Local Tsunami Research Articles

Forearc crustal faults as tsunami sources in the upper plate of the Lesser Antilles subduction zone: the case study of the Morne Piton fault system

Abstract. In this study, alternatively to the megathrust, we identify upper-plate normal faults orthogonal to the trench as a possible tsunami source along the Lesser Antilles subduction zone. The Morne Piton fault system is such a trench-perpendicular upper crustal fault at the latitude of Guadeloupe. By means of seismic reflection, high-resolution bathymetry, remotely operated vehicle (ROV) imaging and dating, we reassess the slip rate of the Morne Piton fault since 7 Ma, i.e., its inception, and quantify an average rate of 0.25 mm yr−1 since ca. 1.2 Ma. This result divides by two previous estimations, increases the earthquake time recurrence and lowers the associated hazard. The ROV dive revealed a metric scarp with striae at the toe of the Morne Piton fault system, suggesting a recent fault rupture. We estimate a fault rupture area of ∼ 450–675 km2 and then a magnitude range for a maximum seismic event around Mw 6.5 ± 0.5, making this fault potentially tsunamigenic as the nearby Les Saintes fault responsible for a tsunami following the 2004 Mw 6.3 earthquake. Consequently, we simulate a multi-segment tsunami model representative of a worst-case scenario if all the identified Morne Piton fault segments ruptured together. Our model provides clues for the potential impact of local tsunamis on the surrounding coastal area as well as for local bathymetric controls on tsunami propagation. We illustrate that (i) shallow-water plateaus act as secondary sources and are responsible for a wrapping of the tsunami waves around the island of Marie-Galante; (ii) canyons indenting the shallow-water plateau slope break focus and enhance the wave height in front of the most touristic and populated town of the island; and (iii) the resonance phenomenon is observed within the Les Saintes archipelago, showing that the waves' frequency content is able to perturb the sea level for many hours after the seismic rupture.

Tsunami risk perception of the touristic population of Stromboli Island: towards effective risk communication strategies

AbstractThis study focuses on the risks that tourists would face during a tsunami on the island of Stromboli and discusses how to best inform and prepare them. Tsunamis affect coastal regions, where many of these are leisure destinations for tourists who often don’t have adequate knowledge of the region's risks. Due to their proximity to the affected areas, near-source or local tsunamis usually allow for a limited warning time, posing great challenges to the planning of effective risk mitigation action. Furthermore, tourist populations have a particular significance in studies on risk perception, since their needs intersect with those of the local population and must be taken into account. To gather key knowledge for developing robust risk communication strategies, a survey (n = 699) was conducted between July and October 2023 to assess tourists' risk perception and preparedness. The findings indicate that tourists often misdescribe tsunamis, leading to underestimation of the security threats posed by smaller events and revealing shortcomings in current communication approaches. Given the tourism industry practices on the island, effective communication strategies for tourists should prioritize providing comprehensive information within the first 24 h of their arrival. Furthermore, given the high percentage of tourists who visit the island for a few hours and within certain time slots, we invite the authorities to provide this information before disembarking on the island.

Characterization of Underwater Landslides in Krui Waters, Lampung-Indonesia using Shallow Seismic and Sonar Data

Abstract Krui Waters, Lampung, Indonesia, is an area that has the potential for a tsunami disaster. Local tsunamis can be caused by underwater landslides owing to ground movement and gravitational forces. Imaging underwater conditions using sonar and shallow seismic systems is an interesting research topic for geological disaster researchers. Underwater landslides are very important for disaster mitigation, especially for tsunami prediction. This research aims to identify the characteristics of underwater landslides around Krui Waters, Lampung, Indonesia, using imaging analysis methods from sonar data and a sub-bottom profiler (SBP). The underwater landslide phenomenon in this area is still not known in detail, and therefore requires further research. All data were obtained from the results of hydrographic, geological, and geophysical surveys of RV Baruna Jaya IV in 2020. The sonar data shows surface characteristics such as the presence of Furrows (Gravel Waves), Cobble (Boulder), as well as Canyons and landslides or mass movements rocks. SBP data show the characteristics of the seabed in the form of a canyon with a slope greater than 160. Finally, the morphological characteristics and features obtained could possibly be a potential source of local tsunamis owing to the high slope.

