquake to occur in the Nankai Trough was in 1944 off the Kii Peninsula. 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. 391–404. 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. 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]. [3] As basin formation stopped and sedimentation took place, the sediments acted like a blanket to trap the heat below. This area was not in the original NUVEL models (DeMets et al., 1990). 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. 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… 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. However, using the Eurasia to North America plate motion, the estimated rate was 2–4 mm/yr (DeMets et al., 1990). 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. Reaching temperatures of approximately 130 °C in other areas would require collecting cores from approximately 4 kilometers below the seafloor, rather than 1.2 kilometers as planned by Expedition 370. Katsushisa, K., Masayuki, T., 2004, Short-period seismic radiation zones of a megathrust fault along the Nankai, Trough deduced from inversion analysis of seismic intensity data, Journal of Seismilogical Society of Japan, v. 57, no. 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. 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