Tsunamigenic Potential Research Articles

Fast and full characterization of large earthquakes from prompt elastogravity signals

Prompt ElastoGravity Signals are light-speed gravity-induced signals recorded before the arrival of seismic waves. They have raised interest for early warning applications but their weak amplitudes close to the background seismic noise have questioned their actual potential for operational use. A deep-learning model has recently demonstrated its ability to mitigate this noise limitation and to provide in near real-time the earthquake magnitude (Mw). However, this approach was efficient only for large earthquakes (Mw ≥ 8.3) of known focal mechanism. Here we show unprecedented performance in full earthquake characterization using the dense broadband seismic network deployed in Alaska and Western Canada. Our deep-learning model provides accurate magnitude and focal mechanism estimates of Mw ≥ 7.8 earthquakes, 2 minutes after origin time (hence the tsunamigenic potential). Our results represent a major step towards the routine use of prompt elastogravity signals in operational warning systems, and demonstrate its potential for tsunami warning in densely-instrumented areas.

Strong earthquakes and tsunami potential in the Hellenic Subduction Zone

The tsunamigenic potential of an earthquake depends on its size, source depth and focal mechanism. The Hellenic Subduction Zone (HSZ) has been selected in the paper to study this important issue. The HSZ was ruptured by 11 strong (Mw6.0) earthquakes in the time period 2009–2023. One earthquake ruptured onshore but only three out of ten offshore earthquakes produced tsunamis: 1 July 2009 (Mw6.4), 25 October 2018 (Mw6.8), 5 May 2020 (Mw6.6). For each one of the two more recent earthquakes of 5 May 2020 (tsunamigenic, thrust faulting) and 12 October 2021 (non-tsunamigenic, strike-slip faulting) we developed heterogeneous fault models from the inversion of teleseismic P-waveforms, and homogeneous fault models from published moment-tensor solutions. For each fault model tsunami generation and propagation was numerically simulated based on an advanced phase-resolving wave model with the use of higher-order Boussinesq-type equations. The modelled tsunami mareograms are consistent with tide records of the small tsunami (height ∼30 cm) produced by the 2020 earthquake. For the 2021 earthquake the modelled mareograms showed tsunami-like disturbance with amplitude not exceeding the noise level. The tsunamigenic earthquakes of 2009, 2018 and 2020 shared magnitude Mw≥ 6.4, shallow depth (h<20 km), moderate-to-high dip-angle and thrust faulting or oblique slip with significant thrust component. In the remaining seven non-tsunamigenic earthquakes, including the 2021 one, at least one of these features is missing. The results obtained help to better understand the seismic mechanisms of tsunami generation in the HSZ. Further investigation is needed for the central HSZ segment to the south of Crete Island, which historically has not been ruptured by large (Mw>7.0) tsunamigenic earthquakes. In contrast, the western and eastern HSZ segments ruptured by the large 365 AD and 1303 AD tsunamigenic earthquakes.

Linked and fully coupled 3D earthquake dynamic rupture and tsunami modeling for the Húsavík–Flatey Fault Zone in North Iceland

