Submarine Mass Failure Research Articles

Evaluation of tsunami inundation in the plain of Martil (north Morocco): Comparison of four inundation estimation methods

The Alboran Basin may be subject to tsunami hazards. If such an event were to occur, it is expected that the urbanised and densely populated areas of northern Moroccan coastline would be affected. Precise inundation hazard maps are needed for tsunami risk management in this region. In this article, we argue that the diversity of hazard mapping methods ensures the robustness of the scientific knowledge about the exposure of a territory. Hence, the main objective of this study is to analyse the exposure of the plain of Martil (north of Morocco), by using four hazard mapping methods to create inundation maps for two scenarios of tsunamis generated by extreme submarine mass failure (SMF) in the Alboran Sea, of 0.9 ​km3 and 3.8 ​km3 respectively. A digital terrain model of the plain was used to explore four methods of inundation mapping. The static method identified 4.32 ​km2 and 19.83 ​km2 of flooded areas for each scenario using water height values as inundation thresholds. The hybrid and the volumetric methods use the volume of water to determine the inundation extent. For the first scenario, 3.51 ​km2 of the plain were inundated using the hybrid method, and 20.11 ​km2 for the second scenario. The results of the volumetric methods are 2.32 ​km2 and 7.82 ​km2 respectively for the first and second scenario. Finally, the fourth method relies on numerical hydrodynamic modelling of tsunami inundation (Freshkiss3d® code). With this method, 4.55 ​km2 of the plain were flooded in the first scenario, and 24.12 ​km2 for the second. The comparison of the results highlights that the most sensitive areas to tsunami inundation are the lowest topographic ones, being the beaches and the wadis floodplains. This result raises questions on the current coastal development and the preparedness of its population, thus calling for more attention to engage on tsunami risk management related questions.

Global research on submarine landslides, 2001–2020

Submarine landslides, one of the hotspots in marine geoscience research, are one of the most harmful marine geological disasters. To understand the research status and further research directions of submarine landslides, this paper analyzed the global submarine landslide-related work during the period from 2001 to 2020. To achieve this objective, Science Citation Index Expand and the Social Sciences Citation Index, belonging to the WoS Core Collection, were the two bibliographic databases selected as a reference. In this study, we focused on document types, publishing languages, subject categories, journals’ productivity, countries and author, and co-occurrence keywords network. Geoscience multidisciplinary, Geochemistry Geophysics, Oceanography, Environmental Sciences, and Materials Science Multidisciplinary have been the most commonly used science categories in the past two decades. Marine Geology, Marine and Petroleum Geology, Journal of Volcanology, and Geothermal Research are the three most productive journals on submarine landslides. Marine Geology is the most active journal among all the journals. The United States, the United Kingdom, China, Germany, and France are the five most productive countries. At the institutional level, the Centre National De la Recherche Scientifique (France) is the most active institution, followed by the Chinese Academy of Sciences (China) and Helmholtz Association (Germany). Masson DG and Talling PJ from the United Kingdom contribute to the most high-quality submarine landslide-related publications. Analyzing by CiteSpace, the five largest clusters in the submarine landslide field are “gas hydrate,” “turbidity current,” “thin film,” “debris avalanche,” and “submarine canyon.” Active further research directions of submarine landslides are “south china sea,” “slump,” and “submarine mass failure.”

An earthquake-triggered submarine mass failure mechanism for the 1994 Mindoro tsunami in the Philippines: Constraints from numerical modeling and submarine geomorphology

