Tsunami Propagation Research Articles

Development of a Numerical Model Considering Active Tsunami Generation

Seabed deformation due to the fault failure have both a spatial variation and temporal history. When the faulting process initiates at a certain point beneath seabed, the failure spreads out to neighboring points, resulting in temporal changes of deformation. In particular, such a process induces tsunami waves from the vertical motion of seabed. The uprising speed of seabed affects the formation of initial surface profile, eventually altering the arrival time and runup of tsunamis at the coast. In this work, we developed a numerical model that can simulate the generation and propagation of tsunami waves by considering the horizontal and vertical changes of seabed in an active and dynamic manner. For the verification of the model, it was applied to the 2011 Tohoku-oki earthquake in Japan and the results confirmed that the accuracy was improved compared to the existing passive and static model.

Tsunami generation potential of a strike-slip fault tip in the westernmost Mediterranean

Tsunamis are triggered by sudden seafloor displacements, and usually originate from seismic activity at faults. Nevertheless, strike-slip faults are usually disregarded as major triggers, as they are thought to be capable of generating only moderate seafloor deformation; accordingly, the tsunamigenic potential of the vertical throw at the tips of strike-slip faults is not thought to be significant. We found the active dextral NW–SE Averroes Fault in the central Alboran Sea (westernmost Mediterranean) has a historical vertical throw of up to 5.4 m at its northwestern tip corresponding to an earthquake of Mw 7.0. We modelled the tsunamigenic potential of this seafloor deformation by Tsunami-HySEA software using the Coulomb 3.3 code. Waves propagating on two main branches reach highly populated sectors of the Iberian coast with maximum arrival heights of 6 m within 21 and 35 min, which is too quick for current early-warning systems to operate successfully. These findings suggest that the tsunamigenic potential of strike-slip faults is more important than previously thought, and should be taken into account for the re-evaluation of tsunami early-warning systems.

Landslide-tsunamis along the flanks of Mount Epomeo, Ischia: propagation patterns and coastal hazard for the Campania Coasts, Italy

Abstract Ischia Island has been repeatedly affected by mass collapses, which are mainly caused by the steepness of the main peak (Mt Epomeo) and by phenomena related to its volcanic activity. The most relevant cases of mass failure studied in the literature and postulated to be tsunamigenic cover a wide spectrum of sizes, from sector collapse to small-volume mass transports. Tsunamis generated by landslides in Ischia may affect the coast of the Campania mainland, including the Gulf of Naples. The focus of this work is an evaluation of the pattern of the maximum tsunami energy. To this purpose, we perform a series of numerical simulations by moving the same landslide source in different hypothetical positions around the island. The landslide dynamics are computed through the code UBO-BLOCK, and the tsunami propagation by employing the code UBO-TSUFD, both developed in-house. The final goal is to characterize the coastal areas of the Campania mainland most exposed to tsunami attack from Ischia sources. It is found that the position of the landslide deeply influences the distribution of the tsunami elevation in the coastal stretch north of the Procida Mt, while, remarkably, it is irrelevant inside the Gulf of Naples where the bathymetric effect prevails.

Impulsive Tsunami and Large Runup Along the Sanriku Coast of Japan Produced by an Inelastic Wedge Deformation Model

AbstractDynamic wedge failure produces short‐wavelength seafloor uplift efficiently with diminishing shallow slip on the plate interface, generating impulsive tsunami. For ria coasts with prevalent small‐wavelength bathymetric and geomorphologic features, such as the Sanriku coast of Japan, impulsive tsunami can be amplified to produce large runup. We model tsunami propagation and runup of the 1896 Sanriku tsunami by using the seafloor deformation from dynamic rupture models of Ma and Nie (2019) for a MW 8 earthquake with inelastic wedge deformation. The nonlinear Boussinesq equation is solved by a nested‐grid finite‐difference method with high‐resolution bathymetry data. We show that an inelastic deformation model with extensive wedge failure produces impulsive tsunami similar to those observed offshore the Sanriku coast in the 2011 Tohoku earthquake and generates large runup remarkably consistent with the 1896 Sanriku tsunami. As an alternative to previous models based solely on fault slip, we suggest that the impulsive tsunami and large runup along the Sanriku coast observed in the 2011 Tohoku earthquake can be explained by inelastic wedge deformation north of 38.5°N.