Abstract. Tsunamigenic earthquakes pose considerable risks, both economically and socially, yet earthquake and tsunami hazard assessments are typically conducted separately. Earthquakes associated with unexpected tsunamis, such as the 2018 Mw 7.5 strike-slip Sulawesi earthquake, emphasize the need to study the tsunami potential of active submarine faults in different tectonic settings. Here, we investigate physics-based scenarios combining simulations of 3D earthquake dynamic rupture and seismic wave propagation with tsunami generation and propagation. We present time-dependent modeling of one-way linked and 3D fully coupled earthquakes and tsunamis for the ∼ 100 km long Húsavík–Flatey Fault Zone (HFFZ) in North Iceland. Our analysis shows that the HFFZ has the potential to generate sizable tsunamis. The six dynamic rupture models sourcing our tsunami scenarios vary regarding hypocenter location, spatiotemporal evolution, fault slip, and fault structure complexity but coincide with historical earthquake magnitudes. Earthquake dynamic rupture scenarios on a less segmented fault system, particularly with a hypocenter location in the eastern part of the fault system, have a larger potential for local tsunami generation. Here, dynamically evolving large shallow fault slip (∼ 8 m), near-surface rake rotation (± 20∘), and significant coseismic vertical displacements of the local bathymetry (± 1 m) facilitate strike-slip faulting tsunami generation. We model tsunami crest to trough differences (total wave heights) of up to ∼ 0.9 m near the town Ólafsfjörður. In contrast, none of our scenarios endanger the town of Akureyri, which is shielded by multiple reflections within the narrow Eyjafjörður bay and by Hrísey island. We compare the modeled one-way linked tsunami waveforms with simulation results using a 3D fully coupled approach. We find good agreement in the tsunami arrival times and location of maximum tsunami heights. While seismic waves result in transient motions of the sea surface and affect the ocean response, they do not appear to contribute to tsunami generation. However, complex source effects arise in the fully coupled simulations, such as tsunami dispersion effects and the complex superposition of seismic and acoustic waves within the shallow continental shelf of North Iceland. We find that the vertical velocity amplitudes of near-source acoustic waves are unexpectedly high – larger than those corresponding to the actual tsunami – which may serve as a rapid indicator of surface dynamic rupture. Our results have important implications for understanding the tsunamigenic potential of strike-slip fault systems worldwide and the coseismic acoustic wave excitation during tsunami generation and may help to inform future tsunami early warning systems.

Toward the Rapid Seismic Assessment of Landslides in Coastal Alaska

Abstract As glaciers retreat, landslide-driven tsunamis pose mounting threats across the high latitudes. The recent landslide tsunamis in Alaska and Greenland have spurred efforts to forecast and monitor these events. We use nine large landslides spanning southern Alaska to test an approach for rapid detection and characterization. We use long-period seismograms recorded within three minutes of the start of a landslide to estimate the location and approximate volume. In the presence of good seismic network coverage, location errors are no more than a few kilometers, and detection limits are well below 1 Mm3. The combination of detection time, location, and size provides the ability to rapidly determine whether a landslide occurred close to open water and, if so, its tsunamigenic potential. Our approach is rapid enough to support National Oceanic and Atmospheric Administration (NOAA)’s five-minute tsunami warning goal. The historical analysis we present provides the foundation and parameter tuning for a prototype system that is now providing real-time detections.

Compilation of Regional Homogeneous Seismic Catalog for Identification of Tsunamigenic Zones in the Black Sea Region

Although tsunamis in the Black Sea are rare and less destructive, recently, their study has been the subject of interest due to the increasing concentration of population and infrastructure in low-lying coastal areas. This study aims to elucidate the spatial–temporal characteristics of earthquakes in the Black Sea region (27° E–42° E and 40° N–47° N) over a century to clarify the seismicity pattern further to be used for probabilistic seismic and tsunami hazard analysis. Significant volumes of seismic data from international and national databases were analyzed, and the results obtained from previous research were supplemented and expanded. Earthquakes over the period 1905–2022 from eight up-to-date seismic catalogs were used to compile a unified catalog after conversion to the moment magnitude scale Mw. The best-fit linear relationship between several magnitude scales and Mw was determined using the general orthogonal regression (GOR) and the least squares method (LSM). After the declustering procedure, the compiled catalog consists of 18,528 unique events. To assess the catalog data quality, the magnitude of completeness Mc was estimated for the entire catalog (1905–2022) and the so-called instrumental catalog (1977–2022). In addition, the spatial distribution of the completeness magnitude Mc and the recurrence b-plot slope in the Gutenberg–Richter distribution law were assessed using the goodness-of-fit and maximum likelihood methods from the instrumental catalog data. Finally, the most significant earthquakes within the Black Sea boundaries were estimated with their parameters and focal mechanisms. A possibility of the realization of strong quakes in the near future with tsunamigenic potential in the Black Sea region was concluded.

