Characteristics Of Tsunamis Research Articles

Tsunami Excitation by Submarine Slides in Shallow-water Approximation

— Landslide-induced tsunamis are receiving increased attention since there is evidence that recent large devastating events have been caused by underwater mass failures. Normally, numerical models are used to simulate tsunami excitation, most of which are based on shallow water, known also as long wave, approximation to the full equations of hydrodynamics. Analytical studies may handle only simplified problems, but help understand the basic features of physical processes. This paper is an analytical investigation of long-water waves excited by rigid bodies sliding on the sea bottom, based on the shallow-water approximation, which is here derived by properly scaling Euler equations for an inviscid, incompressible and irrotational ocean. In one-dimensional (1-D) cases (where motion depends only on one horizontal coordinate), under the further assumptions of small-height slide, which permits the recourse to linear theory, and of flat ocean floor, a solution for arbitrary body shape and velocity is deduced by applying the Duhamel theorem. It is also shown that this theorem can be advantageously used to obtain a general solution in case of a non-flat ocean floor, when the sea bottom follows a special power law, that can be adapted to study reasonable bottom profiles. The characteristics of the excited tsunamis are then evaluated by computing solutions in numerous examples, with special focus on wave pattern and wave evolution. The energy of the wave system is shown to depend on time: it grows expectedly in the initial phase of tsunami generation, when the moving body transfers energy to the water, but it may also diminish later, implying that a certain amount of energy may pass back from water waves to the slide.

Characteristics of Tsunamis Propagating over Oceanic Ridges: Numerical simulation of the 1996 Irian Jaya Earthquake Tsunami

The 1996 Irian Jaya earthquake tsunami was simulated by using the numerical model based on the linear long wave theory including Coriolis force in the spherical coordinate system. The numerical modeling result at Chichijima is in good agreement with the observed tide gauge data. The distinctive oscillation at Chichijima can be interpreted as the formation of boundary waves, so called ridge waves that are excited on the South-Honshu ridge. The mechanism of tsunami propagation trapped on an oceanic ridge is analyzed with the simple ridge model. The result explains the characteristics of ridge waves excited on theSouth-Honshu ridge.

Tsunami Catalog and Zones in Indonesia.

Based on data compiled during the period 1600-1999, 105 tsunami have occurred in Indonesia. Ninety-five events (90%) of them were caused by earthquakes in a shallow region at subduction and plate boundaries, 9 (8%) by volcanic eruption, and one (1%) by a landslide. To clarify the regional characteristics of tsunami, we defined 6 zones; West and East Sunda, Banda, Makassar, Molucca and Irian Jaya, and made the histograms of earthquakes and tsunami by region by decade from 1600 to 1999. Seismic activities were found in East Sunda, Banda and Makassar are high and tsunami activities in West Sunda, Banda, and Molucca. An interval of about 100 years was found for high earthquake and tsunami activities in the period 1800-1999. The percentages of earthquakes accompanied by tsunami to all earthquakes in Banda and Molucca exceed 50%. In terms of human loss due to tsunami, West Sunda is the worst zone because of the devastating damage done by the 1883 Karakatau volcanic eruption. The tsunami potentials in Banda and Molucca in terms of both frequency and damage are very high. Tsunami activity in Banda since 1960 has been remarkably high.

Propagation of Obliquely Incident Tsunamis on a Slope Part II Characteristics of on-Ridge Tsunamis

Fundamental characteristics of tsunamis propagating over an oceanic ridge are investigated analytically based on the linear shallow water wave theory. The oceanic ridge model used has a triangular shape which is formed by the combination of a constant slope and a bottom of uniform depth. Wave pattern of on-ridge tsunamis varies depending on the obliquity of incident waves. Especially, standing waves are formed when the incident wave angle to the ridge exceeds the critical angle. Then no transmitted waves exist because of the evanescent waves. The present study is applied to the 1996 Irian Jaya tsunami which propagated over the South-Honshu ridge. The characteristics of on-ridge tsunamis observed at Chichijima and Hachijojima, which are close to the South-Honshu ridge, can be partly explained by using the solution derived in the present study.