Modeling of the Dec. 22nd 2018 Anak Krakatau volcano lateral collapse and tsunami based on recent field surveys: Comparison with observed tsunami impact

The Dec. 22, 2018 lateral collapse of the Anak Krakatau (AK) volcano in the Sunda Straits of Indonesia discharged volcaniclastic material into the 250 m deep caldera southwest of the volcano and generated a large tsunami, causing runups of up to 85 m in the near-field, and 13.5 m in the far-field, on the nearby coasts of Sumatra and Java. The tsunami caused 437 fatalities, the greatest number from a volcanically-induced tsunami since the catastrophic explosive caldera-forming eruption of Krakatau in 1883 and the sector collapse of Ritter Island in 1888. For the first time in over 100 years, the 2018 AK event provides an opportunity to study a major volcanically-generated tsunami that caused widespread loss of life and significant damage. Here, we present numerical simulations of the collapse and tsunami generation, propagation, and coastal impact, with state-of the-art numerical models, using both a new parametrization of the collapse and a near-field bathymetric dataset based on our 2019 field surveys and satellite images. These subaerial and submarine data sets are used to constrain the geometry and magnitude of the landslide mechanism, which show that the primary landslide scar bisected the AK edifice, cutting behind the central vent and removing 50% of its subaerial volume. The primary landslide volume is estimated to range from 0.175–0.313 km3, based on uncertainties in the shape of the submerged part of the failure plane. This is supported by an independent estimate of the primary landslide deposit volume of 0.214 ± 0.036 km3. Given uncertainties in the failure volume, we define a range of potential failure surfaces that span these values in 4 collapse scenarios of volume ranging from 0.175 to 0.313 km3. These AK collapses are modeled, assuming either a granular or viscous fluid rheology, together with their corresponding tsunami generation and propagation. Observations of a single tsunami, with no subsequent waves, are consistent with our interpretation of landslide failure in a rapid, single phase of movement rather than a more piecemeal process, generating a tsunami which reached nearby coastlines within ~30 min. For both modeled rheologies, the 0.224 km3 collapse (second and preferred scenario) most successfully reproduces the near- and far-field tsunami flow depth and runup observed in all post-event field survey results, tide gauge records, and eyewitness reports to date, suggesting our estimated landslide volume range is appropriate. This event highlights the significant hazard posed by relatively small-scale lateral volcanic collapses, which can occur en-masse, without any precursory signals, and are an efficient and unpredictable tsunami source. Our successful simulations demonstrate that current numerical models can accurately forecast tsunami hazards from these events. In cases such as Anak Krakatau's, the absence of precursory warning signals, together with the short travel time following tsunami initiation present a major challenge for mitigating tsunami coastal impact, stressing the need to develop and install early warning systems for such events.

Tsunami propagation kernel and its applications

Abstract. Tsunamis rarely occur in a specific area, and their occurrence is highly uncertain. Suddenly generated from their sources in deep water, they occasionally undergo tremendous amplification in shallow water to devastate low-lying coastal areas. Despite the advancement of computational power and simulation algorithms, there is a need for novel and rigorous approaches to efficiently predict coastal amplification of tsunamis during different disaster management phases, such as tsunami risk assessment and real-time forecast. This study presents convolution kernels that can instantly predict onshore waveforms of water surface elevation and flow velocity from observed/simulated wave data away from the shore. Kernel convolution involves isolating an incident-wave component from the offshore wave data and transforming it into the onshore waveform. Moreover, unlike previously derived ones, the present kernels are based on shallow-water equations with a damping term and can account for tsunami attenuation on its path to the shore with a damping parameter. Kernel convolution can be implemented at a low computational cost compared to conventional numerical models that discretise the spatial domain. The prediction capability of the kernel method was demonstrated through application to real-world tsunami cases.

