京都大学 / 0048 / 新制・課程博士 / 博士(地球環境学) / 甲第21241号 / 地環博第177号 / 新制||地環||35(附属図書館) / 京都大学大学院地球環境学舎地球環境学専攻 / (主査)教授 清野 純史, 准教授 小林 広英, 准教授 古川 愛子 / 学位規則第4条第1項該当 / Doctor of Global Environmental Studies / Kyoto University / DFAM

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23455号 / 理博第4749号 / 新制||理||1681(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)准教授 成瀬 元 助教 松岡 廣繁, 教授 生形 貴男 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

In this study, numerical modeling of landslide generated tsunami waves in closed basins and their mechanisms are presented. Historical landslide generated tsunamis are investigated and also the governing parameters affecting impulse wave parameters are studied. The numerical model is based on the solution of nonlinear form of the long wave equations with respect to related initial and boundary conditions. In order to validate the outputs of the modeling by NAMIDANCE, empirical formulation is applied to the same cases as the numerical model and the results are discussed. The numerical model is then applied to Pervari Dam artificial reservoir as a case study to investigate the effects of potential landslide into the reservoir. The outputs of the numerical model are compared with empirical formulation results for different approaches of modeling the landslide effect in water body. The critical sections are observed for overtopping and maximum wave amplitude values and the results are discussed.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24173号 / 理博第4864号 / 新制||理||1696(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)准教授 藤 浩明, 教授 吉川 裕, 教授 石岡 圭一 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

A tsunami generated by the C.E. 1707 Hōei earthquake is largely thought to be the flood event of record for southwestern Japan, yet historical documentation of the event is scarce. This is particularly true in northwestern Shikoku within the Bungo Channel, where significant inconsistencies exist between historical records and model-derived tsunami heights. To independently assess flooding from the C.E. 1707 Hōei tsunami in the context of the region’s long-term flooding history, we present complementary reconstructions of extreme coastal inundation from three back-barrier lakes in the northern Bungo Channel: Lake Ryuuoo, Lake Amida, and Lake Kamega. At all sites, the most prominent marine overwash deposit of the past ~1,000 years, as defined by grain size, density, and geochemical indicators, is consistent with the timing of the 1707 tsunami, providing strong evidence that the event caused the most significant flooding of the last millennium in this region. At Lake Ryuuoo, modern barrier beach elevations and grain sizes in the tsunami’s resultant deposit provide ~4 m as the first physically based height constraint for the 1707 tsunami in the northern Bungo Channel. Around 1,000 years ago, a concurrent and abrupt transition in lithology observed at all three sites is also consistent with rapid, regional geomorphic change. At Lake Ryuuoo, a marine overwash deposit comparable to the 1707 deposit directly overlies this transition. A 1,000-year-old lithological transition or deposit has not been observed at sites closer to the mouth of the Bungo Channel, suggesting that the deposit in Lake Ryuuoo is more consistent with a tsunami generated by local seismicity along the Japan Median Tectonic Line than with a Nankai Trough-derived tsunami. Our findings are significant in that they provide three new millennial-scale tsunami inundation reconstructions for a relatively understudied region of Japan, along with the first physically based height constraint for the Hōei tsunami in the northern Bungo Channel.

The 2004 Indian Ocean tsunami killed over two hundred thousand people in the fifteen countries the tsunami struck. Amidst extensive media coverage, the New Zealand Herald published in excess of two hundred online articles focusing on the event and aftermath. Representations of death and the dead within these articles are often stereotypical and formulaic. Discourse analysis revealed that death and the dead are represented through both metaphorical images and abject descriptions on two distinct scales. Both the bodies and the characters of the dead are handled explicitly according to socially acceptable trends. The dead are also situated spatially with specific identities constructed and reported on. Utilising discourses from throughout the social sciences, analysis of online publications reveals the way perceptions of media consumers to death both inform and are informed by media producers.

