Tsunami Hazard Research Articles

CARIBE WAVE: A Decade of Exercises for Validating Tsunami Preparedness in the Caribbean and Adjacent Regions

ABSTRACT The year 2021 marked a decade of CARIBE WAVE (CW) exercises organized by the United Nations Educational, Scientific and Cultural Organization Intergovernmental Oceanographic Commission Coordination Group for Tsunamis and Other Coastal Hazards Warning System for the Caribbean and Adjacent Regions (ICG CARIBE/EWS). This region has had a long history of devastating tsunamis, and over the years the risk to lives and livelihoods of coastal communities has continued to increase. The tsunami threat in the Caribbean provides a strong incentive for countries to prepare and participate in annual tsunami exercises. The CW exercise is carried out with the purpose of validating and advancing tsunami resilient communities in the region. As a result of these exercises, countries have been able to test and improve communications between the Tsunami Service Provider and their National Tsunami Warning Centers (NTWC) and Tsunami Warning Focal Points (TWFP), as well as practice their emergency response plans. Participation of the public (including mass media communications, social media engagements, tsunami walks, etc.) and regional government beyond TWFP and NTWC has played a critical role in developing tsunami awareness in the greater community. This study collates the history and background of exercises since 2011, resulting in enhancing tsunami preparedness and awareness. Ongoing CW exercises should continue and be strengthened so that the region is prepared as possible to respond and recover when the next tsunami strikes the shores of the Caribbean and Adjacent Regions.

Multi-hazard analysis of flood and tsunamis on the western Mediterranean coast of Turkey

Abstract. Flooding has always been a devastating hazard for social and economic assets and activities. Especially, lowland areas such as coastal regions can be more vulnerable to inundations. The combination of different natural hazards observed at the same time is definitely worsening the situation in the affected regions. The goal of this study is to conduct a distinctive multi-hazard analysis considering flood hazards with the contribution of potential earthquake-triggered tsunamis that might be observed throughout the Fethiye coastline and city center. For this purpose, tsunami hazard curves are generated based on Monte Carlo simulations. Comprehensive stochastic hazard analyses are performed considering the aleatory variability of earthquake-triggered tsunamis and epistemic uncertainty of floods having 10-, 50-, and 100-year return periods. Numerical simulations are conducted to combine the potential tsunamis and flood events that are able to adversely affect the selected region. The results of this study show that the blockage of stream outlets due to tsunami waves drastically increases the inundated areas and worsens the condition for the selected region.

Raised potential earthquake and tsunami hazards at the North Sulawesi subduction zone after a flurry of major seismicity

The North Sulawesi subduction zone (NSSZ) was ruptured by a series of large earthquakes (Mw >7) since 1990s, generally triggered small to moderate tsunamis in the surrounding seas and ocean. But the 2018 Sulawesi Mw 7.5 earthquake ruptured the west subduction zone and induced a large tsunami that displaced hundreds of people. These large earthquakes, especially the deeper thrust events, generated stress loading to the shallow megathrust that could rupture to excite exceptional tsunami hazard as observed in Sumatra, Japan and the other subduction zones. Whether the stress loading from downdip events can trigger future failure of a shallow tsunami earthquake and its ensuring tsunami hazard impact remains elusive. Here we investigate the potential of earthquake and tsunami by analyzing the historical earthquake characteristics, calculating Coulomb stress changes and simulating hundreds of hypothetical earthquake ruptures to assess the plausible tsunami hazard in the NSSZ. Our results show that a series of Mw 7+ downdip megathrust earthquakes have loaded most of the megathrust, especially the shallow portion (<10 km), with increased stress >10 kPa, implicating a high potential of future large earthquakes and ensuring outsize tsunamis. Our modeled tsunami wave heights vary between >0 and 43 m along the North Sulawesi coastlines. One intriguing fact is that the end point of the tsunami wave energy dissipation path gains a comparable tsunami impact as the region in the rupture zone for all the magnitude considered, highlighting a dual-pattern threatened regions in the Celebes Sea. Importantly, the thrust and fold belt structure in the wide outer wedge of the accretionary prism and the strong seafloor bathymetry variation offshore Sulawesi Island could serve an efficient wave-amplification tool that need to be considered in future hazard assessment. Our findings alert that the earthquake and tsunami hazard potential are largely raised by these downdip major earthquakes.