Geohazard features of the Tyrrhenian Calabria

ABSTRACT This paper accompanies the Maps of Geohazard features of the Cilento and the Calabro-Tyrrhenian continental margin in the southern Tyrrhenian Sea (Italy). The main geohazard-related features were derived from extensive seafloor mapping through the collection of high-resolution multibeam data acquired during several oceanographic cruises. They encompass many fluids seepage features, fault scarps, landslides scars, gullies, channels, and canyons. Hazards related to coastal landslides and shelf-indenting canyons are very high in these sectors (especially in southern Calabria) due to active seismicity coupled with rapid uplift, high sedimentation rates and narrow or totally absent continental shelf, thus promoting a direct connection between steep slopes and coastal areas. In this setting, mass-wasting features can directly impact coastal or submarine infrastructures or indirectly create local tsunami waves, as observed in historical times. Moreover, this physiographic setting of the margin facilitates the transfer of marine litter toward deep-sea areas.

The Impact of the Three-Dimensional Structure of a Subduction Zone on Time-dependent Crustal Deformation Measured by HR-GNSS

Accurately modeling time-dependent coseismic crustal deformation as observed on high-rate Global Navigation Satellite System (HR-GNSS) lends insight into earthquake source processes and improves local earthquake and tsunami early warning algorithms. Currently, time-dependent crustal deformation modeling relies most frequently on simplified 1D radially symmetric Earth models. However, for shallow subduction zone earthquakes, even low-frequency shaking is likely affected by the many strongly heterogeneous structures such as the subducting slab, mantle wedge, and the overlying crustal structure. We demonstrate that including 3D structure improves the estimation of key features of coseismic HR-GNSS time series, such as the peak ground displacement (PGD), the time to PGD (tPGD), static displacements (SD), and waveform cross-correlation values. We computed synthetic 1D and 3D, 0.25 Hz and 0.5 Hz waveforms at HR-GNSS stations for four M7.3+ earthquakes in Japan using MudPy and SW4, respectively. From these synthetics, we computed intensity-measure residuals between the synthetic and observed GNSS waveforms. Comparing 1D and 3D residuals, we observed that the 3D simulations show better fits to the PGD and SD in the observed waveforms than the 1D simulations for both 0.25 Hz and 0.5 Hz simulations. We find that the reduction in PGD residuals in the 3D simulations is a combined effect of both shallow and deep 3D structures; hence incorporating only the upper 30 km of 3D structure will still improve the fit to the observed PGD values. Our results demonstrate that 3D simulations significantly improve models of GNSS waveform characteristics and will not only help understand the underlying processes, but also improve local tsunami warning.

Repeated Coseismic Uplift of Coastal Lagoons Above the Patton Bay Splay Fault System, Montague Island, Alaska, USA

AbstractCoseismic slip on the Patton Bay splay fault system during the 1964 Mw 9.2 Great Alaska Earthquake contributed to local tsunami generation and vertically uplifted shorelines as much as 11 m on Montague Island in Prince William Sound (PWS). Sudden uplift of 3.7–4.3 m caused coastal lagoons along the island's northwestern coast to gradually drain. The resulting change in depositional environment from marine lagoon to freshwater muskeg created a sharp, laterally continuous stratigraphic contact between silt and overlying peat. Here, we characterize the geomorphology, sedimentology, and diatom ecology across the 1964 earthquake contact and three similar prehistoric contacts within the stratigraphy of the Hidden Lagoons locality. We find that the contacts signal instances of abrupt coastal uplift that, within error, overlap the timing of independently constrained megathrust earthquakes in PWS—1964 Common Era, 760–870 yr BP, 2500–2700 yr BP, and 4120–4500 yr BP. Changes in fossil diatom assemblages across the inferred prehistoric earthquake contacts reflect ecological shifts consistent with repeated draining of a lagoon system caused by >3 m of coseismic uplift. Our observations provide evidence for four instances of combined megathrust‐splay fault ruptures that have occurred in the past ∼4,200 years in PWS. The possibility that 1964‐style combined megathrust‐splay fault ruptures may have repeated in the past warrants their consideration in future seismic and tsunami hazards assessments.