Hydraulic Model Study on Reduction of Runup of Tsunami by Coastal Structures

The object of this investigation is to estimate viability of coastal protection facilities, fishing port construction and so on against tsunami runup. As the first step, we carried out a hydraulic experiment on a detached breakwaters and with no structure. Detached breakwaters were of permeable, impermeable and continuous impermeable varieties. Offshore distance, slope of runup zone and characteristics of tsunami were varied. As a result of the experiment, it was clarified tsunami runup was mainly influenced by the diffraction and that surface elevation around shoreline was influenced by the detached breakwaters and the slope of runup zone. As a whole, the effects of opening width and overflow were great

日本沿岸における1996年6月10日アリューシャン津波の様相

日本沿岸における1996年6月10日アリューシャン津波の様相

1995年10月18日および19日の喜界島近海地震による津波の様相

1995年10月18日および19日の喜界島近海地震による津波の様相

The diatom biostratigraphy of tsunami sediments: Examples from recent and middle holocene events

The interpretation of diatom biostratigraphy is a little used technique in the study of onshore tsunami sedimentation. Evidence is presented from examples from three tsunamis in which sediments were either observed to have been deposited; documentary evidence attests to the presence of sediment sheets, or finally, in the case of palaeo tsunamis, morphological and stratigraphical evidence permits the interpretation of tsunami inundation and the subsequent deposition of sediment. Examples from Scotland and Canada, and preliminary results from Indonesia, illustrate distinctive diatom assemblages that are associated with tsunami sedimentation. These assemblages contrast with the sediments immediately underlying and overlying the tsunami sediment. Data is presented showing an often chaotic assemblage, attributable to the tsunami waves crossing many distinctive diatom habitats, from fully marine planktonic and benthic species, through the varied intertidal zone and finally over the onshore terrestrial environments. The deposits attributable to tsunami inundation, particularly in Scotland, disclose a high proportion (often in excess of 65%) of broken diatom valves, and an over-representation of centric species due to their greater resistance to erosion. Together the information derived from known historical tsunamis and from palaeo tsunamis with good stratigraphical and dating control provide a good basis for the study of the diatom characteristics of modern tsunamis.

琉球列島北部周辺海域における後期完新世の津波特性

琉球列島北部周辺海域における後期完新世の津波特性

小津波の波源モデルと津波の性質

小津波の波源モデルと津波の性質

On tsunami nucleation: 1. A point source

Near‐field tsunami formation is detailed by means of mode summations using point moment tensor sources with a spherically symmetric, self‐gravitating, and elastic earth. Snapshots of vertical sea surface motion calculated within 200 km and 1000 s of an event typically show an initial tsunami pulse slowly grow and then evolve into dispersed wave trains. The general point moment tensor used here produces frequency dependent tsunami radiation patterns of azimuthal degree ≤2. Pure dip and strike slip sources, however, create waves that are symmetric or antisymmetric about the epicenter. With a moment of 1020 N m and a rise time of 25 s, these sources generate initial tsunami pulses 40 km wide when buried 10 km beneath an ocean 4 km deep. Maximum dip slip and strike slip tsunami amplitudes of 209 and 56 cm occur 10 km from the epicenter, 75 s after the start of nucleation. Tsunamis from deeper earthquakes are smaller, broader, and slower to develop because they are depleted of high frequencies. In general, characteristics of tsunamis developing in this dynamic model contradict static concepts which base tsunami formation on permanent deformations of an otherwise rigid seafloor supporting incompressible water. I find that the permanent strain state of the seafloor is not important in tsunami generation because it is defined by frequencies well below the range of interest (100–2000 s)

