Local Tsunami Research Articles

Simulation of Tsunami Inundation for the Island of Martinique to Nearby Large Earthquakes

ABSTRACT In this article, we estimate the tsunami hazard in Martinique due to tsunamis generated by earthquakes associated with the Lesser Antilles subduction zone. Using a deterministic approach based on reliable earthquake scenarios, we use high-resolution bathymetric and topographic data to model tsunami propagation and inundation with Cornell Multi-grid Coupled Tsunami model. An extreme earthquake subduction scenario of magnitude Mw 8.0 is tested, and a further realistic scenario of lower magnitude Mw 7.5, thus of different tsunami frequency content, is also processed to test the possible appearance of bay resonances. We find that the western coast of the island is relatively sheltered, because it represents a shadow area to diffraction, in particular, for the major city of Fort de France. Because of its very gentle slope, the eastern coast is prone to numerous floodings with meter scale wave amplitudes; most of the inundated zones consist of mangroves and geological depressions t are naturally regularly flooded by tides or storm surges. Hence such areas are often not exploited, the mangroves being let in their natural state, enhancing the protection of the surrounding communities. However, some strategic inhabited areas are subject to severe inundation. Finally, comparing our results with studies of the 1755 Lisbon transoceanic tsunami reveals a tsunami hazard close to our local Mw 7.5 scenario. It suggests the possibility to generalize our local tsunami hazard assessment in Martinique to other tsunami contexts and enlarge its validity. This issue is crucial for minimizing the efforts and increasing the efficiency of tsunami preparedness.

High-Resolution Marine Seismic Imaging of the Seattle Fault Zone: Near-Surface Insights into Fault Zone Geometry, Quaternary Deformation, and Long-Term Evolution

ABSTRACTThe Seattle fault zone (SFZ) is a north-directed thrust fault system that underlies the greater Seattle metropolitan area. Evidence of past land level changes, landslides, liquefaction, and a local tsunami indicate that this 70-km-long fault system can host up to M 7–7.5 earthquakes. Both the geometry and earthquake recurrence of the SFZ are debated and surveys of the shallow subsurface have not yet been incorporated into deeper crustal-scale structural interpretations, especially where the SFZ cuts across marine portions of the Puget Lowland. Here we use a new high-resolution marine seismic reflection dataset to image fault-related deformation in Quaternary sediments and Tertiary bedrock throughout Puget Sound and Lake Washington. We use this perspective of shallow geology as a link between existing crustal-scale geophysical insights into fault geometry at depth and paleoseismological observations of faulting at the surface and propose a refined structural model for the SFZ. We interpret that our new seismic reflection data in the Rich Passage area of Puget Sound images evidence of an inactive, south-dipping strand of the SFZ, which is overprinted by Quaternary folding and slip along north-dipping backthrusts within the hanging wall of a blind, south-dipping fault located 6 km farther north. To explain these results, we propose that the SFZ is a normal sequence fault propagation fold that has stepped northward through time, and we show the plausibility of this model through trishear forward modeling. Growth strata and faulting imaged in Quaternary sediments in Lake Washington and Rich Passage are consistent with the spatial distribution of folding and backthrusting that occurred during an M 7–7.5 earthquake in A.D. 900–930, corroborating existing evidence that the SFZ has been active throughout the Quaternary.

Tsunami Hazard Assessment at Oeiras Municipality, Portugal

Portugal has had several large tsunamis in the past, yet Oeiras municipality has not implemented mitigation strategies and awareness to the general public, to the authors’ knowledge. In addition, Oeiras has 10 beaches that are very popular among residents and tourists, who can become at high risk of a potential tsunami if they do not evacuate from the low ground areas on time. Thus, the tsunami numerical model of the 1755 event was carried out to calculate the inundation, complemented with a field survey, in order to assess the tsunami evacuation conditions of the beaches. The results show the tsunami hits Oeiras municipality 26 to 36 min after the earthquake, inundating all the beaches. The local tsunami hazard classification is Low on 3 beaches, Moderate on 1 beach, High on 5 beaches, and Critical on 1 beach. In addition, there are no tsunami evacuation signs to guide the people to move to higher ground. Therefore, it is important to conduct mitigation strategies to avoid and reduce fatalities in a future tsunami.