Ensuring a prudent combination of risk insights and a defense-in-depth philosophy through a reinterpretation of hierarchical safety goals

ABSTRACT Recent developments in the nuclear safety framework have highlighted the importance of integrating both probabilistic and deterministic considerations. This study attempts to integrate risk insights from probabilistic risk assessment and defense-in-depth philosophy and enquires into the application of the hierarchical structure of safety goals to the overall safety considerations in the framework of integrated risk-informed decision-making. A thought experiment on tsunami safety in Fukushima helps show that probabilistic considerations can provide useful risk insights for understanding the status of our knowledge regarding tsunami hazards as well as its cliff-edge effects. The object and methodology for compensating for limited knowledge using a defense-in-depth approach is clarified. Accordingly, the author proposes an interpretation of the hierarchical structure of safety goals ensuring a prudent combination of defense-in-depth and risk insights consistent with the strength of knowledge. In this proposition, the safety goals can be regarded not merely as probabilistic risk criteria but also as a tool for balancing the two approaches, better fitting the comprehensive nature of integrated risk-informed decision-making. The findings of this study demonstrate the possibility of logical and coherent consolidation of probabilistic and deterministic considerations under a newly interpreted safety goals hierarchy.

Tsunami Recurrence and Hazard Evaluation for the South Kuril Islands

Tsunami Recurrence and Hazard Evaluation for the South Kuril Islands

Back-projection results for the M w 7.5, 28 September 2018 Palu earthquake-tsunami

A back-projection technique allows seismologists to analyse rupture properties once seismic signals from a dense array of seismic networks are available. The observed waveforms are then traced back in space and time to the source region of an earthquake under investigation. In this study, the method utilised the back-projection image of the recorded high-frequency P-seismic waveforms filtered at 0.25-1.0 Hz by Multiple Signal Classification (MUSIC) processing to estimate the extent and the spread of earthquake rupture propagation of the M w 7.5 Palu event on 28 September 2018, generating a severe tsunami. This study aims to estimate rupture duration, its extent (the distance over which rupture propagates) and the corresponding speed, and rupture directivity (where most of the seismic energy propagates). The results revealed that the front of rupture propagates slightly offset southward at about 2.9 km/s over a distance of ~140 km away from the epicentre for about 49 s before slowing down at much smaller amplitudes after reaching the south end of Palu Bay. This finding is consistent with an NNW-SSE orientation of the active Palu-Koro Fault lying along the bay, suggesting that the strong ground motion is associated with the fault activities. This study has therefore substantial implications for enhanced earthquake and tsunami early warnings, helping the government and local authority build community resilience by warning people at risk from future possible earthquake and tsunami hazards.

Morpho-arrangement study of the anthropogenic landform for potential exposure of tsunami hazard identification in parangtritis, yogyakarta

This research was conducted in the tsunami prone area of Parangtritis, Yogyakarta. The purpose of this study is to classify and analyse the distribution of anthropogenic landforms, as preliminary information to identify the potential exposure to tsunami. The method used in this research is descriptive-comparative, i.e. by comparing the variations of anthropogenic landforms typology within the present management zones (core, restricted, supporting zone). For each zone, the type of human intervention were identified with regard to the following classification: industrogenic, urbanogenic, traffic, agrogenic, water management, tourism, and sports. The anthropogenic landforms are then classified into excavation, planation, and accumulation types. The results of the study were presented in the form of tables and maps of anthropogenic landforms in each management zone. Assessment of the level of exposure to tsunami hazard is carried out qualitatively for each anthropogenic landform in the different management zones. This research revealed that type of intervention in each management zone are varied. The supporting zone and restricted zone have the most complex interventions, i.e. industrogenic, urbanogenic, traffic, water management, tourism, and sports. The excavation, planation, and accumulation forms are very diverse, depend on the people activities in each management zone. A particular human activity in the study area has a certain level of exposure to tsunami hazard. It is necessary to consider for reducing the specific risk to tsunami.

