Specific Features of the Propagation of Tsunamis in the Northwest Part of the Black Sea

We perform the numerical analysis of the propagation of tsunamis in the Black Sea from the zones of seismic generation located to the south of the Crimea and in the northwest part of the sea. It is shown that the tsunamis induced by earthquakes in the Crimean seismic zone are entrapped by the nearest part of the shelf and do not result in noticeable oscillations of level in the northwest part of the sea. This enables us to explain the absence of manifestations of tsunamis in 1927, 1939, and 1966 near Odessa. The tsunami waves generated by earthquakes in the northwest part of the sea are characterized by the directivity of their propagation. The wave height is maximum in the areas corresponding to the north and east directions of propagation. Hence, the north coast of the sea and the Kalamit Bay (Crimean Peninsula) are characterized by elevated tsunami hazard for earthquakes occurring in the northwest part of the Black Sea. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 46–53, November–December, 2005.     

Numerical modeling of the propagation and strengthening of tsunami waves near the Crimean Peninsula and the Northeast Coast of the Black Sea

The linear model of long waves is used for the evaluation of the parameters of tsunami waves along the South Coast of Crimea, in the near-Kerch zone, and near the northeast coast of the Black Sea. Our numerical investigations are carried out for 24 probable locations of the elliptic zones of tsunami generation over the continental slope of the basin. The amplitude characteristics of tsunamis are computed for 27 sites of the Black-Sea coast. It is shown that significant strengthening of tsunami waves is possible in the course of their propagation toward the coast. The highest waves are formed at the sites of the coast closest to the seismic source. The dependence of the intensity of tsunami waves along the Black-Sea coast on the location of the seismic source and its magnitude is analyzed.     

Assessment of tsunami hazard for coastal areas of Shandong Province,China

Shandong province is located on the east coast of China and has a coastline of about 3100 km. There are only a few tsunami events recorded in the history of Shandong Province, but the tsunami hazard assessment is still necessary as the rapid economic development and increasing population of this area. The objective of this study was to evaluate the potential danger posed by tsunamis for Shandong Province. The numerical simulation method was adopted to assess the tsunami hazard for coastal areas of Shandong Province. The Cornell multi-grid coupled tsunami numerical model (COMCOT) was used and its efficacy was verified by comparison with three historical tsunami events. The simulated maximum tsunami wave height agreed well with the observational data. Based on previous studies and statistical analyses, multiple earthquake scenarios in eight seismic zones were designed, the magnitudes of which were set as the potential maximum values. Then, the tsunamis they induced were simulated using the COMCOT model to investigate their impact on the coastal areas of Shandong Province. The numerical results showed that the maximum tsunami wave height, which was caused by the earthquake scenario located in the sea area of the Mariana Islands, could reach up to 1.39 m off the eastern coast of Weihai city. The tsunamis from the seismic zones of the Bohai Sea, Okinawa Trough, and Manila Trench could also reach heights of >1 m in some areas, meaning that earthquakes in these zones should not be ignored. The inundation hazard was distributed primarily in some northern coastal areas near Yantai and southeastern coastal areas of Shandong Peninsula. When considering both the magnitude and arrival time of tsunamis, it is suggested that greater attention be paid to earthquakes that occur in the Bohai Sea. In conclusion, the tsunami hazard facing the coastal area of Shandong Province is not very serious; however, disasters could occur if such events coincided with spring tides or other extreme oceanic conditions. The results of this study will be useful for the design of coastal engineering projects and the establishment of a tsunami warning system for Shandong Province.     

Correlation between the intensity of tsunami in the Black Sea and the magnitude of underwater earthquakes

We perform the analysis of tsunami waves in the shelf zone of the Crimean peninsula generated by underwater earthquakes whose epicentres are located near the lower boundary of the continental slope. For this purpose, we use a one-dimensional nonlinear dissipative numerical model of long waves. The investigated distributions of the depth of the basin correspond to four points of the south coast of the Crimean peninsula. We use the empirical dependences of parameters of the sources of tsunami waves on the magnitude of the earthquake obtained earlier for the Pacific Ocean. It is shown that the height, vertical climb, and duration of tsunami waves increase with the magnitude of the earthquake. For equal magnitudes of the earthquake, the highest tsunamis on the south coast of the Crimea are observed between Alushta and Yalta. We also deduced a generalized regression dependence of the height of tsunami waves near the coast on the magnitude of the earthquake. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