Coastal Environmental Impact of Geohazards in the Area of the Habibas Islands (Western Algeria, Alboran): Insights from GIS-Analysis and Remote Sensing

Algerian coastal areas in the southern part of the western Mediterranean Sea are prone to geohazards such as tsunami waves, storm surges, earthquakes, submarine mass movements, and volcanism. Located in the Gulf of Oran, the Habibas Archipelago is a well-preserved bio-environment where fauna and flora are unique. This region is nevertheless a zone where marine traffic (oil) and oil ports pose a threat to environmental offshore pollution. This study is focused on submarine mass movements and their potential to cause local tsunami waves. Digital Elevation Model (DEM) data and the DEM-derived morphometric maps support these investigations being integrated into a GeoInformation System (GIS). Bathymetric data of the western Mediterranean Sea are used to derive causal factors that influence the susceptibility to submarine mass movements. Sentinel 2, Landsat 8, and Sentinel 1 radar images help to identify coastal areas prone to landslides and the coast-near structural pattern. By integrating data collected from the literature and maps (geology, tectonics, earthquakes, mass movements) into a GeoInformationSystem (GIS) and by using remote sensing analysis, it might be possible to derive more precisely in the case of submarine landslides and turbidity currents in the which direction potential tsunami waves caused by these mass movements might be focused and directed.

Dynamic off-fault failure and tsunamigenesis at strike-slip restraining bends: Fully-coupled models of dynamic rupture, ocean acoustic waves, and tsunami in a shallow bay

Inelastic off-fault deformation can lead to large tsunamigenesis in different tectonic settings. Here a mechanism for tsunami generation by strike-slip earthquakes that involves dynamic off-fault failure at restraining bends is presented. Dynamic rupture on a vertical strike-slip fault is modeled with undrained inelastic off-fault response incorporated by the Drucker-Prager yield criterion. I show that in a local transpressive stress regime dynamic off-fault failure at restraining bends produces significantly larger and more localized surface uplift than is produced by purely elastic dislocation models, resulting in a positive flower and coseismic pop-up structure. The larger uplift is due to frictional sliding with a thrust component on conjugate microfractures, modeled by inelastic deformation. The short-wavelength inelastic uplift, largely controlled by bend size, is shown to generate localized tsunami efficiently in a shallow bay by fully coupling dynamic rupture, ocean acoustic waves, and tsunami. Fully-coupled models also indicate that supershear rupture on a vertical planar strike-slip fault does not generate large tsunami as the large kinetic energy of supershear rupture is carried away by ocean acoustic waves. Dynamic off-fault failure at fault complexities, such as restraining bends and compressional stepovers, may need be urgently incorporated in the current tsunami hazard assessments in strike-slip environments.

Upper-plate structure and tsunamigenic faults near the Kodiak Islands, Alaska, USA

AbstractThe Kodiak Islands lie near the southern terminus of the 1964 Great Alaska earthquake rupture area and within the Kodiak subduction zone segment. Both local and trans-Pacific tsunamis were generated during this devastating megathrust event, but the local tsunami source region and the causative faults are poorly understood. We provide an updated view of the tsunami and earthquake hazard for the Kodiak Islands region through tsunami modeling and geophysical data analysis. Using seismic and bathymetric data, we characterize a regionally extensive seafloor lineament related to the Kodiak shelf fault zone, with focused uplift along a 50-km-long portion of the newly named Ugak fault as the most likely source of the local Kodiak Islands tsunami in 1964. We present evidence of Holocene motion along the Albatross Banks fault zone, but we suggest that this fault did not produce a tsunami in 1964. We relate major structural boundaries to active forearc splay faults, where tectonic uplift is collocated with gravity lineations. Differences in interseismic locking, seismicity rates, and potential field signatures argue for different stress conditions at depth near presumed segment boundaries. We find that the Kodiak segment boundaries have a clear geophysical expression and are linked to upper-plate structure and splay faulting. The tsunamigenic fault hazard is higher for the Kodiak shelf fault zone when compared to the nearby Albatross Banks fault zone, suggesting short wave travel paths and little tsunami warning time for nearby communities.