Influence of tidal level on quantifying the probability of nearshore tsunami hazard

Nearshore tsunami hazard can be greatly affected by the tidal level, especially when large tsunami waves meet the high tidal level. This study aims to quantify the probability of the peak nearshore tsunami elevation (PNTE) caused by seismic tsunamis considering the randomness of event occurrence time and the variation of tidal level. The coast around the Pearl River Estuary has been chosen as the study area to show the influence of tidal level on the probability of nearshore tsunami hazard. Two approaches are proposed to calculate the PNTE considering the effect of tide in a probabilistic tsunami assessment framework. One approach is a linear superposition of tsunami wave upon the tidal level, and the other considering the influence of tidal level on tsunami nearshore amplification. The probability of the PNTE along the concern coast is obtained. The results considering the effect of tide show that the PNTE corresponding to short return period is obviously larger than that based on the mean sea level, but no obvious difference in the case of long return period. Moreover, in the study area, the two approaches considering the effect of tide show only slight difference in estimating the probability of PNTE, which suggests the applicability of the linear superposition method in nearshore tsunami hazard assessments.

Non‐Stationary Probabilistic Tsunami Hazard Assessments Compounding Tides and Sea Level Rise

AbstractTides are often the largest source of sea levels fluctuations. Two new probabilistic tsunami hazard assessments (PTHA) methods are proposed to combine the tidal phase uncertainty at the moment of tsunami occurrence with other sources of uncertainty. The first method adopts a Stochastic Reduced Order Model (SROM) producing sets of tidal phase samples to be used in tsunami simulations. The second method uses tsunami simulations with prescribed collocation tidal phases and tide probability distributions to model the uncertainty. The methods are extended to non‐stationary probabilistic tsunami hazard assessment, compounding tsunamis, tides and sea level rise (SLR). As an illustration, these methods are applied for assessing tsunamis generated in the Manila Subduction Zone, on the coasts of Kao Hsiung and Hong Kong. While the SROM‐based method is faster solving for the PTHA if only tides are considered, the collocation‐based method is faster when both SLR and tides are considered. For the illustration case, tides have a relevant impact on PTHA results, however, the SLR within an exposure time of 100 years has stronger impact. PTHA curves of the maximum tsunami elevation are affected by tides and SLR differently. While tides and SLR increase the dispersion of PTHA hazard curve distributions, the latter also produces a translation toward higher elevations. The development of formulations based on SROM or collocation tides is the key to establishing a method which feasibly can be applied to other regions for comprehensive analysis at a global scale.

Multi-hazard assessment in Palu Barat District

West Palu District is one of the areas severely affected by the earthquake that occurred on September 28, 2018. The purpose of this study was to assess the level of multi-hazard disasters in the West Palu District. The study was conducted by assessing each disaster hazard, namely the hazard of earthquakes, tsunamis, and liquefaction presented in a multi-hazard map. The earthquake hazard assessment parameter is based on PGA data. The tsunami hazard parameter is based on data from the highest peak of a tsunami wave that has ever occurred. Meanwhile, the liquefaction hazard parameter is based on the ground shear strain (GSS) value. Then the weighting and overlapping methods are carried out to obtain the final result in a multi-hazard assessment map. The results showed that the level of multi-hazard in West Palu District was in the medium and high class. The middle multi-hazard level is in Baru Village, Kamonji Village, and Siranindi Village. In contrast, the high multi-hazard level is in Balaroa Village, Ujuna Village, and Lere Village.

