ИСТИНА

Traditionally in tsunami simulation the initial water surface elevation in the tsunami source is used as an initial condition. For the calculation of this initial elevation the three component ocean bottom displacement field is used while the effect of bottom topography [1] and the smoothing effect of water layer [2] are taken into account. Theoretical analysis shows that under certain conditions the significant amplification of the tsunami amplitude due to the bottom deformation dynamics could be observed. In particular, the rupture propagation velocity should be comparable to the long waves velocity and the uplifted area should be large enough [3-6]. Not all the real tsunami sources meet the above mentioned conditions, but for some sources these conditions occurred. We present the detailed analysis of such events. Finite Fault products provided by the USGS web site allows us to create two different types of the seafloor displacement fields: the final displacement field and the time-dependent displacement field. We used these two types of the bottom displacement field as an input data for the comparative tsunami simulation, considering passive and active tsunami generation scenarios, respectively [7]. Active generation scenario means that for the tsunami simulation we use the bottom movement as a time-dependent kinematic boundary condition. Passive generation scenario means that we use an initial elevation of the water surface in the tsunami source as an initial condition for simulation. Tsunami simulations were performed with the use of the Combined Potential Tsunami Model (CPTM) [8, 9]. CPTM model solves 3D wave equations for the compressible fluid and allows to dynamically input the bottom movement information on each time step of the simulation. Comparative numerical simulation showed, that the tsunami amplitude amplification takes place during the strong events (for example, 2011/03/11 catastrophic Mw 9.1 Tohoku event or 2006/11/15 Mw 8.3 Kuril Islands event), and also during the tsunami earthquakes (for example, 1992/09/02 Mw 7.7 Nicaragua event). The features of the directivity diagrams of the tsunami energy radiation for different cases will be discussed. References 1. Tanioka Y., Satake K. (1996). Tsunami generation by horizontal displacement of ocean bottom // Geophysical research letters. 23. –№. 8. –P. 861-864. 2. Kajiura K. (1963). The leading wave of a tsunami // Bulletin of the Earthquake Research Institute, University of Tokyo. 41. –№. 3. –P. 535-571. 3. Novikova L. E., Ostrovsky L. A. (1979). Excitation of tsunami waves by a traveling displacement of the ocean bottom // Marine Geodesy, 2(4). –P. 365-380. 4. Nosov M. A. (1996). A comparative study of tsunami excited by piston-type and traveling-wave bottom motion. Volcanology & Seismology. –№ 6. –P. 693-698 5. Nosov M. A. (1998). On the directivity of dispersive tsunami waves excited by piston-type and traveling-wave sea-floor motion // Volcanology & Seismology. –№ 6. –P. 837-844 6. Todorovska M. I., Trifunac M. D. (2001). Generation of tsunamis by a slowly spreading uplift of the sea floor // Soil Dynamics and Earthquake Engineering. 21. –№. 2. –P. 151-167. 7. Kervella Y., Dutykh D., Dias F. (2007). Comparison between three-dimensional linear and nonlinear tsunami generation models // Theoretical and computational fluid dynamics. 21. –№. 4. –P. 245-269. 8. Nosov M. A., Kolesov S. V. (2019). Combined numerical model of tsunami // Mathematical Models and Computer Simulations. 11. –№. 5. –P. 679-689. 9. Sementsov K. A., Nosov M. A., Kolesov S. V., Karpov V. A., Matsumoto H., Kaneda Y. (2019). Free gravity waves in the ocean excited by seismic surface waves: Observations and numerical simulations //Journal of Geophysical Research: Oceans. 124. –№. 11. –P. 8468-8484.