[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. Tanioka, Y., Kusunose, T., Babu, T., Haseqawa, Y., 2004, Large earthquake along the Nankai trough, the 1944 Tanankai earthquake (Mw 8.0) and two 2004 Tonankai-oki earthquakes (Mw 7.2 and 7.4). Analysis of seismic reflection data suggests that some of the displacement is carried by a splay fault dipping at about 25°. 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. 67–86. [8], The Japanese government estimates that a major earthquake on the Nankai Trough would cause 169.5 trillion yen in direct damage and 50.8 trillion yen in economic losses for the following year. 1300 years. along the Nankai Trough subduction zone in Japan, large earthquakes have occurred every century or so with a low coefficient of variation on the mean recurrence interval (Sykes and Menke, 2006), with the most recent large earthquakes as part of a sequence in 1944 and 1946. 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. Had an unforgettable moment with one back in 2012 . 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. 2191–2194. 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. 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. Nevertheless as of 2014[update] there is no commercial exploitation. Honshu itself is formed from the island arc developed over the subducting plate. 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. DeMets, C., Gordon, R., Argus, D., Stein, S., 1990, Current plate motions. REVEL-based calculations indicate that there is no accumulation of strain at the trench. It is so active that there are a lot of earthquakes. 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. More earthquake news on Strange Sounds and Steve Quayle. American Geophysical Union Washington, DC, pp. 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 … [9] A death toll as high as 230,000 has been suggested for such an event.[10]. 252–264. 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. On all but one occasion, rupture of segment C (±D ±E) has been followed by rupture of segments A+B within a few years. Although Nankai Trough Earthquakes occurred with a roughly 100 - 150 year cycle, they have various repetition intervals and source regions. [7] Colwell, F., Matsumoto, R., Reed, D., 2004, A Review of gas hydrate, geology and biology of the Nankai Trough, Chemical Geology, v. 205, pp. Nankai Trough Earthquake Information Along the Nankai Trough, megathrust earthquakes with a magnitude 8 or more occur repeatedly. Recently there has been an increase in interest in the release of water from illite clays in subducting sediments. Collett, T. S., 2002, Energy resources potential of natural gas hydrates, AAPG Bulletin, v. 86, pp. This has been attributed to post-depositional opal cementation that is preserving the porosity (Spinelli et al., 2007). Seismically, the high bottom simulating reflectors are considered indicative of gas hydrates (Colwell et al., 2004). The Nankai Trough is the near-surface extension of a zone of active seismicity that dips beneath SW 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). The information concerning the gas hydrates in the Nankai Trough was initially published in 2000 by the Japan National Oil Corporations. The deposits are primarily trench-wedge turbidites (Spinelli et al., 2007). Saffer, D., Underwood, M., McKiernan, A., 2005, Smectitie transformation in the Nankai trough: Effects on subduction zone mechanics and hydrogeology, Paper, No. 73–84. At the targeted site, the geothermal gradient is about four times steeper than elsewhere in the Pacific Ocean. 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. This area was not in the original NUVEL models (DeMets et al., 1990). 215–226. 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. The Nankai trough runs roughly parallel to the Japan Median Tectonic Line. This is not in agreement with the REVEL model, seemingly indicating that the NUVEL-1A model may need further revision. The rupture zone has been subdivided into five areas with respect to seismic modelling (Mitsui et al., 2004). The earthquake repeat intervals are generally in the range 90–200 years. 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. But a big earthquake in the Nankai Trough, or directly below Tokyo, would be an economic shock of global significance. 2, pp 153–177. Some sources use the Julian calendar for the earlier earthquakes in the list. The northern part of the trough is known as the Suruga Trough, while to the east is the Sagami Trough. Furthermore, Pisani et al., 2006, identified protothrusts and decollement surfaces along the Nankai Trough. IODP Expeditions drilled the accretionary complex of the Nankai Trough and reveal the thermal history with drill core analyses. 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. The Nankai Trough is a very large ditch located in the seabed south of Shikoku. 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). 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). [3] However, the trough is potentially a major source of hydrocarbon fuel, in the form of methane clathrate. The Nankai Trough is an ocean-floor trench which runs underneath the Pacific Ocean off the coast of Japan from Shizuoka to Kyūshū, where the … 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). 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. Several thrust faults were identified by Operto et al., 2006, of which the thrust faults closest to the subduction zone are active. Despite the uncertainty of when such an earthquake will occur, local authorities are already taking action to prepare … 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 … Rapid sedimentation resulted in a greater retention of heat. 243302450. 245-10, 2005 Salt Lake City Annual Meeting. 88–100. 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. 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. 85, Fall Meeting Supplements. This article is about earthquakes along the Nankai megathrust fault generally. 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. 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 Nankai megathrust is thought to have caused at least 12 major earthquakes in the last ca. 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. Hori, T., Kato, N., Hirahara, K., Baba, T., Keneda, Y., 2004, A numerical simulation of earthquake cycles along the Nakai Trough in southwest Japan: lateral variation in frictional property due to the slab geometry controls the nucleation position, Earth and Planetary Science Letter, v. 22, 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. 