Numerical analysis of the propagation and amplification of tsunami waves of seismic generation in the Sea of Azov

The numerical analysis of the evolution of tsunamis is performed for the Sea of Azov. Our calculations are carried out on a grid with steps of 500 m, as applied to seaquakes with magnitudes within the range 6–7 for 18 circular zones of generation covering almost the entire water area of the sea. It is shown that the oscillations of the sea level in the form of cellular waves are formed as a result of the wave reflections from the coasts. Small areas of the elevated activity of waves are formed in the zones of irregularity of the coastline on the north coast of the sea and in the zones of shoals in the southeast part of the basin. On the basis of the determined values of extreme elevations and lowerings of the sea level, we can make a conclusion that the tsunami hazard is quite low for the coast of the Sea of Azov.     

The Kuril Earthquakes and tsunamis of November 15, 2006, and January 13, 2007: Observations,analysis, and numerical modeling

Major earthquakes occurred in the region of the Central Kuril Islands on November 15, 2006 (M _w = 8.3) and January 13, 2007 (M _w = 8.1). These earthquakes generated strong tsunamis recorded throughout the entire Pacific Ocean. The first was the strongest trans-Pacific tsunami of the past 42 years (since the Alaska tsunami in 1964). The high probability of a strong earthquake (M _w ≥ 8.5) and associated destructive tsunami occurring in this region was predicted earlier. The most probable earthquake source region was investigated and possible scenarios for the tsunami generation were modeled. Investigations of the events that occurred on November 15, 2006, and January 13, 2007, enabled us to estimate the validity of the forecast and compare the parameters of the forecasted and observed earthquakes and tsunamis. In this paper, we discuss the concept of “seismic gaps,” which formed the basis for the forecast of these events, and put forward further assumptions about the expected seismic activity in the region. We investigate the efficiency of the tsunami warning services and estimate the statistical parameters for the observed tsunami waves that struck the Far Eastern coast of Russia and Northern Japan. The propagation and transformation of the 2006 and 2007 tsunamis are studied using numerical hydrodynamic modeling. The spatial characteristics of the two events are compared.     

Worst scenarios of tsunami effects along the Mediterranean coast of Egypt

Scenarios of tsunami effects represent a very useful technique for the definition and evaluation of tsunami hazard and risk for the Egyptian coast. This paper is an attempt to develop different worst scenarios of tsunamigenesis toward the Egyptian Coast for five segment localities along three different sub-regions (Hellenic Arc, Cyprean Arc and Levantine Coast) in the eastern Mediterranean Sea. These segments are the southwest Hellenic Arc, southeast Hellenic Arc, northeast Hellenic Arc, west of Cyprean Arc and Levantine. For each of them, the scenario takes into account a seismic fault capable of generating an earthquake with magnitude equal to or larger than the highest magnitude registered in that region in historical times. Then the ensuing tsunamis are simulated numerically, highlighting the basic features of the wave propagation and roughly identifying the coastal sectors that are expected to suffer the heaviest tsunami effects. The output data indicated that the first wave of tsunamis from different segments attacked the nearest reference localities (city located nearest each segment) along the Egyptian shore between 28 and 50 min after an earthquake. Tsunamis from these earthquake scenarios produced maximum run-up heights ranging from 1.7 to 9.4 m at the shore. A Beirut Thrust scenario (Levantine segment) included the fact that only a small portion of the fault extended out into the sea, leading to a small effective tsunami source area. In contrast, the southwest Hellenic Arc segment (as in the A.D. 365 earthquake) has high displacement (15 m) and a long extensional fault, forming a highly effective tsunami source area.     

Strongest tsunamis in the World Ocean and the problem of marine coastal security

We consider the problems of assessing tsunami danger for sea coasts taking into account the risk of the strongest tsunamis of seismic origin. We identify a class of particularly dangerous transoceanic events characterized by extremely high runups (up to 40–50 m) at extended coastal areas (up to 500–1000 km). In most cases these transoceanic tsunamis are caused by underwater mega-earthquakes with a magnitude of 9.0 or more occurring with a period between 200–300 and 1000–1200 years in some areas of subduction zones. The possibility of these earthquakes in subduction zones directly threatening a given coast should be taken into account in creating maps of tsunami zoning of any scale.     