Perceptions of tsunami susceptibility and self-efficacy among adolescents in Indonesia: The influence of gender, religion, location, age, hazard information source, and past experience

Perceptions of tsunami susceptibility and self-efficacy among adolescents in Indonesia: The influence of gender, religion, location, age, hazard information source, and past experience.The densely populated Indonesian archipelago is highly vulnerable to earthquakes and tsunamis. Behavioral theory suggests perceived susceptibility and perceived self-efficacy are positively correlated with preventive behaviors. We surveyed adolescents (N = 2386) in tsunami-vulnerable coastal areas of Java, Bali, Lombok, and Sumba Indonesia. We conducted a stepwise logistic regression analysis of perceived tsunami susceptibility and self-efficacy. Explanatory variables included sex, age, religion, island of residence, hazard information source, previous participation in tsunami evacuation drills, and personal tsunami experience. The majority (60.6%) of participants believed that they were susceptible to an earthquake. About half of participants believed they were susceptible to a tsunami (49.8%) and that they would be able to save themselves if a tsunami occurred (48.5%). Individuals residing in Java, females, Muslims, older participants, and those who received tsunami information from the Internet and Indonesia's regional governmental disaster management agency (BPBD) were significantly more likely to feel susceptible to a tsunami. Catholics, Protestants, individuals living in Java, those who participated in past tsunami evacuation drills, and those with personal tsunami experience had significantly higher perceived self-efficacy. Females and participants who received hazard-related information from the Internet and BPBD had significantly lower perceived self-efficacy. Our study highlights the importance of providing culturally competent information about local tsunami risk to vulnerable locations through a variety of communication channels. Identifying cultural, economic, and religious barriers is important when developing educational interventions. Efficacy perceptions should be improved through education about immediate self-evacuation after observation of tsunami natural warning signs, construction of vertical evacuation structures in coastal areas, and encouraging participation in tsunami evacuation drills.

Analysis of Faster-Than-Real-Time (FTRT) Tsunami Simulations for the Spanish Tsunami Warning System for the Atlantic

Real-time local tsunami warnings embody uncertainty from unknowns in the source definition within the first minutes after the tsunami generates. In general, Tsunami Warning Systems (TWS) provide a quick estimate for tsunami action from deterministic simulations of a single event. In this study, variability in tsunami source parameters has been included by running 135 tsunami simulations; besides this, four different computational domains in the northeastern Atlantic ocean have been considered, resulting in 540 simulations associated with a single event. This was done for tsunamis generated by earthquakes in the Gulf of Cadiz with impact in the western Iberian peninsula and the Canary Islands. A first answer is provided after one minute, and 7 min are required to perform all the simulations in the four computational domains. The fast computation allows alert levels all along the coast to be incorporated into the Spanish National Tsunami Early Warning System. The main findings are that the use of a set of scenarios that account for the uncertainty in source parameters can produce higher tsunami warnings in certain coastal areas than those obtained from a single deterministic reference scenario. Therefore, this work shows that considering uncertainties in tsunami source parameters helps to avoid possible tsunami warning level underestimations. Furthermore, this study demonstrates that this is possible to do in real time in an actual TWS with the use of high-performance computing resources.

Tsunami or storm deposit? A late Holocene sedimentary record from Swamp Bay, Rangitoto ki te Tonga/D’Urville Island, Aotearoa – New Zealand