Seismic source identification of the 9 November 2022 Mw 5.5 offshore Adriatic sea (Italy) earthquake from GNSS data and aftershock relocation

The fast individuation and modeling of faults responsible for large earthquakes are fundamental for understanding the evolution of potentially destructive seismic sequences. This is even more challenging in case of buried thrusts located in offshore areas, like those hosting the 9 November 2022 Ml 5.7 (Mw 5.5) and ML 5.2 earthquakes that nucleated along the Apennines compressional front, offshore the northern Adriatic Sea. Available on- and offshore (from hydrocarbon platforms) geodetic observations and seismological data provide robust constraints on the rupture of a 15 km long, ca. 24° SSW-dipping fault patch, consistent with seismic reflection data. Stress increase along unruptured portion of the activated thrust front suggests the potential activation of longer portions of the thrust with higher magnitude earthquake and larger surface faulting. This unpleasant scenario needs to be further investigated, also considering their tsunamigenic potential and possible impact on onshore and offshore human communities and infrastructures.

Cohesion, permeability, and slope failure dynamics: Implications for failure morphology and tsunamigenesis from benchtop flume experiments

Submarine slope failures pose hazards to coastal communities through their ability to damage seafloor infrastructure and generate tsunamis. Submarine slope failures occur along continental margins worldwide, yet our understanding of submarine slope failure evolution and tsunamigenic potential is limited. Overpressure has been a proposed mechanism for initiating and preconditioning for slope failures, but understanding of its role in slope failures is limited. In this study, we investigate overpressure-induced slope failures with different sediment compositions and properties common in the marine environment. Overpressure required for slope failure and failure behavior were investigated in relation to sediment permeability and cohesion. We investigated failures in benchtop flume experiments using mixtures of fine-grained quartz sand and cohesive smectite clay or fine-grained quartz sand and non-cohesive clay-sized quartz. In high-permeability, sand-rich systems (0–5 wt% smectite), overpressure required to induce failure directly related to smectite content (R2 of 0.89). At smectite concentrations of 25 wt% or greater, normalized overpressure (λ*) required to induce slope failure remained constant at λ* = 1.52 ± 0.55. Failure behavior also changed at 25% smectite. In sand-rich systems, a single failure event occurred even with sustained or increased overpressure. With smectite or clay-sized quartz concentrations of 25 wt% or higher, a series of slope failures occurred. Concentrations of smectite ≥25% also produced larger and more brittle failure deformation features (e.g., tension cracks and subsurface fissures). We conclude that lower permeability systems have the potential for larger failures and cohesive sediment mixtures are necessary for producing brittle failure features (e.g., tension cracks, subsurface fissures, rafted blocks, etc.). Experiments using 25, 75, and 90 wt% smectite produced rafted sediment blocks separated from the parent slope. However, experiments did not mobilize any intact blocks downslope even with a relatively steep (19°) slope. Observed experiment failure deformation features (e.g., mud-volcanism, tension cracks, clay-enriched toe deposits, etc.) match observed phenomenon in natural marine environments. From our experiments, we interpret in the presence of low-permeability, high-cohesion sediments, overpressure can produce non-tsunamigenic submarine slope failures and precondition slopes for tsunamigenic failure. Thus, our work demonstrates the importance of sediment properties and composition in relation to the types of failures produced and additionally emphasize the need for multiple factors (e.g., excess head plus seismic shaking) to mobilize large, rafted blocks downslope which has direct impact in improving coastal hazard assessment.

Rapid shallow megathrust afterslip from the 2021 M8.2 Chignik, Alaska earthquake revealed by seafloor geodesy.

The shallower portions of subduction zone megathrust faults host Earth's most hazardous tsunamigenic earthquakes, yet understanding how and when they slip remains elusive because of challenges making seafloor observations. We performed Global Navigation Satellite System Acoustic seafloor geodetic surveys before and ~2.5 months after the 29 July 2021 Mw (moment magnitude) 8.2 Chignik, Alaska, earthquake and determine ~1.4 meters cumulative co- and post-seismic horizontal displacement ~60 kilometers from the megathrust front. Only for the 2011 Mw 9 Tohoku event have closer subduction zone earthquake displacements been observed. We estimate ~2 to 3 meters of megathrust afterslip shallower than 20 kilometers, a portion of the megathrust on which both inter- and co-seismic slip likely had occurred previously. Our analysis demonstrates that by 2.5 months, shallower and deeper moment had effectively equilibrated on the megathrust, suggesting that its tsunamigenic potential remains no more elevated than before the earthquake.

