Simulation Of Tsunami Propagation Research Articles

Three‐dimensional simulation of tsunami generation and propagation: Application to intraplate events

A parallel finite difference numerical simulation program based on the Navier‐Stokes (NS) equations is developed for simulating 3‐D tsunami generation and propagation. We can simulate tsunami propagation over more than 1000 km using this program, although such tsunami propagation over long distances has usually been conducted on the basis of on 2‐D simulations. Some 2‐D simulations have assumed that the initial tsunami distribution is identical to the sea bottom deformation caused by the earthquake. The 3‐D simulations, however, indicate that this assumption is inappropriate when the source width 2ax is less than 10 times the sea depth h (2ax < 10h) for a source process time of 20 s. Dispersion of tsunami appears when the source is of small size, and the dispersion is more apparent in a direction perpendicular to the fault strike. We also conduct tsunami simulations for two intraplate events: the 2004 off–Kii Peninsula (M 7.4) and the 2007 off–Kuril Islands (M 8.1) events. The 3‐D tsunami simulation has successfully simulated the offshore tsunami, and we obtained good agreement between the observations and the calculations for both events. In particular, for the 2004 off–Kii Peninsula event, although the 2‐D linear long‐wave theory cannot simulate important characteristics in the record such as the arrival time of the peak amplitude and the dispersive tsunami, the 3‐D NS simulation is well able to model those characteristics.

Evaluation of Tsunami Risk Posed to Sri Lanka by Potential Mega-Thrust Earthquakes in the Makran Subduction Zone

This paper is concerned with a numerical study carried out to assess the threat posed to Sri Lanka by potential tsunamigenic earthquakes in the Makran subduction zone in the Arabian Sea off the south coasts of Pakistan and Iran. The fault plane model adopted in the present simulations corresponds to a worst-case scenario of simultaneous rupture of the entire eastern segment of the Makran Trench. A hydrodynamic model based on linear shallow-water equations was employed to simulate tsunami propagation from the source to the shoreline around Sri Lanka. The numerical simulations suggest that the maximum nearshore tsunami amplitudes along the coastal belts of the Western, North-Western and Southern Provinces are of the order of 1 m; the corresponding values for the Eastern and Northern provinces are even smaller, about 0.2 m and 0.1 m, respectively. The model results also indicate that the tsunami waves will first hit the coastal belt of the Western Province about 280 minutes after the earthquake, followed by Southern and North-Western Provinces. The results presented in this paper would be useful for authorities responsible for evacuation to make a better judgement as to the level of threat in different areas along the coastline, and to act accordingly, if a large earthquake were to occur in the Makran subduction zone.

Applicability of the Lattice Boltzmann Method for Tsunami Modeling

The Lattice Boltzmann Method (LBM) is one of the robust CFD models to solve the fluid dynamics. In the present study, the LBM for the Shallow Water Equations is developed to simulate tsunami propagation and coastal inundation. The offshore boundary conditions and nesting technique for multi-scale grid are developed for practical use of LBM. The model is validated, for a potential tsunami scenario by the comparison with the Finite Difference Method. The results imply that LBM has a sufficient accuracy and robustness for tsunami propagation and inundation modeling.

Numerical simulation of tsunami propagation using the characteristic-based split method

Numerical simulation of tsunami propagation using the characteristic-based split method

An Efficient and Robust Tsunami Model on Unstructured Grids. Part I: Inundation Benchmarks

A modern multi-purpose baroclinic circulation model (SELFE) has been recently extended to include the ability to simulate tsunami propagation and inundation. The core model is based on the 3-D nonlinear shallow-water wave (NSW) equations, which are solved on unstructured grids, using the finite-element method. A semi-implicit method is used to solve all equations to enhance numerical stability, thus bypassing the most stringent CFL restriction on the time step. Further aided algorithmically by an Eulerian-Lagrangian solution of the advection terms in the momentum equation and by a simple yet effective inundation algorithm, SELFE is very efficient and robust in both quasi-2-D (with two vertical layers) and 3-D modes. A quasi-2-D version of the model is being used to update and expand the characterization of tsunami hazards along the Oregon coast. As a part of a rigorous testing procedure that includes multiple types of coastal problems, we present in this paper a quantitative assessment of performance of the quasi-2-D SELFE for two challenging open benchmark problems proposed in the 3rd International Workshop on Long-wave Runup Models. Satisfactory results are obtained for both problems.