Probabilistic tsunami hazard assessment based on the Gutenberg–Richter law in eastern Shikoku, Nankai subduction zone, Japan

Earthquake and tsunami predictions comprise huge uncertainties, thus necessitating probabilistic assessments for the design of defense facilities and urban planning. In recent years, computer development has advanced probabilistic tsunami hazard assessments (PTHAs), where hazard curves show the exceedance probability of the maximum tsunami height. However, owing to the lack of historical and geological tsunami records, this method is generally insufficient for validating the estimated hazard curves. The eastern coast of Shikoku in the Nankai subduction zone, Japan, is suitable for validation because tsunami records from historical Nankai Trough earthquakes are available. This study evaluated PTHAs by comparing the tsunami hazard curves and exceedance frequencies of historical Nankai Trough tsunamis. We considered 3480 earthquake scenarios representing the rupture patterns of past Nankai earthquakes and calculated all tsunamis. The probability of earthquake occurrence was based on the Gutenberg–Richter law. We considered uncertainty in tsunami calculations with astronomical tide variations. The estimated tsunami hazard curves are consistent with the exceedance frequencies obtained from historical tsunamis. In addition, sensitivity tests indicate the significance of the earthquake slip heterogeneity and tsunami defense facilities in PTHAs. We also extended the PTHAs to tsunami inundation maps in high resolution and proposed an effective new method for reducing the tsunami computation load.Graphical

Dynamic Modeling of Interactions between Shallow Slow-Slip Events and Subduction Earthquakes

Abstract Shallow slow-slip events (SSEs) contribute to strain release near the shallow portions of subduction interfaces and may contribute to promoting shallow subduction earthquakes. Recent efforts in offshore monitoring of shallow SSEs have provided evidence of possible interactions between shallow SSEs and megathrust earthquakes. In this study, we use a dynamic earthquake simulator that captures both quasi-static (for SSEs) and dynamic (for megathrust earthquakes) slip to explore their interactions and implications for seismic and tsunami hazards. We model slip behaviors of a shallow-dipping subduction interface on which two locally locked patches (asperities) with different strengths are embedded within a conditionally stable zone. We find that both SSEs and earthquakes can occur, and they interact over multiple earthquake cycles in the model. Dynamic ruptures can nucleate on the asperities and propagate into the surrounding conditionally stable zone at slow speeds, generating tsunami earthquakes. A clear correlation emerges between the size of an earthquake and SSE activities preceding it. Small earthquakes rupture only the low-strength asperity, whereas large earthquakes rupture both. Before a large earthquake, periodic SSEs occur around the high-strength asperity, gradually loading stress into its interior. The critically stressed high-strength asperity can be ruptured together with the low-strength one in the large earthquake, followed by a relatively quiet interseismic period with very few SSEs and then a small earthquake. An SSE may or may not directly lead to nucleation of an earthquake, depending on whether a nearby asperity is ready for spontaneously dynamic failure. In addition, because of different SSE activities, the coupling degree may change dramatically between different interseismic periods, suggesting that its estimate based on a short period of observation may be biased.

Coseismic Faulting Complexity of the 2019 Mw 5.7 Silivri Earthquake in the Central Marmara Seismic Gap, Offshore Istanbul

Abstract The submarine Main Marmara fault is overdue for an M &amp;gt; 7 earthquake in direct vicinity to the Istanbul megacity and the only segment of the right-lateral North Anatolian fault zone that has not been activated since 1766. On 26 September 2019, an Mw 5.7 earthquake occurred offshore Silivri (west of Istanbul), stimulating the discussions on a future major earthquake. The predominant faulting style for this pending earthquake remains enigmatic. Here, we study the coseismic rupture evolution of the 2019 Silivri earthquake and decipher the multitype-faulting aspects by a nonstandard approach. The event was dominated by a large compensated linear vector dipole component, of about −50%, that we interpret as a consecutive strike-slip and thrust double-couple episode, closely collocated in space and time. Because of local variations of the fault geometry at the eastern boundary of the central basin, crustal shortening and related thrust faulting are expected. A striking observation is the almost synchronous occurrence of both faulting types during a single earthquake. The earthquake complexity here is reported for the first time in the Sea of Marmara region and has to be considered in future rupture scenarios of an expected M &amp;gt; 7 event, with subsequent consequences for tsunami hazard and risk.