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. However, there is an anomalous preservation of porosity at depth at drill site 1173. Along the Nankai Trough in western Japan, where recurring interplate megathrust earthquakes have occurred (5, 6) and which has a dense seismic and geodetic monitoring network, their interrelationships have been discussed and compared in detail (4, 7–10). In this paper, we report dis-placement rates on the seafloor surface and discuss interplate coupling along the Nankai Trough during the Muramatsu, Y., Doi, T., Tomaru, H., Fehn, U., Takeuchi, R., Matsumote, R., 2006, Hologen concentrations in pore waters and sediments of the Nankai, Trough, Japan: Implications for the origin of gas hydrates, Applied Geochemistry, v. 22, pp. Furthermore, there is a geothermal alteration of the smectite, converting it to illite clay (Steurer et al., 2003). This study estimates that subduction in the Nankai Trough is about 43 mm/yr. 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. 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 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. 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. [1] Its thermal history is complex due to multiple heating events or property changes. The rupture zone has been subdivided into five areas with respect to seismic modelling (Mitsui et al., 2004). The Nankai Trough is the surface expression of the subduction zone between the Philippine Sea and Amur plates. A seaward change in the pressure as measured by the borehole instruments likely indicates a relaxation of the sediments from the previous major thrust earthquake. 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. The Japanese government predicts that an earthquake of immeasurable scale will strike Japan along the Nankai-Trough within the next 30 years. Nankai Trough earthquake risk map. The Nankai Trough is actively deforming and marks a region of seismic activity. A biennial survey by Shizuoka Prefecture showed in 2017 that the percentage of residents “very interested” in the Nankai Trough or Tokai earthquakes stood … This was concluded by Kanda et al., 2004, through inversion analysis of seismic data. It occurred on December 21, 1946, at 04:19 JST (December 20, 19:19 UTC). 11, pp. 34–35. 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. 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 Nankai Trough at the bottom of the Pacific Ocean stretches from the Tokai region to Kyushu. 124. 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. It would cost as much as 40 per cent of Japan’s gross … In Kochi prefecture, the Nankai Trough earthquake of magnitude 9.0 class may also occur. The recent magnitude 7.3 earthquake on the southern island of Kyushu, which killed at least 49 people and destroyed thousands of homes, is a reminder that Japan remains exposed to frequent natural disasters. Baba, T., Cummins, P. R., 2005, Contiguous rupture area of two Nankai Trough earthquakes revealed by high resolution tsunami waveform inversion. 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. Krason, 1994, Study of 21 marine basins indicates wide prevalence of hydrates, Offshore, August, pp. In one recorded case (the 1707 Hōei earthquake) the fault ruptured along its entire length. 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. In this area, the main sedimentological controls for the accumulation of gas hydrates are the sand-rich areas of the trough (Collett, 2002). Furthermore, the short period seismicity appears to have some degree of dependency on bathymetric highs such as seamounts. The northeasternmost part of the megathrust, segment E, has not ruptured since 1854. 1980 ). Furthermore, seismic reflection studies have revealed the presence of basement highs that are interpreted as seamounts that are covered in sediments (Ike, 2004). Obana, K., Kodaira, S., Kaneda, Y., 2006, Seismicity related to heterogeneous structure along the western Nankai trough off Shikoku Island, Geophysical Research Letters. 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. 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. Pisani, P., Reshef, M., Moore, G., 2005, Targeted 3-D prestack depth imaging at Legs 190-196 ODP drill sites (Nankai Trough, Japan). Typically porosity decreases with increasing depth. 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). However, a more recent study that included the Philippine Sea plate was based on data from the NUVEL-1A model (Zang et al., 2002). 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… This page was last edited on 28 October 2020, at 05:11. 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. Interested in earthquakes, particularly in Asia Pacific and South Asia region, the Nankai Trough, subduction zone related events, tsunami earthquake, intraplate earthquakes. [3] As basin formation stopped and sedimentation took place, the sediments acted like a blanket to trap the heat below. The detrital clays, primarily smectite, display variation over time and location in the Nankai Trough as well as the Shikoku basin. 1015–1018. 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 Nankai accretionary complex is an area with high heat flow. 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). Using recent ocean bottom seismograph studies, it has been determined that most of the seismicity occurs near the trough axis (Obana et al., 2006). 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. 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. 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. 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). Considering the amount 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. 367–382. Davis, E., Becker, K., Wang, K., Obara, K., Ito, Y., Kinoshita, M., 2006, A discrete episode of seismic and aseismic deformation of the Nankai trough subduction zone accretionary prism and incoming Philippine Sea plate, Earth and Planetary Science Letter 242, pp. 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). 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. 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 because the mathematics of this model only used twelve plates, and the Philippine Sea and Eurasian convergent margin were not included. The upper portion of the upper accretionary prism and the underlying backstop are currently undergoing a great deal of compressional pressure. There are indications of an increase in the retention of porosity within the rock. All the dates shown in the table use the Gregorian calendar. 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. The Nankai Trough is the near-surface extension of a zone of active seismicity that dips beneath SW Japan. 809–819. 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. Historically, the most recent large-scale earthquake to occur in the Nankai Trough was in 1944 off the Kii Peninsula. [4] The area was originally a basin (Shikoku Basin) with active hydrothermal activity during its formation. The 1946 Nankai earthquake (昭和南海地震 Shōwa Nankai jishin) was a great earthquake in Nankaidō, Japan. [6] 391–404. 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