Field survey and numerical simulation of the 21 November 2004 tsunami at Les Saintes (Lesser Antilles)

Although a few historical tsunamis have occurred in the Lesser Antilles region, their characteristics are poorly documented due to the ephemeral nature of the associated signatures. Recently, a tsunami was generated following a magnitude Mw 6.3 earthquake that occurred on 21 November 2004 between Guadeloupe and Dominica. This was one of the two largest historical earthquakes recorded in this area in the last century. A field survey allowed us to characterize the tsunami which affected Les Saintes, the southern coast of Basse‐Terre (Guadeloupe) and northern Dominica. We used these data to constrain a numerical simulation of tsunami generation and propagation. The 21 November tsunami provides a unique opportunity to further constrain the models of brittle deformation in the back arc region proposed by previous tectonic investigations, to characterize the tsunami signatures and to improve regional hazards evaluation.

A Study for the Sediment Transport due to Tsunami along the Natural Coast

In this study, we investigated the sediment transport due to the 2004 Indian ocean tsunami along the natural coast at Hambantota, Sri-lanka. Bathymetry and topography surveys before and after the tsunami were conducted and the results showed significant erosion by the tsunami, especially around the places where shoreline discontinuations were observed. We conducted a numerical simulation of tsunami propagation as well as the bathymetry change induced by the tsunami. Furthermore, we also estimated the bathymetry change due to the usual sea waves at the coast. Our numerical results suggested that the tsunami has strong bottom shear stress at specific landform such as a river mouth and a cape. We also found that the sediment erosion and accumulation due to the tsunami had been mitigated by usual sea waves after the tsunami.

An Experimental Study on Tsunami Generation due to Landslides

Hydraulic experiments were performed to simulate tsunami generation due to landslides, which consist of particles including glass balls, glass beads, natural rocks, acrylic rocks, and block ices, as well as packages of glass balls. The gate can be opened smoothly and quickly by pushing down two levers connected with the gate plate. The period of tsunamis due to glass-bead motion is longer than that due to glass-ball motion. On a mild slope, tsunami profiles depend on the diameter of the sliding glass balls. In shallow water, the slide distance of particles is shorter, the tsunami height becomes lower. The block ices can also generate large tsunamis, although the ice does not go deep under the water.

Sensitivity tests on relations between tsunami signal and seismic rupture characteristics: The 26 December 2004 Indian Ocean event case study

The long wave elevation of a tsunami is closely related to the characteristics of its triggering source. Tide gauges, sea level anomaly altimeters can all be used to measure the amplitude of the wave. Numerical modeling can also be used to approximate tsunami propagation based upon a certain parameterisation of the source describing the mode of generation. Once a robust numerical model has been developed, the simulated wave sequence and the various hydrodynamic observations can be compared to develop a better characterization of the tsunami source. This procedure may be used to refine the description of a tsunami source derived from seismological instrumentations. Numerical sensitivity tests of a tsunami propagation model were used to address whether a simple tide gauge record may help in better identifying the nature of the rupture process. Specifically, four different pure thrust faultings – reverse/normal faults and two opposite dipping orientations – of the 26 December 2004 Indian Ocean tsunami were simulated. The model chosen for the investigation used the representation of Okada, Y., [1985. Surface deformation due to shear and tensile faults in a half-space. Bull. Seism. Soc. Am. 75 (4), 1135–1154] to describe the rupture process and the Funwave numerical model to simulate tsunami propagation. The author finds that it is possible to identify the best-fitted scenario among the four, depending on the nature of the leading wave (crest or trough) and the ratio between the first crest amplitudes. It depends, however, on the dipping amount as the trough/crest dipole reverses at around 43°. Consequently, the depth of the earthquake (location of the epicenter within the interplate slab) also controls the nature of the leading wave (crest or depression).

Characteristic period of Tsunami in Seto Inland Sea

It is very important for tsunami disaster prevention in the coastal area of Shikoku Island to clarify a mechanism of tsunami propagation in the Seto Inland Sea. Especially, a resonance of tsunami is a dominant factor in such a narrow inland sea. In this study, numerical simulation of tsunami propagation is executed to estimate tsunami height and characteristic period in the Seto Inland Sea. According to the numerical analysis, a tsunami height does not decline during about 10 hours and a characteristic period of Harima-nada is about 60 minutes. The tsunami continued to be resonated for more than 20 hours in the Seto Inland Sea.