Small-Scale Experimental Evidence On The Use Of Date Palm Forest To Mitigate Tsunami In The Arabian Sea

Because of the multi-scale benefits, ecosystem-based disaster risk reduction (Eco-DRR) has received much attention in coastal disaster mitigation. Coastal forests are considered a sustainable and economical solution to mitigate inundations from tsunamis. Owing to the rare occurrence of tsunamis and reported local tsunami heights being small, the coastal forests are a potential solution to protect from tsunamis in the Arabian Sea. The potential of date palm trees to mitigate tsunami inundations was investigated in an experimental study. The experiments were conducted at a geometric scale of 1:100 with the Froude-Cauchy similitudes. It found that the canopy of the tree played a key role in flow energy reduction. If the tsunami height was higher than the canopy height a significant tsunami depth was reduced behind the forest compared to the case that the tsunami height was lower than the canopy height. The highest percentage reduction in the maximum flow depth behind the forest was 37% for the forest length of 180 m and tsunami height of 7 m.

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.

Origins of the Tsunami Following the 2023 Turkey–Syria Earthquake

AbstractOn 6 February 2023, a local tsunami was recorded in the southeastern Mediterranean Sea following the Mw 7.7 Turkey–Syria inland strike‐slip earthquake. Due to the lack of underwater observation, the tsunami generation mechanism remains mysterious. To understand the source mechanisms, we analyzed the tsunami waveforms of four nearby tide gauges and located possible sources using a backward tsunami ray tracing approach. We then conducted forward numerical modelings for a range of possible source parameters. We show that there were probably two tsunami sources, inside and outside Iskenderun Bay, which may be related to thick coastal sediments. A source inside the Bay with a characteristic length of 7 km produced dominant periods of 10–30 min with negative initial motion, possibly generated by a landslide. Another source of 6 km length outside the Bay produced dominant periods of 2–10 min with positive initial motions, possibly related with liquefaction.

Scenario-Based Hazard Assessment of Local Tsunami for Coastal Areas: A Case Study of Xiamen City, Fujian Province, China

In this study, three worst-case credible tsunamigenic scenarios (Mw8.0) from Xiamen fault 1 (XF 1), Xiamen fault 2 (XF 2) and Xiamen fault 3 (XF 3) located off the coast of Xiamen were selected to assess the local tsunami hazard for Xiamen city, Fujian province, China. The GeoClaw model was utilized to compute the propagation and inundation of the tsunami for each scenario. The simulation results show that local tsunamis from XF 1–3 hit Xiamen within 1.5 h of earthquakes. The highest level of tsunami hazard in Xiamen is level II, which corresponds to an inundation depth ranging from 1.2 to 3.0 m. The areas with tsunami hazard level II in each scenario are primarily concentrated in the coastal areas of southern Haicang district and eastern Siming district, which are in the primary propagation direction of the tsunami. Since XF 2 and XF 3 are aligned almost parallel to the coastline of Xiamen, local tsunamis from XF 2 and XF 3 could cause more serious hazards to the coastal areas of Xiamen city. This work provides a typical case for researchers to understand the local tsunami hazard assessment for coastal cities. The research results can provide scientific references for the development of tsunami hazard assessment and early warning systems for coastal cities in southeastern China.

