Generation of tsunamis by a slowly spreading uplift of the sea floor (original) (raw)
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A note on tsunami amplitudes above submarine slides and slumps
Soil Dynamics and Earthquake Engineering, 2002
Tsunami generated by submarine slumps and slides are investigated in the near-®eld, using simple source models, which consider the effects of source ®niteness and directivity. Five simple two-dimensional kinematic models of submarine slumps and slides are described mathematically as combinations of spreading constant or slopping uplift functions. Tsunami waveforms for these models are computed using linearized shallow water theory for constant water depth and transform method of solution (Laplace in time and Fourier in space). Results for tsunami waveforms and tsunami peak amplitudes are presented for selected model parameters, for a time window of the order of the source duration.
Seismically generated tsunamis
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2012
People around the world know more about tsunamis than they did 10 years ago, primarily because of two events: a tsunami on 26 December 2004 that killed more than 200 000 people around the shores of the Indian Ocean; and an earthquake and tsunami off the coast of Japan on 11 March 2011 that killed nearly 15 000 more and triggered a nuclear accident, with consequences that are still unfolding. This paper has three objectives: (i) to summarize our current knowledge of the dynamics of tsunamis; (ii) to describe how that knowledge is now being used to forecast tsunamis; and (iii) to suggest some policy changes that might protect people better from the dangers of future tsunamis.
Essoar, 2021
The repetitive narrative that, "Tsunami waves and receded coastal water initiated by an earthquake are closely related," is analyzed through the sequential events that followed the earthquake; a mechanism based on the interaction of receded water with magma is suggested to explain the amplification of Tsunami wave deep beneath the ocean floor (Fig.1), where earthquake occurred under the seabed's or in coastline; the mechanism explained how the water is amplified into steam in the magma chamber, as its volume increased 1,700 times, the transformed water encompass the tremendous force that uplifted the ocean water endowed it with such destructive force; the mechanism explained characteristics related to Tsunami wave, including relation with earthquake and volcano, receding costal water, the foams, inundation, runup, the nature of the great force of Tsunami, ideas to calculate the magnitude of Tsunami force and energy, volume of receded water, volume of tsunami wave, the repetition of its wave; these and related issues are stated; the idea is derived based on the continual flow of lava from earth's interior and the existence of magma reservoir bellow earth's surface in places like Yellowstone in USA and hotspot beneath Hawaii, such magma chamber when existed under seabed, if opened by crack during earthquake, can easily lead to an interaction between receded water and the magma, resulted in the suggested mechanism, all is based on logical analyses and deep thinking to attained the Tsunami Mechanism in response to 2004 and 2011 human tragedies; thus understanding this mechanism will help laying measures to counter the phenomenon, which will reflect positively in saving lives and mitigate its destructive force and reduce consequences of its impact on local societies and above all to understand its true mechanism.
A note on differences in tsunami source parameters for submarine slides and earthquakes
Soil Dynamics and Earthquake Engineering, 2002
The nature of tsunami sources is reviewed, including source duration, displacement amplitudes, and areas and volumes of selected past earthquakes, slumps and slides that have or may have generated a tsunami. This review shows that the velocity of spreading of submarine slides and slumps (1±100 m/s) can be comparable to the long wavelength tsunami velocity c T gh p (30±140 m/s for water depth 100 , h , 2000 m). In contrast, typical velocities of spreading dislocations during most earthquakes are one order of magnitude larger (2±3 km/s). Other signi®cant differences between earthquake and slide and slump sources are that the balance of the total uplifted material in the case of slides is essentially zero, while for earthquakes it can be considerable, and that the vertical displacements for slides and slumps, per unit area of their horizontal projection, can be orders of magnitude larger than during earthquakes. This can result in high concentrations of the total change in the potential energy of¯uid, above the source, over much smaller areas than during earthquakes. q
Non-seismic and Complex Source Tsunami: Unseen Hazard
IntechOpen, 2024
Tsunamis, commonly induced by undersea earthquakes, are formidable natural hazards capable of causing widespread devastation. This comprehensive chapter examines the complex dynamics of tsunamis, their generation mechanisms, and their broad-reaching impacts. The multifaceted nature of tsunami triggers, both seismic and non-seismic, is dissected, highlighting the role of undersea earthquakes, landslides, volcanic eruptions, and meteorological events in driving these devastating natural phenomena. The intricate interplay of seismic parameters such as magnitude, depth, and activity type is elaborated, underscored by an insightful case study on the 2011 Tohoku Earthquake and Tsunami. A pivotal part of the discussion lies in the exploration of non-seismic triggers of tsunamis, an area often overshadowed in tsunami studies. The impact of landslide-induced and volcanically triggered tsunamis is considered alongside the contentious topic of meteorologically influenced tsunami events. Delving further into the genesis of tsunamis, the chapter explores the influences of bathymetry and tectonic structures, particularly in the context of non-seismic tsunami generation. The chapter serves as a beacon for continuous research and predictive modeling in the field of tsunami studies, emphasizing the necessity for societal preparedness and strategic risk mitigation against these potent natural disasters.