Landslide Induced Tsunami Hazard at Volcanoes: the Case of Santorini

The destructive tsunami on 22 December 2018 due to the flank collapse of the Anak Krakatau volcano was a bitter reminder of large tsunami risks and of the shortcomings of the existing tsunami warning systems for atypical sources (tsunamis generated by non-seismic and complex sources). In the Mediterranean, several tsunamis were generated by landslides associated with volcanic systems in the past.The volcanic unrest experienced in 2011–2012 on the Santorini volcanic island in the Southern Aegean Sea pointed out the need to identify and quantify tsunami hazard and risk due to possible flank instability which may be triggered as a result of volcanic unrest or nearby seismotectonic activities. Inspired from this need, in this study we examined three possible landslide scenarios in Santorini Island with tsunamigenic potential. The results show that the scenarios considered in our study are able to generate significant local tsunamis impacting Santorini and the nearby islands, as well as producing significant impact along the coasts of the Southern Aegean Sea. While maximum tsunami amplitudes/arrival time ranges are 1.2 m/30-90 min for locations in the Greek-Turkish coasts in the far field, they are in the order of ≈60 m/1-2 min for some locations at the Santorini Island. The extreme tsunami amplitudes and short arrival times for locations inside the Santorini Island is a major challenge in terms of tsunami hazard warning and mitigation. As an effort to address this challenge, a discussion on the requirements for local tsunami warning system addressing atypical sources in the context of multi-hazard disaster risk reduction is also provided.

Trench-parallel ridge subduction controls upper-plate structure and shallow megathrust seismogenesis along the Jalisco-Colima margin, Mexico

The parameters allowing for near-trench megathrust ruptures are debated and commonly involve the presence of site-dependent tectonic factors (e.g. rough subducting topography, amount of sediments), implying the need for direct geophysical observations. Here we use seismic imaging techniques to explore the mechanisms triggering shallow ruptures in the Rivera subduction zone, along the non-accretionary Jalisco-Colima continental margin, W Mexico, where three large (Mw~8) tsunamigenic megathrust earthquakes occurred in the last century. The seismic image reveals large interplate topographic variations morphologically alike to incoming trench-parallel ridges seaward of the study area. Ridge subduction only occurs along the southern non-accretionary margin of the Rivera system, where past earthquakes released large near-trench coseismic energy, indicating that subducting ridges enhance interplate coupling. Subducting ridges uplift the margin, causing upper-plate fracturing and low rigidity areas. Such elastic structure quantitatively explains the dynamics of slow and tsunamigenic ruptures in the past. We conclude that ridge subduction beneath the Jalisco-Colima continental margin promotes shallow seismogenesis and explains the large tsunamigenic potential of the area.

Potential tsunami hazard of the southern Vanuatu subduction zone: tectonics, case study of the Matthew Island tsunami of 10 February 2021 and implication in regional hazard assessment