Seismic reconstruction of seafloor sediment deformation during volcanic debris avalanche emplacement offshore Sakar, Papua New Guinea

Volcanic island sector collapses have produced some of the most voluminous mass movements on Earth and have the potential to trigger devastating tsunamis. In the marine environment, landslide deposits offshore the flanks of volcanic islands often consist of a mixture of volcanic material and incorporated seafloor sediments. The interaction of the initial volcanic failure and the substrate can be highly complex and have an impact on both the total landslide deposit volume and its emplacement velocity, which are important parameters during tsunami generation and need to be correctly assessed in numerical landslide-tsunami simulations. Here, we present a 2D seismic analysis of two previously unknown, overlapping volcanic landslide deposits north-west of the island of Sakar (Papua New Guinea) in the Bismarck Sea. The deposits are separated by a package of well-stratified sediment. Despite both originating from the same source, with the same broad movement direction, and having similar deposit volumes (~15.5–26 km3), the interaction of these landslides with the seafloor is markedly different. High-resolution seismic reflection data show that the lower, older deposit comprises a proximal, chaotic, volcanic debris avalanche component and a distal, frontally confined component of deformed pre-existing well-bedded seafloor sediment. We infer that deformation of the seafloor sediment unit was caused by interaction of the initial volcanic debris avalanche with the substrate. The deformed sediment unit shows various compressional structures, including thrusting and folding, over a downslope distance of more than 20 km, generating >27% of shortening over a 5 km distance at the deposit's toe. The volume of the deformed sediments is almost the same as the driving debris avalanche deposit. In contrast, the upper, younger landslide deposit does not show evidence for substrate incorporation or deformation. Instead, the landslide is a structurally simpler deposit, formed by a debris avalanche that spread freely along the contemporaneous seafloor (i.e., the top boundary of the intervening sediment unit that now separates this younger landslide from the older deposit). Our observations show that the physical characteristics of the substrate on which a landslide is emplaced control the amount of seafloor incorporation, the potential for secondary seafloor failure, and the total landslide runout far more than the nature of the original slide material or other characteristics of the source region. Our results indicate the importance of accounting for substrate interaction when evaluating submarine landslide deposits, which is often only evident from internal imaging rather than surface morphological features. If substrate incorporation or deformation is extensive, then treating landslide deposits as a single entity substantially overestimates the volume of the initial failure, which is much more important for tsunami generation than secondary sediment failure.

Wedge Plasticity and Fully Coupled Simulations of Dynamic Rupture and Tsunami in the Cascadia Subduction Zone

AbstractInelastic wedge deformation likely plays an important role in the generation of tsunami and ocean acoustic waves in accretionary subduction margins. In an elastic dislocation model, whether or not the fault breaks the trench has a significant effect on seafloor deformation and resulting tsunami. However, this boundary condition is less important when significant inelastic deformation in the overriding wedge occurs, because large seafloor uplift can occur with little or no slip at the trench. Here we incorporate wedge plasticity in fully coupled dynamic rupture and tsunami simulations for a buried fault in the Cascadia subduction zone with realistic fault geometry, bathymetry, and velocity structure. A linearized Eulerian approach is verified and used to simulate gravity waves in the ocean. Our coupled models show that the inelastic deformation of wedge sediments can significantly contribute to seafloor uplift, producing tsunami heights at least twice as large as in purely elastic simulations, whilst generating weaker ocean acoustic and seismic waves. Inelastic wedge deformation is therefore an important mechanism to consider in tsunami hazard assessment in the Cascadia subduction zone. These results have important implications for tsunami generation and early warning in accretionary and other sediment‐filled margins worldwide.

Time‐Dependent Probabilistic Tsunami Inundation Assessment Using Mode Decomposition to Assess Uncertainty for an Earthquake Scenario