Tsunamis have been known to result from a wide range of phenomena, such as earthquakes, volcanic eruptions, submarine mass failures, and meteorite impacts. Of earthquake-generated tsunamis, those arising from strike-slip mechanisms are less common, with the 1994 Mindoro tsunami in the Philippines among the few known examples. The 1994 Mindoro tsunami followed a Mw 7.1 earthquake along the right-lateral Aglubang River Fault. The tsunami affected the coasts surrounding the Verde Island Passage, one of the Philippines’ insular seas located between the islands of Luzon and Mindoro, and east of the West Philippine Sea margin. A total of 78 lives were lost due to the earthquake and tsunami, with 41 being directly attributed to the tsunami alone. Despite the close spatial and temporal association between the 1994 Mindoro earthquake and tsunami, previous numerical modeling suggests the need for other contributing mechanisms for the 1994 tsunami. In this study, we conducted submarine geomorphological mapping of the South Pass within the Verde Island Passage, with particular focus on identifying possible submarine mass failures. Identification of submarine features were based on Red Relief Image Map (RIMM), Topographic Position Index (topographic position index)-based landform classification, and profile and plan curvatures derived from high-resolution bathymetry data. Among the important submarine features mapped include the San Andres submarine mass failure (SASMF). The San Andres submarine mass failure has an estimated volume of 0.0483 km3 and is located within the Malaylay Submarine Canyon System in the Verde Island Passage, ∼1 km offshore of San Andres in Baco, Oriental Mindoro. We also explored two tsunami models (EQ-only and EQ+SMF) for the 1994 Mindoro tsunami using JAGURS. The source mechanisms for both models included an earthquake component based on the Mw 7.1 earthquake, while the EQ+SMF also included an additional submarine mass failure component based on the mapped San Andres submarine mass failure. Modeled wave heights from the EQ-only model drastically underestimates the observed wave heights for the 1994 Mindoro tsunami. In contrast, the EQ+SMF model tsunami wave height estimates were closer to the observed data. As such, we propose an earthquake-triggered, submarine mass failure source mechanism for the 1994 Mindoro tsunami.

Historical tsunamis of Taiwan in the 18th century: the 1781 Jiateng Harbor flooding and 1782 tsunami event

Abstract. This research aims to study two historical tsunamis that occurred in Taiwan during the 18th century and to reconstruct the incidents. The 1781 Jiateng Harbor flooding, recorded by the Chinese historical document entitled “Taiwan Interview Catalogue” took place on the southwest coast of Taiwan. In contrast, the 1782 tsunami was documented in foreign languages, with uncertainties about the actual time. These two events seem to be close enough in time and location that, to some researchers, they are considered as the same event. Reasoning these historical events requires carefully examining the literature records and performing the scenarios that match the descriptions. The impact intensity analysis (IIA) is employed to locate possible regions of tsunami sources in order to reproduce the events. Numerical simulations based on the Cornell Multi-grid Coupled Tsunami Model (COMCOT) analyze the influence of different types of tsunamis generated by both submarine mass failures and seismic activities. Numerical results indicate that the source of the 1781 Jiateng Harbor flooding is located very possibly on the south-southwestern side of Taiwan. However, simulation results and historical records put the existence of the 1782 tsunami in doubt, and the possibility of storm surges could not be ruled out.

Reciprocal Green's Functions and the Quick Forecast of Storm Surges

AbstractPre‐calculated reciprocal Green's functions are accurate and efficient for forecasting tsunamis generated by either submarine mass failures or submarine earthquakes. In the present study, reciprocal Green's functions are extended to the forecast of storm surges. As the reciprocity between volume flows is not natural, new reciprocity relations are first established and verified. These reciprocal Green's functions, after a convolution with the atmospheric pressure and wind stress, can give the water surface and volume fluxes of the storm surge promptly. Thus, various storm surge scenarios can be considered, and a useful forecast can be devised. Detailed simulations on storm surge inundation can be obtained quickly in a way similar to tsunami inundation.

Recent Developments in Sea-Level Rise and Its Related Geological Disasters Mitigation: A Review

With the rapid development of urbanization around the world, the sea-level-rise problem is gaining more and more attention in the 21st century. Sea-level rise is the result of a combination of climate-related factors, structural factors and human activities. Recent studies related to the contributions of these factors to sea-level rise are reviewed and analyzed in this paper. The results suggest that the melting of glaciers and ice sheets have contributed the most to sea-level rise and will continue to be the dominant factor in sea-level rise for the following decades. As sea-level rise becomes an increasingly serious problem, geological disasters related to sea-level rise are also gaining more attention. To better understand the effect of sea-level rise on geological disasters, relevant issues including storm surges, seawater intrusion, the loss of coastal wetland, seismicity, seismic liquefaction and submarine mass failure are further reviewed and highlighted. In response to the risks of those disasters caused by sea-level rise, some disaster mitigation measures are proposed, and in the end, the quantitative disaster assessment concept based on resilience is introduced to the coastal urban system, to assess its ability to resist and recover from geological disasters due to the sea-level rise.