ABSTRACT Informed by Māori oral histories that refer to past catastrophic marine inundations, multi-proxy analysis of stratigraphic records from Swamp Bay, Rangitoto ki te Tonga (D’Urville Island) shows evidence of an anomalous deposit extending some 160 m inland. The deposit includes two distinct lithofacies. The lower sand unit is inferred to have been transported from the marine environment, with corresponding increases in the percentages of benthic marine and brackish–marine diatoms, and geochemical properties indicative of sudden changes in environmental conditions. Radiocarbon dating indicates the deposit formation is less than 402 yrs BP, and pollen indicates it is unlikely to be younger than 1870 CE. Core stratigraphy age models and co-seismic chronologies point to the marine unit most likely being emplaced by tsunami transport associated with rupture of the Wairarapa Fault in 1855 CE. The overlying unit of gravel and silt is inferred to be fluvial deposit and slope-wash from the surrounding hills, loosened by ground-shaking following the earthquake. These findings indicate the 1855 CE earthquake may have been more complex than previously thought and, or, available tsunami modelling does not fully capture the local complexities in bathymetry and topography that can cause hazardous and localized tsunami amplification in embayments like Swamp Bay.

Automated Approaches for Capturing Localized Tsunami Response—Application to the French Coastlines

AbstractLocal bathymetry and onshore features can have a substantial effect on the spatial variability of the hazard from an incoming tsunami. In a warning context, being able to provide localized tsunami forecasts at strategic locations would therefore help mitigate the damage. Despite the recent advancements in computing powers and the development of highly efficient tsunami codes, capturing this local variability can oftentimes be infeasible in a warning setting. Traditional high‐resolution simulations which can capture these localized effects are often too costly to run “on‐the‐fly.” Alternative approaches that capture the localized response to an incoming tsunami, which are based upon using the maximum wave heights from a computationally cheap regional forecast, are developed here. These alternative approaches are envisaged to aid in a warning center's ability at providing extremely rapid localized forecasts. The approaches focus upon two different methods: transfer functions and machine learning techniques. The transfer function is based upon a recent extension to the established Green's Law. The extended version introduces local amplification parameters, with the aim of capturing the neglected localized effects. An automated approach which optimizes for these local amplification parameters is outlined and the performance of the transfer function is explored. A machine learning model is also trained and used to predict the localized tsunami hazard. Its performance is compared to the extended Green's Law approach for a site along the French coast. These developed methods showcase promising techniques that a tsunami warning center could use to provide high‐resolution warnings.

Occurrence of Local Tsunamis Along the Eastern Coast of the Korean Peninsula Based on Numerical Modeling of Historical Earthquakes

Korean historical literature records a major offshore earthquake with an associated tsunami in the East Sea of Korea in 1681. The event also generated strong ground motion and landslides over the Korean Peninsula. This study examined the occurrence and characteristics of the reported tsunami along the eastern coast of the peninsula using numerical modeling of tsunami propagation from submarine faults identified in a recently compiled marine fault map. Results from some scenarios indicated runup heights in good agreement with descriptions in historical records. We also examined the time required for tsunamis to travel from the causative faults to vulnerable areas along the eastern coast under various scenarios. Our results successfully hindcast the occurrence and effects of local tsunamis in the historical literature and have important implications for assessing tsunami hazard and risk for coastal areas of the Korean Peninsula.