Numerical simulation of the action of distant tsunamis on the Russian Far East coast

Results of a numerical simulation of the action of distant tsunamis on the coast of the Russian Far East are presented. It is shown that waves generated by focuses of the strongest M9 earthquakes in the region of South Chilean coast, as well as in the region of Papua New Guinea and Solomon Islands, are most dangerous for this coast. Other tsunamigenic zones of the Pacific Ocean, by virtue of their geographical position, orientation of focuses, and absence of pronounced channels (submarine ridges) along paths of tsunami propagation are not dangerous for it even at a limit magnitude of submarine subduction earthquakes. The simulation results are compared with historical data about manifestations of distant tsunamis on the Russian Far East coast.     

Tsunamis in the central part of the Caspian Sea

This paper describes the geotectonics of the Caspian Sea basin and the seismicity of its central part. The seismicity analysis enables us to identify the most probable zones of tsunami generation. We also present a brief review of the historical records of tsunamis in the Caspian Sea. In order to estimate the tsunami risk, we used the method of numerical hydrodynamic simulation while taking into account the real topography of the Caspian Sea. The computation of the wave field for the possible tsunamis occurring in the central part of the Caspian Sea allowed us to estimate the maximum expected heights of the waves along the coast of the CIS countries (Russia, Azerbaijan, Kazakhstan, and Turkmenistan). On the basis of the earthquake statistics in the region and the results of numerical experiments, we show that the extreme wave heights can reach 10 m at certain parts of the coast. Such extreme events correspond to extended (up to 200 km) seismic sources with M _S ～ 8 and a recurrence period of T ≈ 1600 years. The tsunami wave heights are expected to be as high as 3 m for sources of lesser extent (<50 km) with earthquake magnitudes of M _S ～ 7 and a recurrence period of 200 years.     

Modelling of underwater seismic centres and the generation and transformation of tsunami waves in seismic areas

The mechanism of underwater earthquakes and tsunami wave generation in the Azov Sea-Black Sea region is studied, and theoretical principles of selecting simulation models are elaborated. In this connection, the geophysical data on the distribution, intensity and mechanisms of underwater seismic zones that may give rise to catastrophic disturbances of the marine environment are summarized and categorized, specifically, those that give rise to tsunamis. This makes possible the development and updating of mathematical models for the generation of seismic and surface gravity waves, considering geological heterogeneities, bottom irregularities, bottom sediments, etc. Translated by Vladimir A. Puchkin.     

Scenarios of tsunami amplitudes in the north eastern coast of Sea of Marmara generated by submarine mass failure

In this paper the tsunamis resulting from a submarine mass failure such as slides and slumps triggered by earthquakes or other environmental effects, which is settled at the bottom of the north eastern Sea of Marmara are examined in one sample region. As the solution method, one hybrid method is developed. The main objective of this method is to combine an analytical solution presenting near-field tsunami amplitudes above the submarine mass failure with a numerical solution indicating the tsunami amplitudes in the coastal regions. For this purpose, one common linear boundary between analytical and numerical solution domains is defined. Movements of Submarine Mass Failures (SMF) are modeled using one simple kinematics source model and the amplitudes of the tsunamis at the region that are closer to the landslide are computed by using the analytical method. SMF is modeled approximately from the bottom geometry, and an average depth is used. Scenarios of SMF are established depending on the velocities and thicknesses of the failure, and near-field tsunami amplitudes are obtained in the open sea during the source time. After the source times, the solutions are found in the numerical region using TELEMAC-2D software system with the mentioned boundary above. In this boundary, the output of the analytical solutions is taken as the boundary conditions or the disturbances for the numerical method. With these disturbances, the numerical method is performed and the amplitudes are calculated in the coastal area. The generation, propagation and coastal amplifications of the tsunamis are illustrated at some certain points and regions both in the open sea and near the coast line. The results have been visualized and discussed.     

