A revised tsunami source model for the 1707 Hoei earthquake and simulation of tsunami inundation of Ryujin Lake, Kyushu, Japan (original) (raw)
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Pure and Applied Geophysics PAGEOPH, 1995
Heterogeneous fault motion of the 1993 Hokkaido Nansei-Oki earthquake is studied by using seismic, geodetic and tsunami data, and the tsunami generation from the fault model is examined. Seismological analyses indicate that the focal mechanism of the first 10 s, when about a third of the total moment was released, is different from the overall focal mechanism. A joint inversion of geodetic data on Okushiri Island and the tide gauge records in Japan and Korea indicates that the largest slip, about 6 m, occurred in a small area just south of the epicenter. This corresponds to the initial rupture on a fault plane dipping shallowly to the west. The slip on the northernmost subfault, which is dipping to the east, is about 2 m, while the slips on the southern subfaults, which are steeply dipping to the west, are more than 3 m. Tsunami heights around Okushiri Island are calculated from the heterogeneous fault model using different grid sizes. Computation on the smaller grids produces larger tsunami heights that are closer to the observed tsunami runup heights. Tsunami propagation in the nearly closed Japan Sea is examined as the free oscillation of the Japan Sea. The excitation of the free oscillation by this earthquake is smaller than that by the 1964 Niigata or 1983 Japan Sea earthquake. , show that the maximum tsunami runup height was 32 m on Okushiri Island and that the entire island subsided by 5-80 cm.
Effects of the Tsunami Generated by the 1662 Hyuga-Nada Earthquake off Miyazaki Prefecture, Japan
Pure and Applied Geophysics
The Hyuga-nada region is located in the southwestern part of the Nankai Trough in the Pacific Ocean, where M7 class interplate earthquakes have been repeatedly occurring because of the subduction of the Philippine Sea Plate. The largest earthquake recorded in history for the Hyuga-nada region was the Hyuga-nada earthquake of 1662, which occurred off Miyazaki Prefecture in the southeastern area of Kyushu region, Japan, generating a tsunami. The region is also an area where slow earthquakes are active at the shallow part of the plate boundary. It is confirmed by the 2011 Tohoku earthquake that the active area of shallow slow earthquakes also became a tsunami source area. We hypothesize that the unusually large tsunami of 1662 was caused by the coseismic slipping of the active source area of shallow slow earthquakes. We constructed the fault model of the 1662 Hyuga-nada earthquake based on recent geophysical observations. A numerical simulation of the tsunami was carried out using the ...
Amplification of tsunami heights by delayed rupture of great earthquakes along the Nankai trough
Earth, Planets and Space, 2010
We investigated the effect of delayed rupture of great earthquakes along the Nankai trough on tsunami heights on the Japanese coast. As the tsunami source, we used a model of the 1707 Hoei earthquake, which consists of four segments: Tokai, Tonankai, and two Nankai segments. We first searched for the worst case, in terms of coastal tsunami heights, of rupture delay time on each segment, on the basis of superposition principle for the linear long wave theory. When the rupture starts on the Tonankai segment, followed by rupture on the Tokai segment 21 min later, as well as the eastern and western Nankai segments 15 and 28 min later, respectively, the average coastal tsunami height becomes the largest. To quantify the tsunami amplification, we compared the coastal tsunami heights from the delayed rupture with those from the simultaneous rupture model. Along the coasts of the sea of Hyu'uga and in the Bungo Channel, the tsunami heights become significantly amplified (> 1.4 times larger) relative to the simultaneous rupture. Along the coasts of Tosa Bay and in the Kii Channel, the tsunami heights become amplified about 1.2 times. Along the coasts of the sea of Kumano and Ise Bay, and the western Enshu coast, the tsunami heights become slightly smaller for the delayed rupture. Along the eastern Enshu coast, the coast of Suruga Bay, and the west coast of Sagami Bay, the tsunami heights become amplified about 1.1 times.
Fault models of unusual tsunami in the 17th century along the Kuril trench
Earth Planets and Space, 2008
Geologic evidence has shown that unusual tsunami deposits are traced as high as 18 m above the current sea level or as far as 1-4 km inland from the shoreline on the Pacific coast of eastern Hokkaido, and that such unusual tsunamis have recurred at about 500 year interval with the most recent event in the 17th century. We computed coastal tsunami heights along the Hokkaido and Sanriku coasts and inundation at five coastal marshes in Hokkaido where the tsunami deposits were mapped. Three types of faults were tested: giant fault, tsunami earthquake and interplate earthquake models. The giant fault model, with the largest seismic moment, yields the lowest tsunami heights and smaller inundation than the distribution of tsunami deposits in Hokkaido, while the tsunami heights are largest in Sanriku. The tsunami earthquake model yields little inundation in Hokkaido and the smallest heights in Sanriku. The interplate earthquake model produces the largest tsunami heights and inundation in Hokkaido, reproducing the distribution of tsunami deposits on the Nemuro coast. The multi-segment interplate earthquake with variable slip (10 m on Tokachi and 5 m on Nemuro segment) can reproduce the distribution of tsunami deposits on the Tokachi coast as well, and considered as the best source model for the 17th century tsunami, although the Sanriku tsunami heights are more than 3 m, exceeding an inferred detection threshold of historical documents. The seismic moment is estimated as 8 × 1021 N m (Mw 8.5). Comparison with the recent 2003 Tokachi-oki earthquake indicates that the 17th century tsunami source was longer and located further offshore at shallower depth.