Modeling non-structural strategies to reduce pedestrian evacuation times for mitigating local tsunami threats in Guam

Reducing the potential for loss of life from local tsunamis is challenging for emergency managers given the need for self-protective behavior of at-risk individuals within brief windows of time to evacuate. There has been considerable attention paid to discussing the use of tsunami vertical-evacuation structures for areas where there may be insufficient time to evacuate. This strategy may not be feasible or needed for at-risk populations in island communities for multiple reasons. We examine the influence of three non-structural interventions (reducing departure delays, increasing travel speeds, and managing vegetation to create new paths) that may improve the evacuation potential for at-risk individuals in island communities and use the United States territory of Guam as our case study. We model pedestrian travel times out of a modeled inundation zone for a local tsunami generated by a Mw 8.3 earthquake within the Mariana subduction zone. Evacuation-modeling results indicate that reducing departure delays has a larger impact than increasing travel speeds or creating evacuation corridors through heavy brush on reducing the number of at-risk individuals with insufficient time to evacuate. Travel times to safety are less than wave-arrival times for almost all at-risk individuals in the tsunami-hazard zone if one assumes all three interventions are implemented.

Reducing the vulnerability of tourists to tsunami: challenges for decision-makers

A near source or local tsunami, because of its close proximity to an affected area, cannot usually be predicted soon enough to mitigate many of the risks posed. The limited notice time in local tsunamis poses greater challenges for decision-makers than distant source tsunamis. Tsunamis affect coastal regions, where many of these areas are visited by tourists who often lack adequate knowledge of the hazards of the region. This study focuses on the risks tourists face during a local tsunami and discusses how to best protect tourists. Initially, a thematic literature analysis was performed to identify research gaps. Then, a case study methodology was adopted to obtain an in-depth understanding of how emergency management officials consider the management of tourists in evacuation planning. Napier, New Zealand, was used as a case study because it is a tourist town and vulnerable to tsunamis. Key decision-makers in the disaster management and tourist management sector were interviewed. The results outline three major initiatives that could lead to better tourist management and create better tsunami awareness for tourists. First, the risks posed to tourists can be reduced if emergency management officials collaborate with tourism agencies. Second, developing accurate evacuation simulations can show what would happen to tourists in a tsunami so that emergency management officials can be better prepared, and councils can improve evacuation planning and infrastructure to evacuate tourists and local communities safely. Third, educating tourists about evacuation plans will increase their readiness and enhance their safety.

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.

A Joint Seismic and Space‐Based Investigation of the 2016 Lamplugh Glacier and 2017 Wrangell Mountains (Alaska) Landslides

AbstractLandslides commonly occur in areas with steep topography and abundant precipitation and pose a significant hazard to local communities. Some of the largest known landslides occur in Alaska, including several that caused local tsunamis. Many landslides may have gone undetected in remote areas due to lack of observations. Here, we develop a semiautomated workflow using both seismic and geodetic observations to detect, locate, validate, and characterize landslides in Alaska. Seismic observations have shown promise in continuously monitoring landslide occurrence, while remote sensing techniques are well suited for verification and high‐resolution imaging of landslides. We validate our procedure using the 28 June 2016, Lamplugh Glacier landslide. We also present observations of a previously unknown landslide occurred on 22 September 2017 in the Wrangell Mountains region. The Wrangell Mountains landslide generated a coherent surface wavefield recorded across Alaska and the contiguous United States. We used Sentinel‐1 Synthetic Aperture Radar and Sentinel‐2 optical imagery to map the respective mass deposit. To investigate the landslide dynamics, we inverted regional seismic surface wave data for a centroid single force failure model. Our model suggests that the Wrangell Mountains landslide lasted for about 140 s and had two subevents involving at least five distinct stages. We estimate that the landslide had displaced 3.1–13.4 million tons of rocks over a distance of ∼2 km. Our results suggest that combining seismic and geodetic observations can vastly improve the detection and characterization of landslides in remote areas in Alaska and elsewhere, providing new insights into the landslide dynamics.

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.