Abstract. The Vanuatu subduction zone (VSZ) is known to be seismically very active, due to the high convergence rate between the Australian and Pacific tectonic plates for the majority of the margin. However, this is not the case on its southernmost part south of latitude 22.5∘ S and east of longitude 170∘ E, which is neither highly tectonically active nor has it produced large tsunamis over the past 150 years. It has also not been widely studied. On the 11 February 2021 (10 February UTC), a magnitude Mw 7.7 earthquake triggered a tsunami warning in New Caledonia and Vanuatu 20 min after midnight (local time). With an epicentre located close to the volcanic islands of Matthew and Hunter, this shallow reverse-faulting rupture (&lt; 30 km depth) was able to deform the seabed and produce a tsunami. This was confirmed 45 min later by the coastal gauges of the Loyalty and the south Vanuatu islands, which recorded the first tsunami waves. Showing a typical recorded amplitude of less than 1 m, with a maximum of ∼ 1.5 m in Lenakel (Tanna, Vanuatu), it was observed on most coastal gauges and DART stations in the south-west Pacific region as far as Tasmania to the south and Tuvalu to the north at distances of ∼ 3000 and ∼ 1800 km from the epicentre. In this study, the tsunamigenic potential of the southernmost part of the VSZ and the implications in terms of regional hazard assessment are discussed through (1) the presentation of the complex tectonic settings of this “transition zone” between the Solomon–Vanuatu and the Tonga–Kermadec trenches, (2) the case study of the 10 February 2021 tsunami at a south-west Pacific regional scale using three different tsunami generation scenarios computed with the COMCOT modelling code on a set of 48 nested bathymetric grids, and (3) the simulation of a plausible Mw 8.2 scenario encompassing the active part of this “transition zone”. The validation of the Mw 7.7 parameters for tsunami modelling provides the means to further assess the hazard from potential tsunamis triggered by higher magnitude earthquakes in this region. Tsunami records highlight that &gt; 28 cm wave amplitudes were recorded at eight different coastal gauges, including one with an amplitude of more than 1 m (Lenakel, Tanna, Vanuatu). The tsunami threat at that location would be large enough to warrant an onshore evacuation. Finally, it helps to highlight the significant role played by the numerous submarine features in the region, the Norfolk Ridge being the most important, which acts like a waveguide from the north to the south.

Earthquake-Induced Tsunamis in Western Greece (Ionian Sea and Western and Southern Peloponnese): Use of Tsunami Quantities, Impact and ITIS-2012 Intensities for Highlighting Susceptible Areas

Taking into account recent studies on the tsunamigenic potential of strike-slip faults, it is concluded that there is a need to reassess their near-source tsunami hazard and risk. One of the areas which needs reassessment is Western Greece, especially the Ionian Islands and the western coastal Peloponnese, where major seismogenic strike-slip structures occur. In this context, an extensive review of the available literature is conducted, including not only earthquake and tsunami catalogues but also tsunamis’ imprints on the stratigraphic record. It is concluded that the Ionian Islands and the western Peloponnese have a rich history of tsunamis since 6000 BC, revealing that they are subjected to high tsunami hazard. In addition to the teletsunami effects of distant earthquakes, there are also local tsunamis with smaller physical quantities and slighter coastal impact that are attributed mainly to local offshore faults and earthquake-triggered landslides. The fact that no destructive local tsunamis have been detected so far does not exclude the possibility of future triggering. In order to identify areas susceptible to future tsunami impact, we extract tsunami quantities and coastal impact data from available sources and we apply the Integrated Tsunami Intensity Scale 2012 (ITIS-2012) for all the events with available and adequate information. The highly susceptible areas comprise straits, funnel-shaped bays and extensive coastal areas exposed to major strike-slip seismogenic sources in the Ionian Sea and the western Hellenic Trench. Based on the aforementioned information, the inclusion of the Ionian Sea in the tsunamigenic zones of Greece is strongly recommended.

The tsunamigenic potential of landslide-generated tsunamis on the Vavilov seamount

The investigation of submarine volcanoes and the tsunamigenic potential of possible movements on their flanks is arduous. In most cases, the lack of specific information about the eruptions' history and their consequences does not allow a comprehensive analysis in terms of hazard. Nevertheless, useful clues on the possible occurrence of mass movements on seamounts can be obtained from a series of research fields. These account for morphological studies, observations of hydrothermal activity, collection of geophysical data (for example, detailed DEM, seismic profiles, magnetic data), etc. In this context, this study presents new bathymetric data of the Vavilov submarine volcano (Tyrrhenian Sea, Italy) and a detailed morphological analysis of the structure. The latter allows the identification of zones potentially prone to mass movements and the development of numerical scenarios to investigate the tsunami potential associated to these movements on the Vavilov flanks. Results prove that the waves generated by the mass displacements in the proposed scenarios (involving sliding volumes between 0.32 km3 and 1.7 km3) reach maximum values in the order of centimetres, not considering dispersive effects. Eventually, a scenario involving the partial collapse of the west flank of the Vavilov Seamount is simulated, although the occurrence of such an event in the past is still debated due to the uncertainties related to the origin and development of the volcano dome. In this scenario, water elevation as high as 10 m are found in large portions of the Tyrrhenian coasts: waves are large enough to emplace sizeable tsunami deposits onshore, that could have been preserved until today in some specific stretches of the coast and could be detected by a finalised geological search. This study belongs to a series of works devoted to the submarine structures of the Tyrrhenian Sea aiming to disclose the tsunamigenic potential of submarine mass movements on their flanks.