Response to: Comment on “New simulations and understanding of the 1908 Messina tsunami for a dual seismic and deep submarine mass failure source” by L. Schambach, S.T. Grilli, D.R. Tappin, M.D. Gangemi, G. Barbaro [Marine Geology 421 (2020) 106093

In this response, we address and refute the comments made by Argnani (2021) on our 1908 Messina tsunami paper (Schambach et al., 2020), regarding the poor geological constraints underpinning the numerical tsunami modeling. Earthquake mechanisms can be constructed from ‘geology’, but because ruptures are usually blind, seabed evidence may be absent. Alternatively, with small magnitude earthquakes, such as Messina 1908, the small vertical displacements may not be resolved on seismic or multibeam echosounder bathymetric records, because of the relatively low frequencies of the recording equipment. Hence, for earthquake tsunami, seismological data may be more appropriate as the basis for numerical modeling. With regard to submarine mass failure, when interpreting seismic and bathymetry data, the frequency content should again be carefully considered, because smaller features may not be resolved. Regarding the 1908 tsunami, the Mw 7.1 earthquake magnitude would not be expected to generate the recorded tsunami runups for the 5 sources we modeled, as is proved from our modeling; this would also be the case for the Barreca et al. (2021) source proposed in the discussion. Combined with any of these earthquake sources, the submarine mass failure we identified and mapped, however, in large part does. The evidence most critical to the age dating of our identified SMF, presented as too old in the discussion, is that: (i) it is at the location predicted by the inverse wave ray tracing based on tsunami arrival observations; and (ii) upon forward modeling, this tsunami mechanism generates the onland tsunami record.

Comment on “New simulations and understanding of the 1908 Messina tsunami for a dual seismic and deep submarine mass failure source” by L. Schambach, S.T. Grilli, D.R. Tappin, M.D. Gangemi, G. Barbaro [Marine Geology 421 (2020) 106093

In their paper Schambach et al. (2020) present a dual (seismic and landslide source) modelling of the 1908 Messina tsunami. Their contribution highlights the fact that a multiple source is required to model the 1908 tsunami event. However, both the seismogenic fault and the submarine mass failure adopted by Schambach et al. are geologically poorly constrained. Dual-source modelling can satisfactorily fit to observations but the source components should be based on geological ground. Various authors have explored the contribution of submarine landslides into the 1908 tsunami generation; it could also be of interest, however, to consider the possible tsunamigenic contribution of secondary faults.

Orbital‐ and Millennial‐Scale Changes in Lake‐Levels Facilitate Earthquake‐Triggered Mass Failures in the Dead Sea Basin

AbstractThe possible link between the occurrence of submarine mass failure and climate‐driven factors is highly disputed. This is due largely to the lack of comprehensive records of mass failures in the geologic record for which ages, triggers, and preconditioning factors can be reliably constrained. Such controls would allow accurate testing of cause‐and‐effect relationships. We present a record that comprises 490 earthquake‐triggered mass failure deposits from the Dead Sea depocenter over the past 220 kyr that permits a robust statistical evaluation and correlation with potential preconditioning factors. Our data set reveals that (a) at the orbital‐ and millennial‐scale, variable sedimentation rates are not a preconditioning factor for these mass failure deposits; (b) at the centennial‐to decadal‐scale, earthquake‐triggered mass failures can occur at any lake‐level state; (c) at the orbital‐ and millennial‐scale, the mass failures are more frequent when lake‐levels were high and punctuated by large‐amplitude fluctuations.

