We propose, based on geologic data on crustal movements of the forearc wedge, that these earthquake variations are controlled by two separate locked zones in the deeper part of the plate … Seismically, the high bottom simulating reflectors are considered indicative of gas hydrates (Colwell et al., 2004). Furthermore, there is a geothermal alteration of the smectite, converting it to illite clay (Steurer et al., 2003). In one recorded case (the 1707 Hōei earthquake) the fault ruptured along its entire length. 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). 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. 34–35. 1015–1018. 11, pp. The Nankai trough runs roughly parallel to the Japan Median Tectonic Line. 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. The earthquake repeat intervals are generally in the range 90–200 years. Colwell, F., Matsumoto, R., Reed, D., 2004, A Review of gas hydrate, geology and biology of the Nankai Trough, Chemical Geology, v. 205, pp. Geophysical Monograph, vol. The Nankai Trough 南海トラフ (Nankai Torafu?) [2], The megathrust dip increases from about 5° near the surface to 10° as it passes beneath the coast of Honshu. The Nankai Trough Earthquake is expected to occur at a probability of 70% within the next 30 years (Kochi Prefecture, 2017). 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). 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. 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. The rupture zone has been subdivided into five areas with respect to seismic modelling (Mitsui et al., 2004). This was concluded by Kanda et al., 2004, through inversion analysis of seismic data. Interested in earthquakes, particularly in Asia Pacific and South Asia region, the Nankai Trough, subduction zone related events, tsunami earthquake, intraplate earthquakes. 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. Some sources use the Julian calendar for the earlier earthquakes in the list. 124. 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. This behaviour has been reproduced by modelling the viscoelastic response of the megathrust fault plane with lateral variations in both convergence rate and frictional properties. The working hypothesis is that pressure changes indicate a change in the elastic strain within the formation (Davis et al., 2006). In Kochi prefecture, the Nankai Trough earthquake of magnitude 9.0 class may also occur. This is because the mathematics of this model only used twelve plates, and the Philippine Sea and Eurasian convergent margin were not included. Shortly after the 2011 Tōhoku earthquake, new reports were released which indicated the … The deposits are primarily trench-wedge turbidites (Spinelli et al., 2007). Natural Gas Hydrates: Occurrence, Distribution and Detection. It is the Nankai Trough earthquake that is said to occur there. 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. The Nankai megathrust is thought to have caused at least 12 major earthquakes in the last ca. [6] Nankai Trough Earthquake Information Along the Nankai Trough, megathrust earthquakes with a magnitude 8 or more occur repeatedly. The Nankai trough is also nearing its next earthquake, considering the time lapse of 70 years since the 1946 Nankai earthquake. 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. 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. 145–160. Nankai Trough earthquake risk map. 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 … In order to minimize the damage from the Nankai Trough Earthquake, it is necessary to take countermeasures for liquefaction. Collett, T. S., 2002, Energy resources potential of natural gas hydrates, AAPG Bulletin, v. 86, pp. 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. These five subdivisions show interesting differences in earthquake behavior: 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 features. 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. 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 … 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 earthquakes occur with a return period of about 90–200 years, and often occur in pairs, where a rupture along part of the fault is followed by a rupture elsewhere, notably the 1854 Ansei-Tōkai earthquake and the 1854 Ansei-Nankai earthquake the next day, and the 1944 Tōnankai earthquake, followed by the 1946 Nankaidō earthquake. [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. 534–556. 391–404. 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. [5], The northeasternmost part of the megathrust, segment E, has not ruptured since 1854. 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. 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. Had an unforgettable moment with one back in 2012 . The Nankai Trough is the near-surface extension of a zone of active seismicity that dips beneath SW Japan. As mentioned previously, the NUVEL-1A plate motion model does not include the Philippine Sea plate. According to a government projection, the death toll from a magnitude-9.0 or stronger quake and tsunami occurring along the depression could be as high as 320,000. But it’s always a good idea to be prepared for natural disasters when living in Japan, no matter where you are or how it smells on any given day. [3] However, the trough is potentially a major source of hydrocarbon fuel, in the form of methane clathrate. DeMets, C., Gordon, R., Argus, D., Stein, S., 1990, Current plate motions. However, using the Eurasia to North America plate motion, the estimated rate was 2–4 mm/yr (DeMets et al., 1990). These are generally referred to as Nankai Trough Earthquakes. 252–264. This study estimates that subduction in the Nankai Trough is about 43 mm/yr. 215–226. Analysis of seismic reflection data suggests that some of the displacement is carried by a splay fault dipping at about 25°. [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]. At the targeted site, the geothermal gradient is about four times steeper than elsewhere in the Pacific Ocean. But a big earthquake in the Nankai Trough, or directly below Tokyo, would be an economic shock of global significance. The Nankai Trough is actively deforming and marks a region of seismic activity. In this paper, we report dis-placement rates on the seafloor surface and discuss interplate coupling along the Nankai Trough during the 2, pp 153–177. Furthermore, the short period seismicity appears to have some degree of dependency on bathymetric highs such as seamounts. The Nankai Trough at the bottom of the Pacific Ocean stretches from the Tokai region to Kyushu. The fault is divided into five segments in three zones, which rupture separately or in combination, and depending on location, the resulting earthquakes are subdivided by zone from west to east into Nankai earthquakes, Tōnankai earthquakes, and Tōkai earthquakes. There are indications of an increase in the retention of porosity within the rock. Considering the amount Sella, G., Dixon, T., Mao, A., 2002, REVEL: A model for Recent plate velocities from space geodesy, Journal of Geophysical Research, v. 107, n. B4. Takahashi, N., Kodaira, S., Park, J., Deibold, J., 2003, Heterogeneous structure of western Nankai seismogenic zone deduced by multichannel reflection data and wide-angle seismic data. 