AbstractThis study presents an innovative probabilistic tsunami inundation assessment for an earthquake scenario to randomly generate tsunami inundation depth distributions by quantitatively evaluating the spatial correlation of tsunami inundation depths using singular value decomposition (SVD) derived from proper orthogonal decomposition and to evaluate the tsunami inundation depths considering the imminent occurrence of an earthquake. We found a good agreement between the evaluation results of the proposed surrogate model and the numerical results of the nonlinear long wave equations for the tsunami inundation depth distribution in Kamakura city, Japan, due to the Sagami Trough megathrust earthquake. Evaluating the spatial correlation using SVD has the advantage that the covariance matrix does not need to be defined in advance but can be defined from the data itself. We also achieved a significant reduction in the number of required tsunami propagation simulations for the probabilistic assessment and attained higher computational efficiency by extracting spatial correlations with SVD. Furthermore, we conducted a probabilistic tsunami inundation assessment focusing on a relatively short period (i.e., 50 years) considering the time‐dependent occurrence probability of the target earthquake. The proposed probabilistic assessment method with mode decomposition is applicable to the general probabilistic tsunami hazard assessment by integrating it with physical stochastic slip models.

3D Linked Subduction, Dynamic Rupture, Tsunami, and Inundation Modeling: Dynamic Effects of Supershear and Tsunami Earthquakes, Hypocenter Location, and Shallow Fault Slip

Physics-based dynamic rupture models capture the variability of earthquake slip in space and time and can account for the structural complexity inherent to subduction zones. Here we link tsunami generation, propagation, and coastal inundation with 3D earthquake dynamic rupture (DR) models initialized using a 2D seismo-thermo-mechanical geodynamic (SC) model simulating both subduction dynamics and seismic cycles. We analyze a total of 15 subduction-initialized 3D dynamic rupture-tsunami scenarios in which the tsunami source arises from the time-dependent co-seismic seafloor displacements with flat bathymetry and inundation on a linearly sloping beach. We first vary the location of the hypocenter to generate 12 distinct unilateral and bilateral propagating earthquake scenarios. Large-scale fault topography leads to localized up- or downdip propagating supershear rupture depending on hypocentral depth. Albeit dynamic earthquakes differ (rupture speed, peak slip-rate, fault slip, bimaterial effects), the effects of hypocentral depth (25–40 km) on tsunami dynamics are negligible. Lateral hypocenter variations lead to small effects such as delayed wave arrival of up to 100 s and differences in tsunami amplitude of up to 0.4 m at the coast. We next analyse inundation on a coastline with complex topo-bathymetry which increases tsunami wave amplitudes up to ≈1.5 m compared to a linearly sloping beach. Motivated by structural heterogeneity in subduction zones, we analyse a scenario with increased Poisson's ratio of ν = 0.3 which results in close to double the amount of shallow fault slip, ≈1.5 m higher vertical seafloor displacement, and a difference of up to ≈1.5 m in coastal tsunami amplitudes. Lastly, we model a dynamic rupture “tsunami earthquake” with low rupture velocity and low peak slip rates but twice as high tsunami potential energy. We triple fracture energy which again doubles the amount of shallow fault slip, but also causes a 2 m higher vertical seafloor uplift and the highest coastal tsunami amplitude (≈7.5 m) and inundation area compared to all other scenarios. Our mechanically consistent analysis for a generic megathrust setting can provide building blocks toward using physics-based dynamic rupture modeling in Probabilistic Tsunami Hazard Analysis.

Tsunami detection by GPS-derived ionospheric total electron content

To unravel the relationship between earthquake and tsunami using ionospheric total electron content (TEC) changes, we analyzed two Chilean tsunamigenic subduction earthquakes: the 2014 Pisagua Mw 8.1 and the 2015 Illapel Mw 8.3. During the Pisagua earthquake, the TEC changes were detected at the GPS sites located to the north and south of the earthquake epicenter, whereas during the Illapel earthquake, we registered the changes only in the northward direction. Tide-gauge sites mimicked the propagation direction of tsunami waves similar to the TEC change pattern during both earthquakes. The TEC changes were represented by three signals. The initial weaker signal correlated well with Acoustic Rayleigh wave (AWRayleigh), while the following stronger perturbation was interpreted to be caused by Acoustic Gravity wave (AGWepi) and Internal Gravity wave (IGWtsuna) induced by earthquakes and subsequent tsunamis respectively. Inevitably, TEC changes can be utilized to evaluate earthquake occurrence and tsunami propagation within a framework of multi-parameter early warning systems.