Reciprocal Green's functions and the quick forecast of submarine landslide tsunamis

Abstract. Although tsunamis generated by submarine mass failure are not as common as those induced by submarine earthquakes, sometimes the generated tsunamis are higher than a seismic tsunami in the area close to the tsunami source, and the forecast is much more difficult. In the present study, reciprocal Green's functions (RGFs) are proposed as a useful tool in the forecast of submarine landslide tsunamis. The forcing in the continuity equation due to depth change in a landslide is represented by the temporal derivative of the water depth. After a convolution with reciprocal Green's function, the tsunami waveform can be obtained promptly. Thus, various tsunami scenarios can be considered once a submarine landslide happens, and a useful forecast can be formulated. When a submarine landslide occurs, the various possibilities for tsunami generation can be analyzed and a useful forecast can be devised.

Multisource Bayesian Probabilistic Tsunami Hazard Analysis for the Gulf of Naples (Italy)

AbstractA methodology for a comprehensive probabilistic tsunami hazard analysis is presented for the major sources of tsunamis (seismic events, landslides, and volcanic activity) and preliminarily applied in the Gulf of Naples (Italy). The methodology uses both a modular procedure to evaluate the tsunami hazard and a Bayesian analysis to include the historical information of the past tsunami events. In the the submarine earthquakes and the submarine mass failures are initially identified in a gridded domain and defined by a set of parameters, producing the sea floor deformations and the corresponding initial tsunami waves. Differently volcanic tsunamis generate sea surface waves caused by pyroclastic density currents from Somma‐Vesuvius. In the the tsunami waves are simulated and propagated in the deep sea by a numerical model that solves the shallow water equations. In the the tsunami wave heights are estimated at the coast using the 's amplification law. The selected tsunami intensity is the wave height. In the the probabilistic tsunami analysis computes the long‐term comprehensive Bayesian probabilistic tsunami hazard analysis. In the prior analysis the probabilities from the scenarios in which the tsunami parameter overcomes the selected threshold levels are combined with the spatial, temporal, and frequency‐size probabilities of occurrence of the tsunamigenic sources. The probability density functions are integrated with the derived from the historical information based on past tsunami data. The probability density functions are evaluated to produce the hazard curves in selected sites of the Gulf of Naples.

New simulations and understanding of the 1908 Messina tsunami for a dual seismic and deep submarine mass failure source

Over 100 years after the event, the mechanism of the 1908 Messina tsunami remains unresolved. The up to 12 m runups observed along the coasts of Sicily and Calabria cannot be explained by the coseismic tsunami, so recent studies have proposed a dual earthquake/submarine mass failure (SMF) mechanism. Here we propose a new dual source and use it to simulate tsunami generation with a three-dimensional non-hydrostatic model, coupled to a two-dimensional fully nonlinear and dispersive model, to simulate tsunami propagation to shore. We first reanalyze observations of tsunami arrival times from eyewitnesses acquired shortly after the 1908 event, and a tsunami record at a tide gauge in Malta. Similar to earlier work, this data is used to locate the likeliest tsunami source area by inverse wave ray tracing, but accounting for frequency dispersion effects on wave celerity, uncertainty in reported arrival times, and a time delay between the EQ and SMF triggering. Analyzing the seafloor morphology in this area, we identify a new SMF at the foot of the Fiumefreddo Valley, northeast of Mount Etna. The general location is consistent with earlier studies, however our SMF is much smaller (~2 km3) than, e.g., that of Billi et al. (2008) and is a fairly rigid-block-slump, rather than a translational SMF. We model the block motion and simulate tsunami generation from a dual EQ/SMF source, and its propagation to shore, in higher resolution grids and based on more accurate bathymetry and topography than in earlier work. Runups and travel times agree well with observations, except for runups on either side of the Messina Straits north of the SMF, which are still underpredicted. In the far field, simulations reproduce well the arrival time and initial wave amplitudes at the Malta tide gauge. Our newly parameterized SMF and modeling improve tsunami runups simulated near the SMF location and south of it. However, as with all previous modeling of this event, additional sources are required to explain runups in the northern Messina Straits, which we suggest might be smaller and shallower SMFs located in this area. These will be considered in future work.

