Deformation Anomalies Accompanying Tsunami Origination

Basing on the analysis of data on variations of deformations in the Earth’s crust, which were obtained with a laser strainmeter, we found that deformation anomalies (deformation jumps) occurred at the time of tsunami generation. Deformation jumps recorded by the laser strainmeter were apparently caused by bottom displacements, leading to tsunami formation. According to the data for the many recorded tsunamigenic earthquakes, we calculated the damping ratios of the identified deformation anomalies for three regions of the planet. We proved the obtained experimental results by applying the sine-Gordon equation, the one-kink and two-kink solutions of which allowed us to describe the observed deformation anomalies. We also formulated the direction of a theoretical deformation jump occurrence—a kink (bore)—during an underwater landslide causing a tsunami.

ON GEODYNAMIC CONDITIONS AND UNDERWATER-LANDSLIDE DEFORMATIONS IN THE ULUTAU FORMATION

To understand the features of geodynamics during the accumulation of the systems of geological matter in the Earth's crust at the formation level of the Paleozoic Urals, this paper presents the author's factual materials on structural characteristics of clastic rocks of the flysch sequence of the Ulutau Formation (Middle Devonian Givetian) within the mapping area of the Urtazym zone of the Magnitogorsk Synclinorium. Here, to the west of the village of Tash-Tugay, rhythmites are developed in the lower reaches of the Tanalyk River that show very informative underwater interlayer dislocations: cross-bedding, spherical and folded structures serving as a decisive marker for the synchronism of sedimentation and dislocation. They characterize the deformation period in the tectonic development of the folded region, according to the main points of the thrust-nappe theory of the formation of the Earth's crust and the scientific research area «structural factor in theoretical geology».

Numerical simulation of surface waves in a basin with moving impermeable boundaries

Представлены результаты, связанные с разработкой вычислительного алгоритма для изучения поверхностных волн в областях с подвижными непроницаемыми границами (подвижные боковые стенки бассейна, подвижные фрагменты дна). Алгоритм основан на конечноразностной аппроксимации на подвижных сетках двумерной модели потенциальных течений несжимаемой жидкости со свободной границей. Предложены новые начальные данные для задачи о движении уединенной волны, неотражающие условия, способ задания нулевого итерационного приближения для расчета потенциала скорости и результаты исследования устойчивости численного метода. Показано, что поверхностные волны, вызванные подводным оползнем, существенно влияют на процесс наката на берег одиночной волны и могут увеличить ее максимальный заплеск. In numerical simulation of fluid flows with a free surface, the most difficult problems are those in which not only the free boundary is mobile, but also some other parts of the boundary of the region occupied by the liquid. For example, these are the problems of surface waves caused by underwater and coastal landslides, the generation of waves by wavemakers in laboratory flumes and tanks, the problem of waves runup on the shore, the interaction of waves with moving wave protection walls and problems addressed moving semisubmerged or fully immersed objects. The purpose of this paper is to analyze the properties and evaluate the capabilities of the computational algorithm based on the finitedifference approximation of the equations of potential fluid flows with a free boundary and designed to study surface waves in a confined basin, part of the impermeable boundary of which can be mobile. The algorithm relies on the use of curvilinear grids that adapt to all parts of the boundary, both moving and stationary. New initial data are proposed for the problem of motion of a solitary or a single wave, consistent with the initial data for the shallow water equations of the second longwave approximation. New nonreflecting conditions have been developed that allow waves to be emitted across the boundary of a flow region with very little reflection. A new initial approximation is proposed for the iterative process of calculating the potential of the velocity vector. By using this approach we significantly reduce the number of iterations at each time step. The original stability condition of the linearized difference scheme is derived. The reasons for the appearance of two peaks in the chronograms of pressure when the long waves of large amplitude roll onto a vertical wall are discussed. The capabilities of the numerical algorithm are demonstrated on the problem of generating waves by a moving wall travelling in the initial part of the flume. The results of the calculations well reproduce the experimental data, in particular, the decrease in the length and increase in the amplitude of the wave when it moves towards the shallow part of the flume, as well as the formation of a dispersion tail as the waves reverse motion after reflection from the vertical wall installed at the end of the flume. The developed algorithm was used to study the process of generation for surface waves by an underwater landslide moving along an uneven bottom, and the interaction of these landslide waves with a single surface wave moving towards the shore. It is shown that the surface waves caused by an underwater landslide significantly affect the process of rolling of a single wave on the shore and it could increase its maximum splash.

Momentum Conservative Scheme for Simulating Wave Runup and Underwater Landslide

This paper focuses on the numerical modelling and simulation of tsunami waves triggered by an underwater landslide. The equation of motion for water waves is represented by the Nonlinear Shallow Water Equations (NSWE). Meanwhile, the motion of underwater landslide is modeled by incorporating a term for bottom motion into the NSWE. The model is solved numerically by using a finite volume method with a momentum conservative staggered grid scheme that is proposed by Stelling & Duinmeijer 2003 [12]. Here, we modify the scheme for the implementation of bottom motion. The accuracy of the implementation for representing wave runup and rundown is shown by performing the runup of harmonic wave as proposed by Carrier & Greenspan 1958 [2], and also solitary wave runup of Synolakis, 1986 [14], for both breaking and non-breaking cases. For the underwater landslide, result of the simulation is compared with simulation using the Boundary Integral Equation Model (BIEM) that is performed by Lynett and Liu, 2002 [9].

Solving the Puzzle of the September 2018 Palu, Indonesia, Tsunami Mystery: Clues from the Tsunami Waveform and the Initial Field Survey Data

On September 28, 2018, following a magnitude 7.5 strike-slip fault earthquake, an unexpected tsunami inundated the coast of Palu bay, Sulawesi, Indonesia, causing many casualties and extensive property damage. However, the earthquake’s mechanism rarely generates a destructive tsunami. The tidal record at Pantoloan, located along the coast of Palu bay, indicates that the tsunami arrived 6 min after the earthquake and generated 2 m of receding water. It had a maximum wave height of 2 m and arrived approximately 2 min later. The tsunami had a relatively short period and caused devastation as far inland as 300 m. Additionally, 8 m high watermarks were observed near the coast; the flow depth decreased to 3.5 m inland (Fig. 1). Amateur videos and eyewitness accounts indicate that the tsunami did not enter the bay through its mouth but obliquely from an area inside the bay. Our hypothesis, therefore, is that the killer tsunami was most likely generated by an underwater landslide occurring inside Palu bay. While detailed bathymetric data are still needed to confirm this hypothesis, in this article we provide a preliminary analysis of the available data, supported by the results of a field survey, to strengthen this hypothesis and provide direction for further post-tsunami surveys and analysis.