Experimental Modeling of Tsunamis Generated by Pyroclastic Density Currents: The Effects of Particle Size Distribution on Wave Generation

AbstractVolcanic tsunamis can expand the radius of hazards posed by a volcano well beyond the reach of the eruption itself; however, their source mechanisms are poorly understood. The tsunamigenic potential of pyroclastic density currents was studied experimentally by releasing a fluidized column of glass beads from a reservoir; the beads then ran down an inclined ramp into a water‐filled flume and generated waves. The effects of the particle size distribution on the generated waves were analyzed by comparing the waves generated by flows comprising different proportions of particles of diameters 63–90 μm and 600–850 μm. The flows comprising higher proportions of large particles travel more slowly down the ramp; however, all the flows impact the water at velocities greater than the shallow water wave speed, , where h is the still‐water depth. The entrance of the fluidized flow into the water generates a solitary‐like leading wave followed by a smaller trough and trailing waves. Upon impact, the flow separates into a part advected with the wave crest and a part which turbulently mixes with water and propagates along the bottom of the flume, forming an underwater gravity current. A higher proportion of large particles makes the flows more porous, allowing the water to penetrate through the flows more easily, slightly decreasing the efficiency of the energy transfer. While this affects the celerity of the waves, the results show that, over the studied range of particle size distributions, all the flows can generate waves of similar amplitudes regardless of the particle size distribution.

Submarine canyons and slides in the central-west Otway Basin: their morphology, genesis, links to groundwater discharge and tsunamigenic potential

The morphology and development of several submarine canyons offshore southeast South Australia and western Victoria are described. The existence of three of those canyons had been foreshadowed in 1963 by N. Boutakoff, who thought them to be linked to ancient courses of the Glenelg River. These canyons occur on the outer continental shelf where their heads are situated in depths shallower than 1000 m. Sinuous channels are visible within two of the canyon heads, indicating that water and sediment may still travel downslope and cause erosion, and thus are geologically recent. Several other canyons are also documented and named. Two canyons are confined to depths below 3000 m; they may be much older and seem not to be linked to ancient river courses. They are also oblique to the upper canyons. The other characteristic feature of the area is the presence of numerous undersea slides. These occur at three specific depths (∼1200, ∼1500 and ∼1800 m) and are coincident with stratigraphic horizons in which continental groundwater flows have been identified in adjacent exploratory oil and gas wells drilled into the continental shelf. Sapping of groundwater may likely have occurred during very wet periods inland. We suggest that these undersea slides could be the first step in the formation of deep-sea canyons that are not necessarily linked to ancient river courses. We also postulate that the ‘sliding’ of large piles of sediment down the continental slope has tsunamigenic potential and may have occurred during significant wet climate on land. KEY POINTS Several deep-sea canyons and numerous submarine slides are documented along the continental shelf offshore the coastline of western Victoria and southeast South Australia in the Otway Basin. Some of these canyons are linked to previous courses of the Glenelg River, which changed over time in response to regional tectonic changes such as faulting and significant upwarping. The orientation of most of these canyons tends to align with ancient terrestrial lineaments that likely extend offshore. Sinuous channels within the upper canyon reaches are clearly visible and not infilled with sediment; they are likely active and linked to ongoing groundwater seepage. It is proposed that the underwater slides are generated by the submarine discharge of continental groundwater on the continental slope, at three specific water depths with discharge associated with particular lithologies. These slides may still be active. Superimposed slides may engender the formation of new canyons. The volume of some of these undersea slides is of tsunamigenic scale.