Tsunami hazard in Lombok and Bali, Indonesia, due to the Flores back-arc thrust

Abstract. The tsunami hazard posed by the Flores back-arc thrust, which runs along the northern coast of the islands of Bali and Lombok, Indonesia, is poorly studied compared to the Sunda Megathrust, situated ∼250 km to the south of the islands. However, the 2018 Lombok earthquake sequence demonstrated the seismic potential of the western Flores Thrust when a fault ramp beneath the island of Lombok ruptured in two Mw 6.9 earthquakes. Although the uplift in these events mostly occurred below land, the sequence still generated local tsunamis along the northern coast of Lombok. Historical records show that the Flores fault system in the Lombok and Bali region has generated at least six ≥Ms 6.5 tsunamigenic earthquakes since 1800 CE. Hence, it is important to assess the possible tsunami hazard represented by this fault system. Here, we focus on the submarine fault segment located between the islands of Lombok and Bali (below the Lombok Strait). We assess modeled tsunami patterns generated by fault slip in six earthquake scenarios (slip of 1–5 m, representing Mw 7.2–7.9+) using deterministic modeling, with a focus on impacts on the capital cities of Mataram, Lombok, and Denpasar, Bali, which lie on the coasts facing the strait. We use a geologically constrained earthquake model informed by the Lombok earthquake sequence, together with a high-resolution bathymetry dataset developed by combining direct measurements from the General Bathymetric Chart of the Oceans (GEBCO) with sounding measurements from the official nautical charts for Indonesia. Our results show that fault rupture in this region could trigger a tsunami reaching Mataram in <9 min and Denpasar in ∼ 23–27 min, with multiple waves. For an earthquake with 3–5 m of coseismic slip, Mataram and Denpasar experience maximum wave heights of ∼ 1.6–2.7 and ∼ 0.6–1.4 m, respectively. Furthermore, our earthquake models indicate that both cities would experience coseismic subsidence of 20–40 cm, exacerbating their exposure to both the tsunami and other coastal hazards. Overall, Mataram is more exposed than Denpasar to high tsunami waves arriving quickly from the fault source. To understand how a tsunami would affect Mataram, we model the associated inundation using the 5 m slip model and show that Mataram is inundated ∼ 55–140 m inland along the northern coast and ∼230 m along the southern coast, with maximum flow depths of ∼ 2–3 m. Our study highlights that the early tsunami arrival in Mataram, Lombok, gives little time for residents to evacuate. Raising their awareness about the potential for locally generated tsunamis and the need for evacuation plans is important to help them respond immediately after experiencing strong ground shaking.

Preliminary Observations and Impact in Japan of the Tsunami Caused by the Tonga Volcanic Eruption on January 15, 2022

The tsunami caused by the Tonga submarine volcanic eruption that occurred at 13:15 Japan Time (JST) on January 15, 2022, exposed a blind spot in Japan’s tsunami monitoring and warning system, which was established in 1952 for local tsunamis and expanded to distant tsunamis after the 1960 Chile tsunami. This paper summarizes how the warning system responded to the unprecedented tsunami, the actual evacuation process, and the damage it caused in Japan. Initially, the tsunami from the volcanic eruption was expected to arrive at approximately midnight with amplitudes of less than 20 cm. However, a series of short waves arrived at approximately 21:00, a few hours earlier than expected. The early arrival of these sea waves coincided with a rapid increase in atmospheric pressure; then, the short-period component was predominant, and the wave height was amplified while forming wave groups. After a 1.2 m tsunami was observed in Amami City in southern Japan at 23:55 JST, the Japan Meteorological Agency issued a tsunami warning/advisory. The tsunami continued, and all advisories were cleared at 14:00 JST on January 16. Information about this tsunami and the response to it are summarized here, including the characteristics and issues of the actual tsunami evacuation situation in each region. There were no casualties, but the issues that emerged included difficulty evacuating on a winter night and traffic congestion due to evacuation by car and under the conditions of the COVID-19 pandemic. In the coastal area, damage to fishing boats and aquaculture facilities was reported due to the flow of the tsunami. In addition, damage to aquaculture facilities, including those producing oysters, scallops, seaweed and other marine products, decreased the supply of marine products, and the economic impact is likely to increase in the future.

Local tsunamigenic sources in Greece, identified by pattern recognition

This study is an attempt to determine potential tsunamigenic morphostructural nodes in Greece using pattern recognition algorithms. The earthquakes that have produced local tsunamis in the region were confined to morphostructural nodes whose locations were found by morphostructural zoning. The recognition problem consisted in separating all nodes in the region into the tsunamigenic class and the non-tsunamigenic class based mainly on the geomorphologic parameters of the nodes. The data on tsunamigenic earthquakes in Greece for training the Cora-3 algorithm were taken from the GHTD global historical catalog of tsunamigenic events (http://www.ngdc.noaa.gov/hazard/tsu_db.shtml). The recognition procedure resulted in determining 27 tsunamigenic nodes, with most of these being situated in the southern tip of the Peloponnese Peninsula, as well as in the gulfs of Corinth and Patras. Three tsunamigenic nodes were identified in the area of the Malian Gulf on the Aegean coast of Greece. According to the relevant literature, most local tsunamis in Greece were initiated by submarine slides and slumps due to earthquakes. According to the characteristic geomorphologic features derived in this study, the tsunamigenic nodes are situated in settings of contrasting relief characterized by steep slopes. This favors submarine landslides when subjected to earthquake excitation. The results reported in this paper form a basis for developing a methodology to be used in long-term tsunami hazard assessment, supplying information on local potential tsunamigenic sources required for tsunami regionalization of coastal areas in Greece.