Internal tsunami waves transport sediment released by underwater landslides

Accelerated by gravity, submarine landslides transfer energy to the marine environment, most notably leading to catastrophic tsunamis. While tsunamis are thought to use less than 15% of the total energy released by landslides, little is known about subsurface processes comprising the rest of their energy budgets. Here, we analyze the first set of observations depicting a lake’s interior response to underwater landslides and find that sediment transport is modulated by baroclinic waves that propagate along vertical gradients in temperature and sediment concentration. When traveling along a shallow thermocline, these waves can reach past topographic features that bound turbidity currents and thus expand the influence area of underwater landslides. With order of magnitude calculations, we estimate that observed thermocline internal waves received roughly 0.7% of available landslide energy and infer their contribution to homogenize the lake’s thermodynamical properties by means of turbulent mixing. Lastly, we show that landslides in our data set modified the lake’s intrinsic dynamical modes and thus had a permanent impact on its circulation. This suggests that measurements of subsurface wave propagation are sufficient to diagnose bathymetric transformations. Our experiment constitutes the first direct observation of both internal tsunami waves and turbidity current reflection. Moreover, it demonstrates that background density stratification has a significant effect on the transport of sediment after submarine landslides and provides a valuable reference for numerical models that simulate submarine mass failures.

Probabilistic Landslide-Generated Tsunamis in the Indus Canyon, NW Indian Ocean, Using Statistical Emulation

The Indus Canyon in the northwestern Indian Ocean has been reported to be the site of numerous submarine mass failures in the past. This study is the first to investigate potential tsunami hazards associated with such mass failures in this region. We employed statistical emulation, i.e. surrogate modelling, to efficiently quantify uncertainties associated with slump-generated tsunamis at the slopes of the canyon. We simulated 60 slump scenarios with thickness of 100–300 m, width of 6–10.5 km, travel distances of 500–2000 m and submergence depth of 250–450 m. These scenarios were then used to train the emulator and predict 500,000 trial scenarios in order to study probabilistically the tsunami hazard over the near field. Due to narrow–deep canyon walls and the shallow continental shelf in the adjacent regions (<100 m water depth), the tsunami propagation has a unique pattern as an ellipse stretched in the NE–SW direction. The results show that the most likely tsunami amplitudes and velocities are approximately 0.2–1.0 m and 2.5–13 m/s, respectively, which can potentially impact vessels and maritime facilities. We demonstrate that the emulator-based approach is an important tool for probabilistic hazard analysis since it can generate thousands of tsunami scenarios in few seconds, compared to days of computations on High Performance Computing facilities for a single run of the dispersive tsunami solver that we use here.

Effect of kinematic fault rupture process on tsunami propagation

The scope of this study is to investigate the effect of the kinematic rupture process on tsunami propagation and corresponding tsunami hazards in coastal regions. It is significant for the tsunageneric earthquakes of long fault length and subsequent long duration of the fault rupture in the strike direction. Most previous studies on the tsunami hazard assessments of the Manila Trench did not consider the effect of the rupture process of huge plates. The movements of the seabed near the earthquake source are calculated by Okada model. The free surface elevation triggered by the seafloor motion is modeled by the nonlinear shallow water equations. The 2004 Indian Ocean tsunami and the 2011 Japan Tohoku tsunami are used to validate the numerical model by comparing with measurement data. The numerical experiments of the tsunami propagation for the cases of different source rupture velocities in uniform depth and continental shelf are carried out to understand the mechanism of the changes of the tsunami arrival time and the tsunami amplitude due to the kinematic rupture process. Stimulated by the long duration of plate motion of 2004 Indian Ocean tsunami, we propose several typical patterns of the rupture process of the long fault of the Manila Trench and analyze quantitatively on the role of the uncertain rupture process of tectonics source in tsunami propagation in the South China Sea. Our results have highlighted that the slow rupture velocity will remarkable affect the tsunami arrival time and maximum amplitude in the South China Sea, comparing to the instantaneous rupture. It is suggested that the rupture process is essential for assessments of the tsunami hazards generated by submarine mass failure with extreme long earthquake rupture source.