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. It would cost as much as 40 per cent of Japan’s gross … Several thrust faults were identified by Operto et al., 2006, of which the thrust faults closest to the subduction zone are active. 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). Krason, 1994, Study of 21 marine basins indicates wide prevalence of hydrates, Offshore, August, 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. Well coring indicates the presence of at least three gas hydrate zones. 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). Furthermore, Pisani et al., 2006, identified protothrusts and decollement surfaces along the Nankai Trough. It is so active that there are a lot of earthquakes. 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). is a submarine trough located south of Japan's island of Honshū, extending approximately 900 km offshore.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). Deformation is concentrated in the outermost imbricate zone, with a significant amount of "out of sequence" thrusting occurring landward. 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 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. 809–819. This article is about earthquakes along the Nankai megathrust fault generally. About Nankai Trough Earthquakes The Nankai Trough is a deep ocean faultline whose northernmost point is Suruga Bay. The Japanese government predicts that an earthquake of immeasurable scale will strike Japan along the Nankai-Trough within the next 30 years. Although Nankai Trough Earthquakes occurred with a roughly 100 - 150 year cycle, they have various repetition intervals and source regions. There was also underground fluid flow with the fluids being much hotter than the present-day temperature of the sediments,[3] which affected mineralization and, potentially, the physical and biological properties of the region. The Nankai Trough is the surface expression of the subduction zone between the Philippine Sea and Amur plates. [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. 1971–92. Krason, 1994, estimated that there are 0.42 to 4.2×1012 cubic meters of methane within the gas hydrates. The northern part of the trough is known as the Suruga Trough, while to the east is the Sagami Trough. 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. This has been attributed to post-depositional opal cementation that is preserving the porosity (Spinelli et al., 2007). 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. This is not in agreement with the REVEL model, seemingly indicating that the NUVEL-1A model may need further revision. Nevertheless as of 2014[update] there is no commercial exploitation. 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. The Nankai Trough is a 700-kilometer-long sea-bottom depression that runs about 100 km off the southern coast from Shizuoka Prefecture to the Shikoku region. The Predicted Nankai Quake", "Catalog of Damaging Earthquakes in the World (Through 2007)", https://en.wikipedia.org/w/index.php?title=Nankai_megathrust_earthquakes&oldid=987944741, Earthquake clusters, swarms, and sequences, Creative Commons Attribution-ShareAlike License, This page was last edited on 10 November 2020, at 04:25. The northeasternmost part of the megathrust, segment E, has not ruptured since 1854. Volti, T., Kaneda, Y., Zatsepin, S., Crampin, S., 2005, An anomalous spatial pattern of shear-wave spitting observed of Ocean Bottom Seismic data above a subducting seamount in the Nankai Trough, Geophysical Journal International, v. 163, pp. The upper portion of the upper accretionary prism and the underlying backstop are currently undergoing a great deal of compressional pressure. 2191–2194. 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. 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). 367–382. 67–86. Despite the uncertainty of when such an earthquake will occur, local authorities are already taking action to prepare … Kastner, 2001, Gas ydrates in convergent margins: formation, occurrence, geochemistry, and global significance. The rupture zone has been subdivided into five areas with respect to seismic modelling (Mitsui et al., 2004). The references used may be made clearer with a different or consistent style of, Learn how and when to remove this template message, "T-Limit of the Deep Biosphere off Muroto", "International Ocean Discovery Program Expedition 370 Preliminary Report", "Hot fluids, burial metamorphism and thermal histories in the underthrust sediments at IODP 370 site C0023, Nankai Accretionary Complex", "Proceedings of the International Ocean Discovery Program Volume 370 Expedition Reports", http://www-odp.tamu.edu/publications/190196SR/211/211_.htm, https://en.wikipedia.org/w/index.php?title=Nankai_Trough&oldid=985827656, Wikipedia references cleanup from September 2009, Articles covered by WikiProject Wikify from September 2009, All articles covered by WikiProject Wikify, Articles containing Japanese-language text, Articles containing potentially dated statements from 2014, All articles containing potentially dated statements, Creative Commons Attribution-ShareAlike License. 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). 85, Fall Meeting Supplements. It occurred on December 21, 1946, at 04:19 JST (December 20, 19:19 UTC). Baba, T., Cummins, P. R., 2005, Contiguous rupture area of two Nankai Trough earthquakes revealed by high resolution tsunami waveform inversion. 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. At depth in the ocean bottoms, in some cases water can form an ice-like solid structure that has methane trapped in its crystalline lattice, forming gas hydrates. 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]. 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. At depth there is an increase in the smectite clay content in the sediments, inferring that there has been a change in the deposition source rock (Steurer et al., 2003). Recently there has been an increase in interest in the release of water from illite clays in subducting sediments. 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. 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). The detrital clays, primarily smectite, display variation over time and location in the Nankai Trough as well as the Shikoku basin. Recent large scale earthquakes resulting from subduction along the Nankai Trough have occurred in areas of large scale increases in the dip angle of the subducting plate (Hori et al., 2004). 245-10, 2005 Salt Lake City Annual Meeting. 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. 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. 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. In this area, the main sedimentological controls for the accumulation of gas hydrates are the sand-rich areas of the trough (Collett, 2002). The data in the news release came from a series of boreholes what were started in the late 1990s. 1980 ). [3] This 'megasplay' fault system has caused an unusually thick section of fluid-rich sedimentary rocks to be deeply underthrust. 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… 73–84. Furthermore, seismic reflection studies have revealed the presence of basement highs that are interpreted as seamounts that are covered in sediments (Ike, 2004). 1300 years. 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.
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