Reconstructing the 26 June 1917 Samoa Tsunami Disaster

The 1917 Samoa tsunamigenic earthquake is the largest historical event to impact this region. Over a century later, little is known about the tsunami magnitude and its implications for modern society. This study reconstructs the 1917 tsunami to understand its hazard characteristics in the Samoan region and assesses the risk implications of tsunamis sourced from different locations along the subduction zone bend of the Northern Tonga Trench (NTT). We model the event from its origin to produce outputs of tsunami inundation extent and depth at spatially flexible grid resolution, which are validated using available runup observations and Apia harbour tide gauge records. We then combine the inundation model with digital distributions of buildings to produce exposure metrics for evaluating the likely impacts on present-day coastal assets and populations if a similar tsunami were to occur. Results exhibit recorded and modelled wave arrival time discrepancies in Apia harbour of between 30–40 min, with runup underestimated in southeast Upolu Island compared with the rest of the country. These differences could reflect complexities in the tsunami source mechanism that are not represented in our modelling and require further investigation. Nevertheless, our findings suggest that if a characteristic 1917-type event were to occur again, approximately 71% of exposed people would reside in Savai’i. Overall, this study provides the first detailed inundation model of the 1917 tsunami that supports an appreciation of the regional risk to local tsunamis sourced at the subduction zone bend of the NTT in Samoa.

Paleo Isobaths in 3D Seismic Exploration Data Uncover Submerged Shorelines From Glacial Lowstands: A Case Study From the Levant Basin

Modern petroleum exploration extracts 3D volumes of seismic data where certain curves can be drawn delimiting stratigraphic horizons. Such curves hold a promise as piercings for identifying tectonic offsets in 3D. Pinchout points on vertical sections connect with adjacent sections to form contours in 3D. Such a contour, showing quasi-uniform depth, may be considered a paleo-isobath. Here we focus on pinchout paleo-isobaths in the western shores of the Levant that might record ∼120 m drop in sea level at the peak of late Quaternary glacials. We identified a pinchout isobath, ∼15 km offshore, ∼140 m below sea level. Water depth averages ∼90 m, and sediment cover averages ∼45 m. Allowing for isostatic adjustment, this is compatible with eustatic levels of the last two glacial maxima. We hypothesize that the contour mapped is closely related to the shoreline of one of the last glacial maxima. The pinchout pattern is continuous for ∼25 km in the southern reaches of the survey area, at depths of 137 ± 2.5 m, an isobath within the observational uncertainty. The isobath is lost for ∼10 km in the central portion of the survey, north of which a slightly deeper isobath reappears for 7 km, until it disappears approaching a bathymetric trough. The deeper pinchout isobath reappears in the northernmost section of the survey, where it deepens by an average of 5–6 m relative to the southern part (from 137 m to 142 m). The deepening of the pinchout contour is consistent with massive sliding underlying the trough. Sliding here has been attributed to sediment load or salt tectonics, and has been recently associated with a local tsunami dating 9.6 ± 0.3 ka. Recent work relocated the deepest earthquakes on the Levant southern shelf (depths circa 30 km) to the trough, with epicenters coinciding with the boundary faults. This may indicate an active deep-seated tectonic feature. Expressions of the contour outside the survey area will offer tests to our paleo-shoreline hypothesis. Additional pinchout isobaths and pinchout contours associated with earlier lowstands will help constrain tectonic rates as well as glacial eustatic levels and hydro-isostatic effects, with potential regional and global applications.