The Mw=7.7 tsunamogenic earthquake (TsE) on 17 July 2006, 08:19:28 shock the Indian Ocean at about 15 km depth off-coast Java, Indonesia. It caused a local tsunami with wave heights exceeding 2 m. The death toll reached several hundred. Thousands of people were displaced. By means of standard array methods, we have investigated the propagation and the extent of the rupture front of the causative earthquake. Waveform similarity is expressed by means of the semblance. We back-propagate the semblance for first-arrival phases recorded at broad-band stations within teleseismic distances (30°-95°). Image enhancement is realised by stacking the semblance of 8 arrays within different epicentral and azimuthal directions. From teleseismic observations we find rupturing of a 200 x 100 km wide area in at least 2 phases with propagation from NW to SE and source duration >125 s. The event has some characteristics of a circular rupture followed by unilateral faulting with change in slip rate. Unusually slow rupturing (≈1.5 km/s) is indicated. Fault area and aftershock distribution coincide. Spatial and temporal resolution are frequency dependent. Studies of a Mw6.0 earthquake on 2006/09/21 and one synthetic source show a ≈1° limit in resolution. Retrieved source area, source duration as well as peak values for semblance and beam power increase with the size of the earthquake making possible an automatic detection and classification of large and small earthquakes.

We use seismic array methods (semblance analysis) to image areas of seismic energy release in the Sunda Arc region and world-wide. Broadband seismograms at teleseismic distances (30° ≤ Δ ≤ 100°) are compared at several subarrays. Semblance maps of different subarrays are multiplied. High semblance tracked over long time (10s of second to minutes) and long distances indicate locations of earthquakes. The method allows resolution of rupture characteristics important for tsunami early warning: start and duration, velocity and direction, length and area. The method has been successfully applied to recent and historic events (M>6.5) and is now operational in real time. Results are obtained shortly after source time, see http://www.geo.uni-potsdam.de/Forschung/Geophysik/GITEWS/tsunami.htm). Comparison of manual and automatic processing are in good agreement. Computational effort is small. Automatic results may be obtained within 15 - 20 minutes after event occurrence.

The main topic of this research is the impact to the tsunami-inundated area of the southeast coast of Taiwan caused by earthquakes. According to regression relationship (G-R relation) between the earthquake magnitude and frequency proposed by Gutenberg and Richter (1944), the expected number of tsunamigenic earthquake is estimated. Using the linear shallow water equations of COMCOT (COrnell Multigrid COupled Tsunami model), the propagation of tsunami in the ocean is simulated, and the reciprocal Green's function was applied to save the computing time of COMCOT model. Then, the seismic solution parameters are substituted to acquire a water level distribution of tsunami. Solitary waves of different wave height are used to compute the range and the probability of tsunami inundation at the southeast coast of Taiwan.

This research adopted CMCOT model (Cornell Multi-grid Coupled Tsunami Model) to simulate the wave ran up as the tsunami entered the shoaling water of coastlines, the inundation range on land, and the bridge scour caused by tsunami as it made its way upstream in the rivers. The inundation range was estimated with the fault parameters of Manila Trench and a simulation of bell-sphaped curve waves. The result indicated that if the height of bell-sphaped curve was the same as the maximum water level of the tsunami passed to Kaohsiung offshore, the inundation rage was generally consistent. In the simulation of different water level, we discovered that one meter of wave height was sufficient to inundate the entire coastland of Qijin and Gushan District and that the inundation rage would expand as the wave height increased. With the maximum simulated wave height of six meters, the inundation rage included Gushan, Qijin, Yancheng, Qianjin (small scope), Qianzhen, Fengshan, and Xiaogang District. As to the comparison of historical tsunami, according to the particle size analysis of geological survey from the Kaohsiung Mass Rapid Transit, a layer of fine sediment could be found at specific depth, and its particle size (about 8£r) was significantly different than that of other layers. If this fine sediment was the border of tsunami sediment, the height of historical tsunami wave could be 4.9 meters. With regard to bridge scour, Gwando Bridge was chosen as research area. The result from the sediment simulation of COMCOT model was similar to the scour hole and sediment deposition formed by horseshoe vortex system. Based on the result, the scouring and depositing processes were mainly influenced by the particle size of the sediment. In the simulation, the results of different sediment particle sizes were as follows: (1) If the particle size of sediment was greater than 62£gm, the maximum scour depth was less than 4 cm, and the maximum height of deposition was under 3 cm. (2) If the particle size of sediment was between 4 and 62£gm, the maximum scour depth was between 4 and 5 cm, and the maximum height of deposition was between 3 and 4 cm. (3) If the particle size of sediment was smaller than 4£gm, the maximum scour depth was above 6.8 cm, and the maximum height of deposition was greater than 5 cm.