An investigation of tsunami source mechanism off the coast of central Peru

The source mechanism of the tsunami generated by the earthquake of 17 October, 1966 off the coast of central Peru was inferred by studying the seismic and oceanic phenomena associated with this event. The seismic mechanism was deduced from geologic structure, seismic intensities, energy releases, spatial distribution of aftershocks, and fault-plane solutions. Using this information and empirical relationships of seismic parameters, the fault length, azimuthal orientation of the tsunamigenic area, and initial tsunami height, were obtained. From the tsunami arrival times at selected stations and from a reverse wave-refraction technique, the limits of the tsunami-generating area were estimated. Using these source dimensions, an estimate of the tsunami energy was obtained. The spatial distribution of aftershocks associated with the main earthquake and the earthquake strain-release pattern correlated well with known seismotectonic trends and the seismic-velocity structure anomalies which are characteristic of thrust fault systems at continent-ocean boundaries. The investigation revealed that the tsunamigenic area was on the continental shelf off Peru, northwest of Lima, in the western part of an active seismic belt between the Andean Mountain block and the Peru-Chile trench. This area is considered to be one of three distinct seismic zones in the Peruvian upper mantle and has been responsible for a number of tsunamigenic earthquakes within recorded history. The aftershock distribution and strain-release patterns suggest that the earthquake fault was a seaward extension of a fault system which has a pronounced surface expression in the Tertiary formations of the area near Ancon, Peru. The limits of the tectonic displacements and the tsunami-generating area were determined by a reverse wave-refraction method, refracting waves from Chimbote, Callao-Lima, San Juan, and Honolulu. The investigation revealed that the tsunami was generated by displacements of crustal blocks with a total area of 13,000 sq. km. Seismic and water motion data indicated that the uplifted portion of the crustal block was on the continental side of the rift. The energy of the main earthquake was estimated to be 1.122·10²³ ergs. The energy of the aftershocks was estimated to be 2.357·10²⁰ ergs. The tsunami energy was calculated to be 6.8·10¹⁹ ergs, or $\text{1}\text{1,650}$ of the earthquake energy.     

浙江沿海潜在区域地震海啸风险分析

采用COMCOT海啸模型建立三重网格模型模拟了2011年3月11日日本东北部9.0级地震引发的海啸发生、发展以及在我国东南沿海传播过程。震源附近浮标站以及浙江沿海的潮位站实测资料验证结果显示,大部分监测站首波到达时间和海啸波的计算值相差在15%以内,表明模型可较好的模拟海啸在计算域内的传播过程。研究表明日本南海海槽、冲绳海槽以及琉球海沟南部是影响浙江沿海主要的区域潜在震源,通过情景计算分别模拟3个潜在震源9.1级、8.0级和8.7级地震引发的海啸对浙江沿海的海啸风险,计算结果表明,海啸波产生后可在3~8h内传至浙江省沿岸,海啸波达1~3m,最大可达4m,此时浙江沿岸面临Ⅲ~Ⅳ级海啸风险,达到淹没至严重淹没等级。     

Scenarios of local tsunamis in the China Seas by Boussinesq model

The Okinawa Trench in the East China Sea and the Manila Trench in the South China Sea are considered to be the regions with high risk of potential tsunamis induced by submarine earthquakes. Tsunami waves will impact the southeast coast of China if tsunamis occur in these areas. In this paper, the horizontal two-dimensional Boussinesq model is used to simulate tsunami generation, propagation, and runnp in a domain with complex geometrical boundaries. The temporary varying bottom boundary condition is adopted to describe the initial tsunami waves motivated by the submarine faults. The Indian Ocean tsunami is simulated by the numerical model as a validation case. The time series of water elevation and runup on the beach are compared with the measured data from field survey. The agreements indicate that the Boussinesq model can be used to simulate tsunamis and predict the waveform and runup. Then, the hypothetical tsunamis in the Okinawa Trench and the Manila Trench are simulated by the numerical model. The arrival time and maximum wave height near coastal cities are predicted by the model. It turns out that the leading depression N-wave occurs when the tsunami propagates in the continental shelf from the Okinawa Trench. The scenarios of the tsunami in the Manila Trench demonstrate significant effects on the coastal area around the South China Sea.     