Parallel density scanned adaptive Kriging to improve local tsunami hazard assessment for coastal infrastructures

Seismic Probabilistic Tsunami Hazard Assessment (SPTHA) is a framework for calculating the probability that seismically induced tsunami waves exceed a specific threshold height, over a given time span and a specific region (i.e. regional SPTHA) or site (i.e. local SPTHA). To account for the uncertainty of the possible sources, SPTHA must integrate the results of a large number of computationally demanding tsunami simulationsIn this work, we innovatively use Parallel density scanned Adaptive Kriging (P-ds AK) to overcome the computational efficiency challenge of local SPTHA within a framework that consists in modeling/retrieving the full spectrum of possible earthquake triggering events at the regional level, filtering sources not relevant for the target, adopting a clustering procedure to select “representative scenarios” for inundation modeling, and, finally, adopt P-ds AK to identify the clusters centroids that most influence the hazard intensity (i.e., wave height) in the areas of interest.This approach is applied in the area of the oil refinery located in Milazzo (Italy). The application shows a consistent reduction of the number of high-resolution tsunami simulations required for the evaluation of the hazard curves over a set of inland Point of Interest (PoIs), either concentrated in one specific area or distributed along the coast.

Iceberg-Induced Tsunamis Near Dålk Glacier, Antarctica

AbstractA unique local tsunami had a very large impact on the coastal stations near Dalk Glacier; this kind of tsunami is related to iceberg activity. To provide a reference for tsunami warning and...

Numerical study of waves generated during iceberg calving in sliding mode

The calving of large-scale icebergs into the sea can generate a local tsunami that may threaten human lives or passing ships. A smoothed particle hydrodynamics model of this rigid-body–fluid system was established to simulate the sliding mode of the detaching iceberg and the waves generated during its collapse. The generation and evolution processes, and the near flow-field characteristics of the waves are analyzed and presented in detail. The simulation results show that the waves have different features from impulse waves generated in landslides. Waves generated in iceberg calving can generate not only a huge leading wave but also a notable second wave that under certain conditions may have an amplitude comparable or even larger than that of its leading wave. A criterion based on the Froude number and a combined dimensionless number formed from the aspect ratio and the relative height of the iceberg are established to distinguish the leading and second waves. Using 125 cases of simulations of these waves for different conditions, two empirical equations for quantifying the amplitudes of both waves in terms of the Froude number, aspect ratio, and relative iceberg length are given that may be of practical help in hazard assessments from iceberg calving.

Characterization of fault plane and coseismic slip for the 2 May 2020, <i>M</i><sub>w</sub> 6.6 Cretan Passage earthquake from tide gauge tsunami data and moment tensor solutions

Abstract. We present a source solution for the tsunami generated by the Mw 6.6 earthquake that occurred on 2 May 2020, about 80 km offshore south of Crete, in the Cretan Passage, on the shallow portion of the Hellenic Arc subduction zone (HASZ). The tide gauges recorded this local tsunami on the southern coast of Crete and Kasos island. We used Crete tsunami observations to constrain the geometry and orientation of the causative fault, the rupture mechanism, and the slip amount. We first modelled an ensemble of synthetic tsunami waveforms at the tide gauge locations, produced for a range of earthquake parameter values as constrained by some of the available moment tensor solutions. We allow for both a splay and a back-thrust fault, corresponding to the two nodal planes of the moment tensor solution. We then measured the misfit between the synthetic and the Ierapetra observed marigram for each source parameter set. Our results identify the shallow, steeply dipping back-thrust fault as the one producing the lowest misfit to the tsunami data. However, a rupture on a lower angle fault, possibly a splay fault, with a sinistral component due to the oblique convergence on this segment of the HASZ, cannot be completely ruled out. This earthquake reminds us that the uncertainty regarding potential earthquake mechanisms at a specific location remains quite significant. In this case, for example, it is not possible to anticipate if the next event will be one occurring on the subduction interface, on a splay fault, or on a back-thrust, which seems the most likely for the event under investigation. This circumstance bears important consequences because back-thrust and splay faults might enhance the tsunamigenic potential with respect to the subduction interface due to their steeper dip. Then, these results are relevant for tsunami forecasting in the framework of both the long-term hazard assessment and the early warning systems.