Tsunami source consideration of the 1662 Hyuga-nada earthquake occurred off Miyazaki Prefecture, Japan (original) (raw)
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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 ...
Tsunami generation of the 1993 Hokkaido Nansei-Oki earthquake
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.
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 ...
Physics of the Earth and Planetary Interiors, 1985
The source process of the Japan Sea earthquake of May 26, 1983 is studied by using the long-period surface waves and tsunamis. The moment tensor inversion of Rayleigh waves which consider the lateral heterogeneity of the Earth is developed and applied to the IDA records of this event. The moment tensor solution and first-motion data indicate that the mechanism is dip-slip and the seismic moment is 7.6 x 1027 dyne-cm. The fault is estimated to be 120 km in length. 40 km in width, and dips eastward with a dip angle of 30°from the aftershock distribution. Tsunami simulation for an actual topography is made to restrain the slip on the fault. The aftershock area and the tsunami records suggest that the fault is divided into two segments. The northern part strikes NNW and slips 4 m, while the southern part strikes NNE and slips 5 m. The fault geometry, the aspect ratio, and the stress drop of this event are similar to those of the 1964 Niigata earthquake, but differ from those of the earthquakes in the Pacific coast of Japan.
Analysis of the tsunami generated by the 2007 Noto Hanto earthquake
Earth, Planets and Space, 2008
The 2007 Noto Hanto earthquake generated a small tsunami that was recorded at several tide gauge stations along the coast of the Japan Sea. The most important feature of this tsunami is that two waveforms recorded at the Wajima and Noto tide gauge stations, which are located 30 km apart, showed very different later phases-the large later phases recorded at Noto were not observed at Wajima. Numerical simulation of the tsunami indicated that the difference was caused by the shallow water bathymetry around the Noto peninsula. The large tsunami that was amplified at a few tens of kilometers off the north coast of the Noto peninsula propagated towards the Noto tide gauge station, but not towards the Wajima station. This study indicates that the propagation of a tsunami caused by a shallow earthquake beneath a coastal area is significantly affected by the local bathymetry. A comparison of the observed and computed tsunami waveforms indicated that the slip amount of the fault was 0.8 m. The seismic moment of the Noto Hanto earthquake was calculated to be 0.94 × 10 19 N m (M w 6.6).
Reconsideration of the Source Model for the 1662 Hyuga-nada Earthquake
2020
The 1662 Hyuga-nada Earthquake is one of the largest earthquakes to have occurred in the Hyuga-nada region, Southwest Japan, rupturing the western part of the Nankai Trough subduction zone. Strong ground motion and a large tsunami with an estimated height of at least 4–5 m were reported along the coast of Miyazaki Prefecture, Kyushu Island, with extensive damage reported across this region. Therefore, developing a more complete picture of the 1662 Hyuga-nada Earthquake will improve our understanding of tsunami risk along the Pacific coast of Southwest Japan. Here we use the most recent geophysical data from the region to propose a novel source model for the 1662 Hyuga-nada Earthquake that incorporates our current understanding of the interactions between slow earthquakes and great earthquakes. The source area in our proposed model extends from the focal region of recurrent M7-class interplate earthquakes to the region of slow earthquakes that occur at relatively shallow depths along...
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.
Abnormal tsunamis caused by the June 13, 1984, Torishima, Japan, earthquake
Journal of Geophysical Research: Solid Earth, 1991
An earthquake with an MS = 5.6 (mb=5.5) which occurred near Torishima, Japan, on June 13, 1984, generated abnormally large tsunamis (tsunami magnitude Mt = 7.3) for its relatively small earthquake magnitude. The maximum amplitude of the tsunamis is not a simple function of distance as the magnitude formula implies. In order to quantify the abnormal tsunamis, we modeled the tsunami source using a finite difference computation on the actual bathymetry. The source of these abnormal tsunamis is modeled as a water surface displacement, with a radius of 12 km and maximum water height of 13 cm. The displaced water volume is 4×1013 cm3, and the potential energy is calculated as 2×1017 ergs. If this water displacement is due to a fault motion at 5 km depth, a moment magnitude Mw is estimated to be 6.3. This value is larger than Mw estimated from seismic waves by 0.7, but smaller than Mt by 1.0. The former difference suggests that the earthquake source is very different from an ordinary fault...
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.
Mechanism of the 2015 volcanic tsunami earthquake near Torishima, Japan
Science advances, 2018
Tsunami earthquakes are a group of enigmatic earthquakes generating disproportionally large tsunamis relative to seismic magnitude. These events occur most typically near deep-sea trenches. Tsunami earthquakes occurring approximately every 10 years near Torishima on the Izu-Bonin arc are another example. Seismic and tsunami waves from the 2015 event [ (moment magnitude) = 5.7] were recorded by an offshore seafloor array of 10 pressure gauges, ~100 km away from the epicenter. We made an array analysis of dispersive tsunamis to locate the tsunami source within the submarine Smith Caldera. The tsunami simulation from a large caldera-floor uplift of ~1.5 m with a small peripheral depression yielded waveforms remarkably similar to the observations. The estimated central uplift, 1.5 m, is ~20 times larger than that inferred from the seismologically determined non-double-couple source. Thus, the tsunami observation is not compatible with the published seismic source model taken at face val...