Overview of Holocene Tsunami Deposits along the Nankai, Suruga, and Sagami Troughs, Southwest Japan
Pure and Applied Geophysics, 2007
Tsunami deposits provide a basis for reconstructing Holocene histories of great earthquakes and tsunamis on the Pacific Coast of southwest Japan. The deposits have been found in the past 15 years at lakes, lagoons, outcrops, and archaeological excavations. The inferred tsunami histories span 3000 years for the Nankai and Suruga Troughs and nearly 10,000 years for the Sagami Trough. The inferred histories contain recurrence intervals of variable length. The shortest of these -100-200 years for the Nankai Trough, 150-300 years for the Sagami Trough -resemble those known from written history of the past 1000-1500 years. Longer intervals inferred from the tsunami deposits probably reflect variability in rupture mode, incompleteness of geologic records, and insufficient research.
Earth-Science Reviews, 2016
The Nankai-Suruga Trough, the subduction zone that lies immediately south of Japan's densely populated southern coastline, generates devastating great earthquakes (magnitude > 8) characterised by intense shaking, crustal deformation and tsunami generation. Forecasting the hazards associated with future earthquakes along this >700 km long fault requires a comprehensive understanding of past fault behaviour. While the region benefits from a long and detailed historical record, palaeoseismology has the potential to provide a longer-term perspective and additional crucial insights. In this paper, we summarise the current state of knowledge regarding geological evidence for past earthquakes and tsunamis along the Nankai-Suruga Trough. Incorporating literature originally published in both Japanese and English and enhancing available results with new age modelling approaches, we summarise and critically evaluate evidence from a wide variety of sources. Palaeoseismic evidence includes uplifted marine terraces and biota, marine and lacustrine turbidites, liquefaction features, subsided marshes and tsunami deposits in coastal lakes and lowlands. While 75 publications describe proposed evidence from more than 70 sites, only a limited number provide compelling, well-dated evidence. The best available records enable us to map the most likely rupture zones of twelve earthquakes that occurred during the historical period. This spatiotemporal compilation suggests that the AD 1707 earthquake ruptured almost the full length of the subduction zone and that earthquakes in AD 1361 and 684 may have been predecessors of similar magnitude. Intervening earthquakes were of lesser magnitude, highlighting the variability in rupture mode that characterises the Nankai-Suruga Trough. Intervals between ruptures of the same seismic segment range from less than 100 to more than 450 years during the historical period. Over longer timescales, palaeoseismic evidence suggests intervals between earthquakes ranging from 100 to 700 years, however these figures reflect a range of thresholds controlling the creation and preservation of evidence at any given site as well as the genuine intervals between earthquakes. At present, there is no geological data that suggest the occurrence of a larger magnitude earthquake than that experienced in AD 1707, however few studies have sought to establish the relative magnitudes of different earthquake and tsunami events along the Nankai-Suruga Trough. Alongside the lack of research designed to quantify the maximum magnitude of past earthquakes, we emphasise issues over alternative hypotheses for proposed palaeoseismic evidence, the paucity of robust chronological frameworks and insufficient appreciation of changing thresholds of evidence creation and preservation over time as key issues that must be addressed by future research.
Earth, Planets and Space
Tsunami deposits were collected along the coast of southwestern Hokkaido and Okushiri Island, northern Japan. The distribution of these deposits suggested that large earthquakes and tsunamis have repeatedly occurred off southwestern Hokkaido. Along the southern coast of Okushiri Island, five tsunami sand/gravel layers have been deposited during the last 3000 years. The latest was deposited by the 1741 Oshima-Oshima landslide tsunami and the second by the 12th century tsunami. The later tsunami was probably generated by a large earthquake because submarine seismo-turbidites with similar age exist in the region and a large inland landslide had occurred in Okushiri Island in approximately the 12th century. The ages of paleo-tsunami events prior to the 12th century are 1.5-1.6, 2.4-2.6, 2.8-3.1 ka. In this study, a fault model of the 12th century earthquake was estimated by comparing tsunami deposit distributions and calculated tsunami inundation areas at five sites in Okushiri Island and Hiyama region. Fault model F17, a submarine active fault in the Japan Sea near Oshima-Oshima, is a probable source for this tsunami. Numerical simulation of the tsunami was performed based on fault model F17; we modified the fault parameters (length and slip amount) from the original model to explain tsunami deposit distributions. A shorter length of 104 km and a larger slip amount of 18 m were appropriate for the fault model on the basis of parametric studies. The seismic moment of the earthquake was calculated to be 9.95 × 10 20 Nm (M w 7.9) assuming a rigidity of 3.43 × 10 10 N/m 2. The estimated fault model is located between the focal regions of the 1993 Hokkaido Nansei-oki earthquake and the 1983 Japan Sea earthquake.
Tsunamigenic Source Mechanism and Efficiency of the March 11, 2011 Sanriku Earthquake in Japan
2011
The great Tohoku earthquake of March 11, 2011 generated a very destructive and anomalously high tsunami. To understand its source mechanism, an examination was undertaken of the seismotectonics of the region and of the earthquake’ focal mechanism, energy release, rupture patterns and spatial and temporal sequencing and clustering of major aftershocks. It was determined that the great tsunami resulted from a combination of crustal deformations of the ocean floor due to up-thrust tectonic motions, augmented by additional uplift due to the quake’s slow and long rupturing process, as well as to large coseismic lateral movements which compressed and deformed the compacted sediments along the accretionary prism of the overriding plane. The deformation occurred randomly and non-uniformly along parallel normal faults and along oblique, en-echelon faults to the earthquake’s overall rupture direction ‐ the latter failing in a sequential bookshelf manner with variable slip angles. As the 1992 ...