Analysis of generation and arrival time of landslide tsunami to Palu City due to the 2018 Sulawesi earthquake

Tsunami waves severely damaged the densely populated coast of Palu City immediately after the 2018 Mw 7.5 Sulawesi earthquake. Among the several tsunami waves that arrived to the city, the two initial waveforms were most likely generated by a landslide at the south-western shore of Palu Bay, about 5 km away from one of the city’s shopping malls. The authors accurately identified the arrival time and direction of the waves by comparing multiple videos taken by a pilot from the cockpit of a plane and local people who witnessed waves approaching the coast. Although the authors’ bathymetric survey only covered a limited area of 0.78 km2, it was found that about 3.2 million m3 of mass disappeared from it, causing a maximum decrease in the seabed elevation of 40 m. A landslide scarp up to 5 m height was also investigated in the southwestern shore of the bay, which seems to be relatively minor compared to the submarine mass failure. Visible clue for liquefaction was not observed at this particular site. A simplified numerical model suggests that the landslide tsunami propagated as an edge wave and split into two separate waves due to the presence of an underwater shallow area just north of Palu City. Both waves arrived to the coast of this city within several minutes: one from North-West and the other from the North. Three major waves were witnessed by residents, who felt horizontal and vertical ground movements and heard the sound of an explosion just after the earthquake. Wave splash exceeded the height of trees on the beach. Given the results, the authors conclude that any modern early warning system is unlikely to work well against such short-warning time tsunamis, and thus, it is necessary for disaster risk managers to consider a way to help people quickly become aware of the potential disaster and evacuate.

SUBMARINE MASS FAILURE: WAVE GENERATION BY GRANULAR SLIDES

Submarine mass failures (SMF) are a potential source of hazardous tsunamis. While the link between seismic events and the magnitude of tsunami waves has been extensively studied and corresponding approaches are included in numerical tsunami warning models, the basic implementation of SMF generated waves is subject to ongoing research. In this context, laboratory experiments are essential for the validation of numerical schemes. Most experimental studies apply rigid slide models whereas only few include granular slides (e.g. Watts 1997, Ataie-Ashtiani &amp; Najafi-Jilani 2008, Grilli et al. 2017). The objective of this study is to gain a better insight into the hydraulic processes related to wave generation by submarine granular slides based on experiments as well as establishing a comprehensive data set for the validation of numerical models.

Landslide Tsunami Hazard Along the Upper US East Coast: Effects of Slide Deformation, Bottom Friction, and Frequency Dispersion

Numerical simulations of Submarine Mass Failures (SMFs) are performed along the upper US East Coast to assess the effect of slide deformation on predicted tsunami hazard. Tsunami generation is simulated using the three-dimensional non-hydrostatic model NHWAVE. For rigid slumps, the geometry and law of motion are specified as bottom boundary conditions. Deforming slide motion is modeled using a depth-integrated bottom layer of dense Newtonian fluid, fully coupled to the overlying fluid motion. Once the SMFs are no-longer tsunamigenic, tsunami propagation simulations are performed using the Boussinesq wave model FUNWAVE-TVD, using nested grids of increasingly fine resolution towards shore and employing a one-way coupling methodology. Probable maximum tsunamis are simulated for Currituck SMF proxies sited in four areas of the shelf break slope that have enough sediment accumulation to cause large failures. Deforming slides have a slightly larger initial acceleration, but still generate a smaller tsunami than rigid slumps due to their spreading and thinning out during motion, which gradually makes them less tsunamigenic. Comparing the maximum envelope of surface elevations along a 5 m isobath, consistent with earlier work, the bathymetry of the wide shelf is found to strongly control the spatial distribution of tsunami inundation. Overall, tsunamis caused by rigid slumps are worst case scenarios, providing up to 50% more inundation than for deforming slides having a moderate level of viscosity set in the upper range of debris flows. Tsunamis from both types of SMFs are able to cause water withdrawal to the 5 m isobath or deeper. Bottom friction effects are assessed by performing some of the simulations using two different Manning coefficients, one 50% larger than the other. With increased bottom friction, the largest tsunami inundations at the coast are reduced by up to 15%. Selected simulations are rerun by turning off dispersion in the model, which leads to moderate changes in maximum surface elevations nearshore (− 10 to + 5% changes), but to more significant effects in the far field (− 40 to 80% changes). Onshore, dispersion causes the appearance of short period undular bores that eventually break nearshore without significantly affecting inundation at the coast. However, these bores increase wave-induced maximum flow velocity and impulse forces, the latter by up to 40%, which may affect the design of coastal structures.