Tsunami evacuation times and routes to safe zones: a GIS-based approach to tsunami evacuation planning on the island of Stromboli, Italy

While a landslide at the volcanic island of Stromboli (Aeolian Islands, Italy) in December 2002 created a tsunami with a run-up of 10.9 m, two paroxysmal eruptions in the summer of 2019 caused a tsunami with an amplitude of 40 to 20 cm. All three events required rapid, spontaneous emergency evacuations of the beach zone as the time between tsunami generation and impact is around 4 min. These conditions thus require a special consideration of the issue of evacuation capabilities on the island in the event of a volcanogenic tsunami. The purpose of this paper is thus to (i) determine pedestrian evacuation times from high-risk coastal areas to safe zones, (ii) to assess building evacuation ease, and (iii) determine emergency evacuation plans (for buildings and coastal zones). For this purpose, we created a GIS-based risk analysis/mapping tool that also allowed macroscopic evacuation modelling. In our case, the high-risk zone to be evacuated involves an area extending to 10 m a.s.l. and involving 123 individual buildings over an area of 0.18 km2. The results show that 33% of the buildings can be evacuated in 4 min, and that a 10-min warning time is required for a complete and well-distributed evacuation whereby the population is evenly distributed between all evacuation exits to avoid the potential for congestion. Initial interviews of residents in the at-risk zone reveal a high level of awareness and a desire for personalized evacuation scenarios.

A first estimation of tsunami hazard of the Pacific coast of Costa Rica from local and distant seismogenic sources

Costa Rica has been affected by several local and distant tsunamis in the past, but the historical information is scarce and incomplete. Its Pacific coast stretches for over a thousand kilometers, and tsunami hazard has never been evaluated for its full extent. Numerical modeling of tsunami propagation and inundation is a useful tool to assess tsunami hazard, particularly in cases with limited historical information available. Here, we perform a first estimation of tsunami hazard for the Pacific coast of Costa Rica from seismogenic sources, by numerical propagation of 57 local and distant tsunamis to a depth of 20 m. The results of our study identified tsunami sources that are particularly threatening for Costa Rica and determined locations with higher tsunami hazard. For the analysis, the Pacific coast of Costa Rica was divided into segments and subsegments based on differences in continental slope morphology. Subsegments with higher tsunami heights were Southwest Nicoya Peninsula and West Osa Peninsula, and in a lesser extent North Guanacaste, North Nicoya Peninsula, and Central Pacific. Regions with long and gentle slopes and narrow continental shelf were affected by higher tsunami waves, due to more efficient tsunami energy transmission to the shelf and reduced energy loss while traveling through a narrow shelf. On the opposite, steeper continental slopes reflected most of the tsunami energy, causing smaller tsunami heights nearshore, regardless of the shelf width. Nevertheless, other effects played a major role, like curved coastlines that focused tsunami energy, wave refraction, interference, and trapped edge waves. Distant tsunamis dominated the threat, with tsunamis coming from the Tonga-Kermadec and the Colombia-Ecuador Trenches causing the greatest heights due to directivity, and arrival times of about 15 h and 75 min, respectively. Local tsunamis had short arrival times but a localized impact, mainly at the shoreline in front of the generation region but were also affected by tsunami focusing, wave refraction, and edge waves. Outer rise and Osa sources caused the lowest impact within local sources. These results provide a guide for emergency planners to prioritize coastal locations and tsunami sources for tsunami preparedness actions and warning protocols.

Propagation and amplification of meteotsunamis in multiple harbors along the eastern Yellow Sea coast