THE GENERATION OF LONG WAVES IN THE LABORATORY

It became evident in the experimental aspects of a recent study of the propagation of nonlinear long waves past a step and up a slope that it was important to be able to generate waves which were initially well defined. The investigation dealt with the reflection and transmission of tsunamis past the continental shelf-break, and as such, two simple waves were used to represent certain characteristics of tsunamis: solitary waves and cnoidal waves. (Both of these permanent waves are solutions to the Korteweg-de Vries equation which to a certain order describe the propagation in two dimensions of nonlinear dispersive shallow water waves (see, e.g. Whitham, 1974).) The solitary wave actually can be generated in the laboratory in a simple manner if the wave tank is long enough and wave groups trailing the main wave are unimportant to the study. An example of the resulting waves obtained in the laboratory using a crude generation, procedure is demonstrated by the oscillograph record presented in Figure 1. Six traces are shown: the one at the bottom of the figure describes the time-displacement history of a vertical bulkhead wave generator which is moved by a hydraulic-servo system, the other five are the time variations of the water surface obtained using resistance wave gages spaced at the indicated number of depths downstream from the generator. (In the example presented, the depth of water was 10 cm and the wave plate was moved linearly with time a distance of 10.33 cm in 0.8 sec.) The wave generated and first shown 10 depths downstream appears to qonsist of a large wave followed by a series of oscillatory waves (termed the tail). As would be expected, as the waves propagate, due to the frequency content and the amplitude of the waves, the system separates into a leading wave followed some distance behind by the tail. The lead wave has the characteristic shape of a solitary wave. However, if the oscillatory tail is unacceptable for the type of experiments being conducted, and if it cannot be eliminated or the method of elimination is unacceptable, then a means of generation must be sought which eliminates the trailing waves initially.

TSUNAMIS ALONG WEST COAST OF LUZON, PHILIPPINES

A detailed engineering study was made by Ebasco Services, Inc., (1977), for a proposed nuclear power plant in the Napot Point region of Bataan, between the entrance to Manila Bay and Subic Bay, Republic of the Philippines (about 14°- 37-12'N, 120°- 18-3/4'E), Figure 1. As a part of the oceanographic portion of this work, a study was made by the writer of the characteristics of tsunamis that had occurred in the region, and the statistics of occurrence (Wiegel, 1976). The study of tsunamis has been updated to the present time (May, 1980). The location of the site is such that the large tsunamis generated in some areas of the Pacific Ocean (such as off the coasts of Chile, Alaska, Japan and Kamchatka) are not likely to reach Napot Point with any appreciable amplitude (see, for example, Wiegel, 1976). There is good evidence that this is the case. Owing to the relative stability from the standpoint of earthquakes (aseismic) of Borneo, the Malaya Peninsula, most of Indochina and the intervening China Sea (Gutenberg and Richter, 1949, pp. 82 and 93), there is probably little, if any, chance of tsunamis being generated in this region; this appears to be a fact (Berninghausen, 1969). The great eruption of Krakatoa and the tsunami generated by it was not noticed on tide gages at either Singapore or Hong Kong, so that it would be reasonable that it would not have been detected at Manila (Wharton, 1888). Also, the large tsunamis that have been generated in the Sulu Sea and the Celebes Sea do not seem to reach the site with any appreciable amplitude. Thus, the tsunamis of importance to the site are those which will be generated in the local seas off the west coast of Luzon. In order to establish this fact, information is presented on a number of tsunamis generated in other regions, especially those generated in the seas off the west coast of the Philippine Islands.

Tsunami - A Transformed Tectonic Movement

Main characteristics of tsunamis are described here - height and length of waves, speed of travel, period of oscillation etc. The author presumes the tsunami waves follow the block movements of the earth's crust. The beginning of a tsunami is invariable - either the sea water overflows suddenly the coast (following initial upward movement of blocks) or the arrival of a tsunami wave is preceded by a withdrawal of sea (following initial sinking of blocks). The initial movement of the sea water on the coast reflects and transforms only the character of tectonic movements in the adjacent place of the sea-bottom activity. The transgression and/or regression of seawater depends on time when tectonic movements originate. Tlhus the water movement gets complicated.