Comparing methods for computation of run-up heights of landslide-generated tsunami in the Northern Sicily continental margin

The North Sicily continental margin is a very active region located in the Central Mediterranean. Strong seismicity, active tectonics and volcanism, fluid escape, high sediment supply, and widespread mass movements historically have exposed this region to marine geohazards, with a potential for tsunami generation. Morpho-bathymetric analysis revealed that one of the most common mechanisms associated with marine geohazards is due to submarine mass failure processes, genetically linked to the other processes active in this margin. With the aim to assess the risks associated with landslide-generated anomalous waves, we selected two sectors of this margin, Gulf of Palermo to the west and Patti offshore to the east. The workflow included analysis of the morpho-bathymetric data, morphometric characterization, calculation of parameters of landslide-generated waves, and computation of run-ups by using different algorithms. Assuming that each of the identified landslides could be a potential tsunamigenic source, we calculated the associated theoretical run-ups, referring to the main computation methodologies proposed in the scientific literature. In order to identify the methodology that better suits run-up values for landslide-generated tsunami, we compared the known run-up values of actual, historical cases with those calculated through the different methodologies. The values obtained with the most suitable equation, both for theoretical and historical events, fit a curve that we used to formulate an empirical law describing the relationships between amplitude and depth, at the source point, and relative run-up. It can be used to calculate easily and promptly the run-up associated with a generic landslide-generated tsunami.

Postrift deltaic sedimentation in western Kachchh Basin: Insights from ichnology and sedimentology

The postrift stage in the pericratonic Kachchh Rift Basin of western India is represented by a thick sequence of a diachronous megadelta system. The deposition of this deltaic sequence was initiated during the mid-Kimmeridgian and ended in the Albian. The sedimentation was interrupted by two transgressive events demarcating three subcycles within the megadelta system. The present study addresses the older mid-Kimmeridgian to Tithonian “Jhuran Delta”. An attempt is made here to delineate the nature of the Jhuran Delta using the ichnological and sedimentological parameters. The Jhuran Delta, which consists of 14 lithofacies, is grouped into seven lithofacies associations corresponding to the prodelta, subaqueous gravity flow, delta front, distributary channel, distributary mouth bar, and shoreface depositional environments along with a transgressive unit overlapping the lower delta of the megadelta system. Three distinct stages of deltaic evolution are delineated along with the fourth stage of transgression and delta destruction. The prodelta environment of Stage I is characterized by moderate ichnodiversity represented by nine recurring ichnotaxa, suggesting alternating brackish and fully saline water conditions, which indicate river-dominated deltaic sedimentation. Stage II shows a marked increase in the influence of river (fresh water) water, as indicated by a submarine mass failure that includes debris flow, chaotic and contorted structures, sediment gravity-failure and water-escape structures and suggesting a higher rate of sedimentation. Ichnologically, this phase indicates low ichnodiversity with sporadic occurrences of Ophiomorpha and Palaeophycus. Stage III indicates the mixed dominance of river and wave processes. Sediments deposited in the delta front environment show moderate ichnodiversity with nine ichnotaxa. The distributary mouth bar environment comprises 6 recurring ichnotaxa including the ichnoassemblages of both river and marine wave environments. Integrated ichnological data suggest deposition in a mixed environment. The Jhuran Delta stage ended with a marine transgressive event and reworking of the deltaic sands, which were overlain by a thick shoreface deposit. Thus, the Upper Jurassic Jhuran Delta represents a river-dominated, wave-influenced delta.