Dispersion-Correction Finite Difference Model for Simulation of Transoceanic Tsunamis

A finite difference numerical model, which can correctly consider dispersion effect of waves over a slowly varying water depth, is developed for the simulation of tsunami propagation. The present model employs a linear Boussinesq-type wave equation that can be solved more easily than typical Boussinesq equations. In the present model numerical dispersion is minimized by controlling the dispersion-correction parameter determined by the time step, grid size and local water depth. In order to examine the applicability of the present model to dispersive waves, the propagation of tsunamis is simulated for an initial water surface displacement of Gaussian shape for the cases of several constant water depths and a submerged circular shoal. The numerical results are compared with analytical solutions or numerical solutions of linearized Boussinesq equations. The comparisons show that satisfactory agreement is obtained.

Numerical and Experimental Study on Drift due to Tsunami for Several Drifting Bodies

In order to predict the behavior of floating body under tsunami flood appropriately, it is significant to evaluate the drag force exerted on the float shape when reproducing the dynamics with drift. So, we prepared the drift simulation model based on the Distinct Element Method (DEM). In the simulation, every flotsam shape was expressed by an assembly of individual sphere elements and current velocity field generated by tsunami was given from the result of the tsunami propagation simulation computed in advance. This paper shows experimental results of car's drag force coefficient as a function of every current angle. And we report the application of the drift simulation method by comparing the drift motion from the experiment in a 2-dimensional plane water tank with that of the simulation result.

浮体特性を考慮した漂流シミュレーションの適用性に関する研究

In order to predict the behavior of floating body under tsunami flood appropriately, numerical simulation is effective to reproduce the dynamics with drift. As analyzing the movement of flotsam, it is significant to evaluate the drag force exerted on the float shape.We prepared the drift simulation model based on the Distinct Element Method (DEM). In the simulation, every flotsam shape was expressed by an assembly of individual sphere elements and current velocity field generated by tsunami was given from the result of the tsunami propagation simulation computed in advanceThis paper shows experimental results of container's drag force coefficient as a function of every current angle. And we refer the application of a drift simulation method considering the drag force by comparing the drift motion obtained from the experiment in a 2-dimensional plane water tank with that of the simulation result for above-mentioned float model.

Tsunamis in the Black Sea: Comparison of the historical, instrumental, and numerical data

The tsunami hazard in the Black Sea is discussed by comparing historical, instrumental data and numerical results. There are 22 tsunami events in the Black Sea documented since the first century, and nine of them have occurred in twentieth century. The numerical simulations of tsunami propagation for the 1966 and 1939 events are performed by using the framework of the shallow‐water theory. The instrumental data from tide gauge records are used to compare and validate the simulation results and estimate the wave motion at other locations where the instrumental data are unavailable. The distribution of maximum positive tsunami amplitudes along the north and south coasts are obtained for each event. The arrival time, tsunami amplitudes, and directivity of tsunamis in the Black Sea are studied. The probable source and target areas of tsunamis are discussed.

Re-examination of the Source Mechanism of the 1998 Papua New Guinea Earthquake and Tsunami

Simulation of tsunami propagation and runup of the 1998 Papua New Guinea (PNG) earthquake tsunami using the detailed bathymetry measured by JAMSTEC and adding bathymetric data at depths less than 60 m is carried out, reproducing the tsunami energy focus into Warapu and Arop along the Sissano Lagoon. However, the computed runup heights in the lagoon are still lower than those measured. Even if the error in estimating the fault parameters is taken into consideration, computational results are similar. Analysis by the wave ray method using several scenarios of the source size of the tsunami and location by the wave ray method suggests that a source characterized by small size in water 1,000-m deep approximately 25 km offshore the lagoon, best fits the arrival determined from the interviews with eyewitnesses. A two-layer numerical model simulating the interaction of the tsunami with a landslide is employed to study the behavior of a landslide-generated tsunami with different size sand depths of the initial slide just outside the lagoon. A landslide model with a volume of 4-8 x 109 m3 is selected as the best in order to reproduce the distribution of the measured tsunami runup in the lagoon. The simulation of a tsunami generated in two stages, fault and landslide, could show good agreement with the runup heights and distribution of the arrival time, but a time gap of around 10 minutes remains, suggesting that a tsunami generated by the mainshock at 6:49 PM local time is too small for people to notice, and the following tsunami triggered by landslide or mass movement near the lagoon about ten minutes after the mainshock attacked the coast and caused the huge damage.

Development of a 3D numerical wave tank for modeling tsunami generation by underwater landslides

A three-dimensional (3D) numerical wave tank (NWT) solving fully nonlinear potential flow theory, with a higher-order boundary element method (BEM), is modified to simulate tsunami generation by underwater landslides. New features are added to the NWT to model underwater landslide geometry and motion and specify corresponding boundary conditions in the BEM model. In particular, a new snake absorbing piston boundary condition is implemented to remove reflection from the onshore and offshore boundaries of the NWT. Model results are favorably compared to recent laboratory experiments. Sensitivity analyses of numerical results to the width and length of the discretization are conducted, to determine optimal numerical parameters. The effect of landslide width on tsunami generated is estimated. Results show that the two-dimensional approximation is applicable when the ratio of landslide width over landslide length is greater than 2. Numerical accuracy is examined and found to be excellent in all cases.