Soil Dynamics and Earthquake Engineering, 2003
Tsunami created by spreading submarine slides and slumps with spatially variable final uplift are investigated in the near-field using a kinematic model. It is shown that for velocities of spreading comparable to and smaller than the long period tsunami velocity c T ¼ ffiffiffi gh p (g is the acceleration due to gravity and h is the ocean depth), the models with spatially uniform final uplift of the accumulation and depletion zones provide good approximation for the tsunami amplitudes in the near-field. For spreading velocities 2 -5 times greater than c T ; and for applications that use wavelengths of the order of the source dimensions, the spatial variability of the final uplift has to be considered in estimation of the high-frequency tsunami amplitudes in the near-field. q
Tanioka and Satake : Tsunami Generation by Horizontal Movement 863
2008
Tsunami generation by an earthquake is generally modeled by water surface displacement identical to the vertical deformation of ocean bottom due to faulting. The effect of horizontal deformation is usually neglected. However, when the tsunami source is on a steep slope and the horizontal displacement is large relative to the vertical displacement, the effect becomes significant. We show this for two recent earthquakes which generated much larger tsunamis than expected from seismic waves. In the case of the 1994 June 2 Java, Indonesia, earthquake, the focal mechanism was a very shallow dipping thrust and the source was near a very steep trench slope. In the case of the 1994 Nov. 14 Mindoro, Philippines, earthquake, strike-slip faulting extended from ocean to land perpendicular to the coast line. In both cases, we found that the horizontal motion of slope had an important contribution to the tsunami generation.
Tsunami generation by horizontal displacement of ocean bottom
Geophysical Research Letters, 1996
Tsunami generation by an earthquake is generally modeled by water surface displacement identical to the vertical deformation of ocean bottom due to faulting. The effect of horizontal deformation is usually neglected. However, when the tsunami source is on a steep slope and the horizontal displacement is large relative to the vertical displacement, the effect becomes significant. We show this for two recent earthquakes which generated much larger tsunamis than expected from seismic waves. In the case of the 1994 June 2 Java,
Tsunami Earthquakes: Slow Thrust-Faulting Events in the Accretionary Wedge
Journal of Geophysical Research, 1992
are classified as tsunami earthquakes based on anomalously large tsunami excitation relative to earthquake magnitude. Long-period surface wave analysis indicates double-couple (faulting) mechanisms for all three events rather than single-force mechanisms indicative of submarine landslides. The earthquakes have shallow depths (< 15 km) and are located near the trench axis and seaward of most other thrust zone events beneath the accretionary prism. Body waveform inversion indicates very shallowly dipping thrust faulting mechanisms for the three events, with dip angles of 6 ø-8 ø. Surface wave spectral amplitudes and deconvolution of SH waveforms suggests anomalously long source durations and large seismic moments relative to M s. Specifically, the 1963 Kurile event (M s 7.2) shows a duration of 85 s and a moment of 6.0 x 10 27 dyn cm (M w 7.8), the 1975 Kurile event (M s 7.0) shows a duration of 60 s and a moment of 2.0 x 10 27 dyn cm (Mw 7.5), and the 1960 Peru event (M s 6.75) shows a time function consisting of four subevents with a total duration of 110-130 s and a seismic moment of 3.4 x 10 27 dyn cm (M w 7.6). Estimated rupture velocities are about 1 km/s or less, but there is no evidence of unusually low stress drops. The August 1, 1968, Philippines event, previously classified as a tsunami earthquake, shows none of the anomalous source properties, and teleseismic tsunami height measurements are sparse; we do not consider this event a tsunami earthquake. Most of the "anomalous" tsunami excitation results from underestimation of earthquake size by M s due to the long source duration; the tsunami heights are not significantly anomalous relative to seismic moment. The slow nature of these events may result from rupture through the sedimentary rock along the basal decollement of the accretionary prism. Standard scaling laws when adjusted for the slow seismic velocity in the source region show an M w -M s relationship similar to that observed for the tsunami earthquakes and predict Ms saturation at about 7.3 rather than 8.0 for typical events. INTRODUCTION Very large earthquakes are generally required to excite a Earthquakes that produce anomalously large tsunamis substantial tsunami [e.g., Ward, 1980], so the occurrence of relative to earthquake magnitude are among the most moderate-magnitude tsunami earthquakes presents a ].ntriguing seismic events. Kanamori [1972] introduced the dilemma. Various investigators have offered different
The deficientTwaves of tsunami earthquakes
Geophysical Journal International, 2003
We develop an algorithm quantifying the energy flux of T phases recorded at island stations following major teleseismic events, which we further scale by the seismic moment M 0 of the earthquake, to define a T-phase efficiency,. We apply this concept to a set of six recognized tsunami earthquakes, which generated tsunamis larger than expected from their conventional seismic waves. Through comparison with nearby reference events the T waves of which were recorded at the same sites, we find that the tsunami earthquakes exhibit a deficiency in ranging from 1.5 to 2.5 orders of magnitude. This result settles a 50 yr old controversy on the possible correlation between T-wave generation and tsunami genesis. The deficient character of the T waves from tsunami earthquakes readily supports the proposed model of an exceedingly slow rupture velocity for this class of events, and the close examination of T wave trains supports the concept of a jerky rupture in at least two cases. The computation of is straightforward in real time, and could become a valuable contribution to real-time tsunami warning in the far field.