On the problem of local tsunamis and possibilities of their warning

At present, the problem of predicting tsunamis with source earthquakes near the shoreline remains practically unresolved. It is shown that, in the Pacific region, 87% of tsunamigenous earthquake epicenters are located closer than 100 km to the shoreline and 67% are closer than 50 km. For a more detailed analysis, the area of the Pacific Ocean was divided into ten subregions: Kamchatka, the Kuril Islands, Japan, Indonesia, Australia and Oceania, South and Central America, Alaska, and the Aleutian Islands. Each subregion was analyzed individually. All the earthquakes from 1950 to 2003 with Ms >= 6.0 causing tsunamis with intensities I > 0 were processed. The ITDB/PAC 2004 database was used as the data source. For each subregion, mean and minimal travel times were calculated. The minimal travel times for all the regions except for a single one are less than 10 min. It is shown that, in the near earthquake zone, no tsunami alert based sea-level gauge data is possible. One probable solution could be based on detecting hydroacoustic signals that precede strong earthquakes in the near-shore zone.     

Estimations of the parameters of the flux of sediments near the west coast of the Bakal’skaya Spit under the conditions of heavy storms in 2007

On the basis of the wind-energy method, we estimate the distributions of the parameters of a longshore flux of sediments formed near the west coast of the Bakal’skaya Spit (in the northwest part of the Crimea) under the conditions of heavy storms whose action caused a significant erosion of the west coast of the spit and retreat of the coastline in January and November 2007. The calculations are carried out by using the actual directions and velocities of the winds recorded in the investigated region. We analyze the trends of changes in the formation of the coastal zone caused by the nonuniform distribution of the intensity of longshore transportation of sediments. In analyzing the causes of formation of gullies in the barrier of the Bakal’skoe Lake and in the narrow distal part of the body of the spit, we make an attempt of interpretation of the quantities characterizing the force of the frontal action of waves. The obtained numerical results are confirmed by the data of field observations.     

Characterization of earthquake sources in the Gulf of Alaska

Abstract

The characterization of earthquake sources in the Gulf of Alaska and the relative significance of earthquake sources for establishing seismic design inputs at a typical site for engineering purposes are discussed. Earthquake sources in the complex tectonic environment can be divided into two groups: (a) a subduction zone that underlies the entire region (maximum magnitude M = 8.5); and (b) individual thrust and strike‐slip faults associated with the plate motions (maximum magnitude M = 6 to 7.5). The sources of either group and individual earthquake events can be represented as planar surfaces for consistency with the physical process and a mathematically tractable computational scheme.

Although the area is very active seismically, the degree of activity of individual sources varies significantly. Therefore, even for sources with the same maximum earthquakes, different magnitudes may apply for a selected design return period. The area is considered to be a “seismic gap.”; No great earthquakes have occurred in nearly 80 years. Estimates based on a temporally varying seismic function such as the semi‐Markov model indicate that the probability of occurrence of a great earthquake in the near future is significantly higher than the average probability inferred from a statistical analysis of historical seismicity data of the entire region.

Separate attenuation relationships should be used for calculating ground motions due to earthquakes on the dipping subduction zone in the northern portion of the gulf. The dominant earthquake source for almost the entire Gulf of Alaska region is the subduction zone that contributes over 80 percent of the seismic exposure at a typical site. The dominant magnitude range is M_s = 6.5 to 7.5. “Gap filling”; earthquakes (M_s = 7.5 to 8.25) contribute a little over a third of the seismic exposure at a typical site. Deterministic assessments of ground motion values using the maximum earthquake on the subduction zone at the closest distance yield values significantly higher than those calculated for even 500‐year return periods. Estimated 100‐year return period accelerations in the area range from 180 to 340 cm/sec².     

Statistical characteristics and mechanisms of mesoscale eddies in the North Indian Ocean

The statistical characteristics and mechanisms of mesoscale eddies in the North Indian Ocean are investigated by adopting multi-sensor satellite data from 1993 to 2019. In the Arabian Sea(AS), seasonal variation of eddy characteristics is remarkable, while the intraseasonal variability caused by planetary waves is crucial in the Bay of Bengal(BOB). Seasonal variation of the eddy kinetic energy(EKE) is distinct along the west boundary of AS,especially in the Somali Current region. In the BOB, lar...