This study investigates the propagation and principal resonance characteristics of meteorological tsunamis (i.e., meteotsunamis) along the eastern Yellow Sea coast, which were anomalously strong in multiple harbors on April 25–26, 2008. Meteorological and sea level data were used to examine the link between atmospheric disturbances and meteotsunamis, and meteorological images were collected to estimate the propagation of atmospheric disturbances. Significant tsunami-like sea level oscillations were sequentially detected at the harbor tide gauges with increased spectral energy within broad period bands of less than 30 min, containing the fundamental period of each harbor. Meteorological parameters indicating the passage of a squall line, such as air pressure disturbances, wind disturbances, high rain rates, and lightning strikes, were also observed. The long ocean waves forced by the propagating squall line generated internal resonances, causing local amplification in multiple harbors. It appears that meteotsunami-induced harbor seiches were generated. Our results demonstrated that the pressure-forced meteotsunamis propagated toward the entrance of the harbors located on the propagation path, resulting in additional amplification by harbor resonance after the Proudman resonance amplifying the long waves in the open sea. The resonance characteristics favorable to additional amplification are the propagation of intense air pressure disturbances, harbors with large quality factors, and dominant period bands of the incoming long waves. The proposed resonance characteristics of specific sites can help in improving the accuracy of the current meteotsunami monitoring system in the Yellow Sea.

A numerical study of single N-type tsunami drawdown processes at a geophysical scale

Inundations by tsunamis have caused tremendous disasters on coasts all over the world. Consequently, the characteristics of tsunami runup have attracted public and scientific curiosity, which have led to a better understanding of the characteristics of tsunami evolution and runup. On the other hand, the drawdown of tsunamis has less attracted public and scientific interest. Thus, in this study, we investigate the drawdown processes of tsunamis at a geophysical scale. We simulate tsunami propagation and drawdown using a numerical model for fully nonlinear, weakly dispersive, rotational, and turbulent flow. Considering typical geophysical scales, we examine the effects of the amplitude, period, and shape of the incident wave, and bathymetric slope. The simulations show that the maximum drawdown of single leading-elevation N-wave (LEN) occurs prior to runup phase, whereas the maximum drawdown of single leading-depression N-wave (LDN) occurs after the runup phase. In addition, it is observed that the physical processes to induce drawdown of LDN- and LEN-type tsunamis are different from each other. Counterintuitively, the maximum drawdown depth of LEN can be greater than LDN tsunamis. Although the physical procedures are different, the maximum drawdown depths of both N-type tsunamis follow power functional relationships with the surf-similarity parameter ξ (Battjes, 1974). A noteworthy point is their power-law exponent o fξ: The numerical simulations under the geophysical scales result in that the ratio of maximum drawdown depth to incident tsunami wave amplitude is proportional to −ξ0.7 and −ξ−0.4 for which ξ<∼10 and 10<∼ξ<∼100, respectively, regardless of LDN or LEN. Based on this consistency, we propose empirical formulae to predict the maximum drawdown depth of single N-type tsunamis.

Theoretical study of the differential equation concept of tsunami waves using the leapfrog scheme

In this research work, tsunami wave propagation models and the underlying theory are examined through solving numerical wave-based partial differential equations using the leapfrog scheme. Following the wave physics theory, shallow water equations are explored for their basics and influential parameters; then, numerical methods are employed to solve said equations. As a result, the derivatives of shallow water equations for tsunami propagation modeling have been successfully formulated.

Accretionary wedge and oceanic crust thickness effect on surface deformation: Study case the Mentawai segment

Southern Sumatra forearc is classified as a compressional accretionary type. The existence of the accretionary wedge has a significant role in sediment deformation. This sediment deformation may contribute to generating higher tsunami generation. A two-dimensional crustal deformation modeling was performed to analyze the influence of the accretionary wedge. Furthermore, oceanic crust thickness variations are also simulated in this modeling as the incoming plate’s role in surface deformation is poorly understood. The crustal deformation modeling consists of two types of earthquake period: interseismic period and coseismic period. Various geometry features were applied for each earthquake period. The crustal deformation modeling itself is based on the finite element method. The result shows that there are different effects on the geometrical model being used. The pattern and amount of surface deformation also depend on at which the fault is activated. Extended geometry models such as three-dimensional modeling will be required for further study.