Evaluating the Tsunamigenic Potential of Buried Versus Trench‐Breaching Megathrust Slip

AbstractSubduction megathrust ruptures that breach the trench, such as in the 2011 M = 9 Tohoku‐oki earthquake, can be very tsunamigenic. However, whether buried ruptures are intrinsically less tsunamigenic has not been fully investigated. Here, we conduct this investigation by studying the mechanics of seafloor deformation and the resultant tsunami runup. With a trench‐breaching rupture, deformation is dominated by the rigid‐body translation of the frontal upper plate, and seafloor uplift is enhanced by the horizontal motion of the sloping seafloor. With a buried rupture, the rigid‐body motion is reduced, but the shortening of the upper plate due to seaward slip termination causes elastic thickening to enhance tsunamigenic seafloor uplift. By combining a finite‐element deformation model and a shallow‐water equation tsunami model, we systematically test various subduction zone geometrical and slip parameters to study the trade‐off between rigid‐body translation and elastic thickening in causing seafloor uplift and tsunami runup. To isolate the effect of slip depth, we compare scenarios with the same peak slip and rupture width. We find that very shallow ruptures, including those breaching the trench, are generally less tsunamigenic than deeper ruptures. Given peak slip, tsunamigenic potential is maximized if the rupture is not too shallow or too deep but is buried to moderate depths. Our model tests using variable hypothetical rupture depths suggest that, with a slip magnitude as large as in the 2011 Tohoku‐oki earthquake, tsunami runups as high as the observed would occur even if the rupture were fully buried.

Submarine Landslides in the West Continental Slope of the South China Sea and Their Tsunamigenic Potential

The 109 meridian fault is located in the west of the South China Sea (SCS) connecting to the offshore Red River Shear Zone. Seismic data from the central Vietnamese shelf indicates that many submarine landslides were developed along the steep continental slope in this offshore region. Here, we analyze the potential for such landslides to trigger damaging tsunamis based on the local geological background and sedimentary environment. We assess their tsunamigenic potential along the coast of Southern Central Vietnam (SCV). We point out that the evolutionary processes of the 109° meridian fault: striking-subsidence of the adjacent basin, combined with the high sediment input from numerous montane rivers of the hinterland generate conditions that likely favor the development of submarine landslides along the well-defined and steep continental slope near SCV. To estimate the impact of tsunami waves on the SCV coastline, we conducted a pilot study using two numerical models: NHWAVE and FUNWAVE-TVD to model 4 representative landslides with volumes ranging between 1.3 and 14 km3 and water depth of 300–1000 m. The submarine landslides were treated as rigid slump and deformable slide corresponding to two different sedimentary environments. Our results show that the tsunami waves generated by rigid slump can reach up to 20 m height in the landslide source area and ∼5 m when arriving at the closest coastline. Tsunami waves could arrive at the central Vietnam coast within 30 min in eight scenarios. Our initial results also suggest that seafloor topography, i.e., waveguide effects of ocean ridges, shelf resonance and the potential bay resonance cause significant variability in potential run-up. We note that ocean ridges located in the deep basin of the SCS focus the tsunami energy propagating towards the northwest coast of Luzon Island, Philippines where tsunami wave heights of ∼2.3 m wave height are modeled. These findings underscore the importance of tsunami hazard assessments that account for both earthquake generated and earthquake triggered tsunamis. Our work also highlights a continued need to examine tsunami sources in the region as mitigation and preparedness for the socio-economically important and heavily populated coastlines of the SCS is reliant on a detailed understanding of the hazard.