Real‐Time Seismogeodetic Earthquake Magnitude Estimates for Local Tsunami Warnings

AbstractWe estimate a seismogeodetic earthquake moment magnitude using unclipped, broadband velocity and displacement waveforms from collocated Global Navigation Satellite Systems and seismic stations located within 800 km epicentral distance for nine 7.2 < < 9.1 earthquakes. We consider the vertical component of seismogeodetic displacement as an approximate source time function and integrate the associated time series to obtain the seismic moment. By continuing to integrate vertical displacement beyond the initial P‐waves, we obtain rapid estimates of that are within 0.2 magnitude units for 8 thrust faulting events and within 0.3 units for the single normal faulting event. Because our estimates of the seismic moment are based on the maximum value of integrated displacement, no regression against other source parameters, or distance, is necessary. Our new method shows promise for integration into earthquake and local tsunami early warning systems, including tsunami earthquakes characterized by relatively slow moment release over a longer rupture time, and earthquakes with complex source time functions.

Tsunami evacuation modelling via micro-simulation model

The associated tsunami risks posed to coastal regions in earthquake-prone areas highlight the importance of an effective emergency evacuation plan for these regions. Evacuation simulations have shown to be a valuable tool in assessing the effectiveness of existing evacuation plans and providing solutions for risk reduction, and improving community readiness. This paper describes the development of a micro-simulation evacuation model (MSEM) to assess the effectiveness of local tsunami evacuation processes and test the results with a velocity-based theoretical model. As an agent-based model, the MSEM considers both pedestrian and vehicle interactions and their interactions with each other. The models were used to assess the evacuation scenarios for a tsunami-prone city Napier, in New Zealand. The evacuation process was evaluated based on a local 8.4 Mw earthquake that would trigger a tsunami event, with an evacuation time of 50 min between feeling the initial shake in Napier City and the time of arrival of the tsunami wave. The study outlined within this paper assumes two scenarios: (1) effected population would evacuate by foot, and (2) affected population would evacuate by car, considered to take place during the afternoon at the traffic peak time. The results of the MSEM show factors such as evacuation method, lane and sidewalk capacities, and interactions between individuals affect the individuals' ability to safely evacuate. The MSEM model based on scenario 1 and 2 for Napier City, demonstrated around 85% of residents would reach designated safe area when all evacuating by foot, whilst, only 45% of evacuees will reach their designated safe zone if all individuals attempted to use vehicles as their means of evacuation.

Investigation of Local Tsunami Effect on Coastal Areas: A Case Study of Putian City, Fujian Province, China

In this paper, we explored the local tsunami hazards induced by an active local seismic Quanzhou fault, along the coastlines of the City of Putian, Fujian Province, in the southeast of China. The simulation results indicated that the tsunami wave will hit the nearest coast of Putian 0.5 h after the earthquake occurs. The most serious tsunami inundation depth in Putian was less than 3.0 m. This study also conducted a sensitivity test of the tsunami amplitude and inundation in response to different seismic source parameters, particularly the rake and strike angles of the Quanzhou fault. Based on the post-earthquake survey and the most updated geophysical data, the uniform dislocation distribution is applied in the range of scientific geometrical characteristic parameters for numerical modeling. A 20° change in the rake angle increases the inundation area from 50.0 km2 to more than 100.0 km2, and increases the tsunami amplitude from 0.2 m to 1.0 m. In this study, the tsunami hazard of Putian is more sensitive to the rake than to the strike angle for a local fault. Tsunamis generated by seismic fault could also result in serious coastal flooding along the coastlines locally, and the time for emergency response is limited. The research results could provide technical support for refining local tsunami hazard assessment and contingency plans, to save decision-making time and avoid waste of social resources.

Local Tsunami Amplification Factors due to the Bathymetric Effect and its Application to Approximate Hazard Assessment on the Zihuatanejo Coast

Local Tsunami Amplification Factors due to the Bathymetric Effect and its Application to Approximate Hazard Assessment on the Zihuatanejo Coast

Stochastic tsunami modeling induced by kinematic complex sources

In this study, local tsunami hazard due to seismic sources is evaluated in a stochastic framework. Several assumptions such as static passive generation, constant rake angle and source centroid (among others) are relaxed. Spatial uncertainties are modeled in a large set of scenarios. The proposed methodology is easy to implement and can be combined with other types of sources or hazards. Application in the Kuril-Kamchatkah trench shows a straightforward use of our methodology, producing simple hazard maps, which can be replicated in any region of the world.