Modeling Tsunamis Generated by Submarine Landslides at Stromboli Volcano (Aeolian Islands, Italy): A Numerical Benchmark Study

We present a benchmark study aimed at identifying the most effective modeling approach for tsunami generation, propagation, and hazard in an active volcanic context, such as the island of Stromboli (Italy). We take as a reference scenario the 2002 landslide-generated tsunami event at Stromboli simulated to assess the relative sensitivity of numerical predictions to the landslide and the wave models, with our analysis limited to the submarine landslide case. Two numerical codes, at different levels of approximation, have been compared in this study: the NHWAVE three-dimensional non-hydrostatic model in sigma-coordinates and the Multilayer-HySEA model. In particular, different instances of Multilayer-HySEA with one or more vertical discretization layers, in hydrostatic and non-hydrostatic formulation and with different landslide models have been tested. Model results have been compared for the maximum runup along the shores of Stromboli village, and the waveform sampled at four proximal sites (two of them corresponding to the locations of the monitoring gauges, offshore the Sciara del Fuoco). Both rigid and deformable (granular) submarine landslide models, with volumes ranging from 7 to 25 million of cubic meters, have been used to trigger the water waves, with different physical descriptions of the mass movement. Close to the source, the maximum surface elevation and the resulting runup at the Stromboli village shores obtained with hydrostatic and non-hydrostatic models are similar. However, hydrostatic models overestimate (with respect to non-hydrostatic ones) the amplitude of the initial positive wave crest, whose height increases with the distance. Moreover, as expected, results indicate significant differences between the waveforms produced by the different models at proximal locations. The accurate modeling of near-field waveforms is particularly critical at Stromboli in the perspective of using the installed proximal sea-level gauges, together with numerical simulations, to characterize tsunami source in an early-warning system. We show that the use of non-hydrostatic models, coupled with a multilayer approach, allows a better description of the waveforms. However, the source description remains the most sensitive (and uncertain) aspect of the modeling. We finally show that non-hydrostatic models, such as Multilayer-HySEA, solved on accelerated GPU architectures, exhibit the optimal trade-off between accuracy and computational requirements, at least for the envisaged problem size and for what concerns the proximal wave field of tsunamis generated by volcano landslides. Their application and future developments are opening new avenues to tsunami early warning at Stromboli.

Constraints on the Slip Distribution of the 1938 MW 8.3 Alaska Peninsula Earthquake From Tsunami Modeling

AbstractWe simulated tsunami propagation for several scenario slip distributions for the 1938 MW 8.3 earthquake along the Alaska Peninsula and compared these to the observed records at Unalaska/Dutch Harbor and Sitka. The Sitka record is sensitive to the depth of slip but not the along‐strike location and is fit best by slip at shallow depth. The Unalaska record is sensitive mainly to the along‐strike location of slip and is fit best by slip that is concentrated in the eastern part of the presumed 1938 rupture zone. The tsunami data show that the actual 1938 earthquake rupture zone was likely ∼200 km in length or shorter and had no slip near the Shumagin Islands or in the 2020 Simeonof earthquake's rupture zone. The rupture models that best predict the 1938 tsunami lie within the region of high present day slip deficit inferred from GPS.

Anatomy of strike-slip fault tsunami genesis

Tsunami generation from earthquake-induced seafloor deformations has long been recognized as a major hazard to coastal areas. Strike-slip faulting has generally been considered insufficient for triggering large tsunamis, except through the generation of submarine landslides. Herein, we demonstrate that ground motions due to strike-slip earthquakes can contribute to the generation of large tsunamis (>1 m), under rather generic conditions. To this end, we developed a computational framework that integrates models for earthquake rupture dynamics with models of tsunami generation and propagation. The three-dimensional time-dependent vertical and horizontal ground motions from spontaneous dynamic rupture models are used to drive boundary motions in the tsunami model. Our results suggest that supershear ruptures propagating along strike-slip faults, traversing narrow and shallow bays, are prime candidates for tsunami generation. We show that dynamic focusing and the large horizontal displacements, characteristic of strike-slip earthquakes on long faults, are critical drivers for the tsunami hazard. These findings point to intrinsic mechanisms for sizable tsunami generation by strike-slip faulting, which do not require complex seismic sources, landslides, or complicated bathymetry. Furthermore, our model identifies three distinct phases in the tsunamic motion, an instantaneous dynamic phase, a lagging coseismic phase, and a postseismic phase, each of which may affect coastal areas differently. We conclude that near-source tsunami hazards and risk from strike-slip faulting need to be re-evaluated.