A first appraisal of the seismogenic and tsunamigenic potential of the largest fault systems in the westernmost Mediterranean

The westernmost Mediterranean hosts part of the plate boundary between the European and African tectonic plates. Based on the scattered instrumental seismicity, this boundary has been traditionally interpreted as a wide zone of diffuse deformation. However, recent seismic images and seafloor mapping studies support that most of the plate convergence may be accommodated in a few tectonic structures, rather than in a broad region. Historical earthquakes with magnitudes Mw > 6 and historical tsunamis support that the low-to-moderate instrumental seismicity might also have led to underestimation of the seismogenic and tsunamigenic potential of the area. We evaluate the largest active faults of the westernmost Mediterranean: the reverse Alboran Ridge, and the strike-slip Carboneras, Yusuf and Al-Idrissi fault systems. For the first time, we use a dense grid of modern seismic data to characterize the entire dimensions of the main fault systems, accurately describe the geometry of these structures and estimate their seismic source parameters. Tsunami scenarios have been tested based on 3D-surfaces and seismic source parameters, using both uniform and heterogeneous slip distributions. The comparison of our results with previous studies, based on limited information on the fault geometry and kinematics, indicates that accurate fault geometries and heterogeneous slip distributions are needed to properly assess the seismic and tsunamigenic potential in this area. Based on fault scaling relations, the four fault systems have a large seismogenic potential, being able to generate earthquakes with Mw > 7. The reverse Alboran Ridge Fault System has the largest tsunamigenic potential, being able to generate a tsunami wave amplitude greater than 3 m in front of the coasts of Southern Spain and Northern Africa.

Tsunamigenic Potential of an Incipient Submarine Landslide in the Tiran Straits

AbstractThe Red Sea is a maritime rift. Tsunamigenic submarine landslides are common in these deep, steep‐sided, and seismically active basins. Because the rift is narrow, tsunami formed on one margin dissipate little before impacting the opposite side. Red Sea slope failures are therefore especially hazardous. We examine the tsunamigenic potential of an incipient landslide in the Tiran Straits that started, but then stopped after a short distance. Radiometric and biotic analyses fix the age of this landslide to within the last 500 years. Tsunami modeling of the incipient slide predicts ∼10 m wave heights on the Egyptian coastline. Of present concern is that the slope will eventually slide to completion with even more hazardous results. Tsunami simulated for this future event are twice as large as that generated by the incipient slide, so the threat posed by a future slide is consequential. Sharm El Sheikh, an Egyptian resort town now lies in its path, as does “The Line,” a vast Saudi infrastructure project. This study warns of credible tsunami risk in the rapidly urbanizing Tiran Straits.

The Sensitivity of Tsunami Impact to Earthquake Source Parameters and Manning Friction in High-Resolution Inundation Simulations

In seismically active regions with variable dominant focal mechanisms, there is considerable tsunami inundation height uncertainty. Basic earthquake source parameters such as dip, strike, and rake affect significantly the tsunamigenic potential and the tsunami directivity. Tsunami inundation is also sensitive to other properties such as bottom friction. Despite their importance, sensitivity to these basic parameters is surprisingly sparsely studied in literature. We perform suites of systematic parameter searches to investigate the sensitivity of inundation at the towns of Catania and Siracusa on Sicily to changes both in the earthquake source parameters and the Manning friction. The inundation is modelled using the Tsunami-HySEA shallow water code on a system of nested topo-bathymetric grids with a finest spatial resolution of 10 m. This GPU-based model, with significant HPC resources, allows us to perform large numbers of high-resolution tsunami simulations. We analyze the variability of different hydrodynamic parameters due to large earthquakes with uniform slip at different locations, focal depth, and different source parameters. We consider sources both near the coastline, in which significant near-shore co-seismic deformation occurs, and offshore, where near-shore co-seismic deformation is negligible. For distant offshore earthquake sources, we see systematic and intuitive changes in the inundation with changes in strike, dip, rake, and depth. For near-shore sources, the dependency is far more complicated and co-determined by both the source mechanisms and the coastal morphology. The sensitivity studies provide directions on how to resolve the source discretization to optimize the number of sources in Probabilistic Tsunami Hazard Analysis, and they demonstrate a need for a far finer discretization of local sources than for more distant sources. For a small number of earthquake sources, we study systematically the inundation as a function of the Manning coefficient. The sensitivity of the inundation to this parameter varies greatly for different earthquake sources and topo-bathymetry at the coastline of interest. The friction greatly affects the velocities and momentum flux and to a lesser but still significant extent the inundation distance from the coastline. An understanding of all these dependencies is needed to better quantify the hazard when source complexity increases.