Far‐field simulation of tsunami propagation in the Pacific Ocean: Impact on the Marquesas Islands (French Polynesia)

The islands in the Marquesas archipelago are most exposed to far‐field tsunamis in French Polynesia. Four recent earthquakes located at the Pacific rim (Kurile 1994, Chile 1995, Mexico 1995 and Peru 1996 earthquakes) generated trans‐Pacific tsunamis and caused contrasting inundations in several inhabited Marquesian bays. The aim of this study is to better understand the amplification phenomena observed in the Marquesas Islands and to improve the risk assessment. We present here numerical simulations of these four tsunamis by means of a finite difference model solving the equations of tsunami propagation at different scales. The water heights computed in the bays are in excellent agreement with the available observations and thus validate our numerical method. These numerical results allow us to determine (1) which propagation azimuths are dangerous for the whole Marquesas archipelago and (2) the behavior of each studied bay (amplitude, frequency) in response to tsunami waves. We observe that the seismogenic subduction zone along South America is likely to define one of the most dangerous tsunami generation areas for the Marquesas archipelago, owing to the source geometries and to the trapping of the tsunami energy by bathymetric features in the southern Pacific Ocean (fracture zones, seamount chains).

Modeling tsunamis from earthquake sources near Gorringe Bank southwest of Portugal

The Azores‐Gibraltar fracture zone with the huge bathymetric reliefs in the area southwest of Portugal is believed to have been the source of large historic tsunami events. This report describes simulations of tsunami generation and propagation from sources near the Gorringe Bank. The well‐documented 1969 tsunami event is examined both with a ray‐tracing technique and with finite difference models based on various shallow water equations. Both methods show that the most likely source location is southeast of the Gorringe Bank near the epicenter location determined from seismic data. The tsunami source is calculated by formulas given by Okada [1985] for surface deformation of an elastic half‐space caused by faulting. Observed wave amplitude and travel time and values computed from an initial wave field according to Okada [1985] formulas show acceptable agreement for most stations along the coast of Portugal and Spain. However, in order to explain a large primary wave with downward displacement observed on the coast of Morocco, an alternative source model with a larger area of downward displacement has been introduced. This also leads to a better overall fit with observed travel time. Implications for disastrous events, as the one in 1755, are also discussed. Linear hydrostatic shallow water models are used for most of the simulations, but the importance of nonlinearity and dispersion is examined with the Boussinesq equations. The sensitivity of the solution to changes in the location and the strength of the source is discussed, and a series of grid refinement studies are performed in order to assess the accuracy of the simulations.

Numerical Simulation of 1993 Southwest Hokkaido Earthquake Tsunami around Okushiri Island

This paper reports a numerical simulation of tsunami propagation for the 1993 Southwest Hokkaido earthquake tsunami. The model is based on the Boussinesq equation, which includes the effects of frequency dispersion. Energy dissipation due to breaking at the tsunami wave front is modeled. The validity of the model was tested with the existing laboratory data of dispersive wave trains breaking on a slope. The model was then applied to the simulation of the 1993 Southwest Hokkaido earthquake tsunami around the southern part of Okushiri Island. Comparison with the physical model demonstrates that it is the dispersion of the wave front which caused focusing of the wave energy at the narrow region on the lee side of the island, consequently increasing the tsunami height.

Three-Dimensional Modeling of Tsunami Generation Due to a Submarine Mudslide

Abstract Submarine landslides are a common cause of tsunamis in coastal and estuarine areas. To study this phenomenon, a numerical model is developed to simulate tsunami generation due to a viscous mudslide on a gentle uniform slope. A formulation of the dynamics of the problem is presented, where the mudslide is treated as an incompressible three-dimensional viscous flow. Seawater is treated as an inviscid fluid, and the water motion is assumed irrotational. The long-wave approximation is adopted for both water waves and the mudslide. The resulting differential equations are solved by a finite-difference method. The focus of this paper is to examine the effects of the longitudinal spreading as well as the transversal spreading of the slide upon surface wave generation, and the spreading of water waves sideways. Three-dimensional pictures are presented for successive profiles of the mud surface, the horizontal velocities of the mudslide, the evolution of the surface elevations, and the velocities of the w...