Fundamentals of Fast Tsunami Wave Parameter Determination Technology for Hazard Mitigation.

This paper describes two basic elements of the smart technology, allowing us to bring to a new level the problem of early warning and mitigation of tsunami hazards for the so-called near zone events (when a destructive tsunami wave reaches the nearest coast in tens of minutes after the earthquake). The sensors system, installed in a reasonable way (to detect a wave as early as possible), is capable of transmitting the necessary raw data (measured wave profile) in a real time mode to a processing center. The smart (based on mathematical theory) algorithm can reconstruct an actual source shape within a few seconds using just a part of the measured wave record. Using modern computer architectures (Graphic Processing Units or Field Programmable Gates Array) allows computing tsunami wave propagation from the source to shoreline in 1–2 min, which is comparable to the performance of a supercomputer. As is observed, the inundation zone could be evaluated reasonably correctly as the coastal area below two thirds of the tsunami wave height at a particular location. In total, the achieved performance of the two above mentioned algorithms makes it possible to evaluate timely the tsunami wave heights along the coastline to approximate the expected inundation zone, and therefore, to suggest (in case of necessity) evacuation measures to save lives.

Spatial Distribution of Tsunami Hazard Posed by Earthquakes along the Manila Trench

Quantitative probability has been computed for the tsunami hazard posed by earthquakes from the Manila Trench, which has been regarded as a huge threat in the South China Sea. This study provides a spatial distribution of the tsunami hazard covering the affected area with a spatial resolution of 0.1° for disaster prevention of islands and continental coasts. The quantitative probability of the tsunami hazard is computed by an efficient model, which can realize a large amount of potential tsunami scenarios analysis in order to consider the randomness and uncertainty in earthquake magnitude, source location and focal depth. In the model, for each potential tsunami scenario, the occurrence probability of the corresponding earthquake and the intensity of tsunami waves at each target location are computed. The occurrence probability of each scenario is estimated based on the historical earthquake records. Then, the subsequent tsunami caused by each scenario is computed using a new, efficient approach, instead of direct simulation using an ocean dynamics model. A total of 1,380,000 scenarios are computed in order to obtain a stable statistical result. Based on the results, the spatial distribution of the tsunami hazard is discussed and high-hazard regions along the coast have been identified.

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.

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.

Stochastic source modeling and tsunami simulations of cascadia subduction earthquakes for Canadian Pacific coast

ABSTRACT This study presents new stochastic source models for the Cascadia subduction earthquakes in the Pacific Northwest, which can trigger massive tsunamis along the shoreline of Vancouver Island. An extensive set of 5,000 stochastic source models is generated for the moment magnitude ranges between 8.1 and 9.1, and regional tsunami hazard simulations are performed at the grid resolution of 270 m. The results from the stochastic tsunami simulations are characterized by evaluating the regional tsunami hazard metric that is based on the geometric mean of the maximum wave heights along the Vancouver Island coast. Subsequently, using the probability distribution of the regional tsunami hazard parameter, representative source models are identified by capturing the average as well as rare rupture cases and then detailed tsunami hazard results, such as maximum wave height maps and wave profiles at specific locations, are examined. Numerical results highlight the directivity effects of tsunami generation and wave propagation on tsunami hazards along the Canadian Pacific coast and the earthquake source characterizations in terms of fault geometry and earthquake slip distribution. The developed source models and tsunami simulation results serve as the first step for performing probabilistic tsunami hazard analysis for the Cascadia subduction zone.

Application of external flood probabilistic safety assessment methodology to Prototype Fast Breeder Reactor

ABSTRACT This paper presents the methodology adopted, accident sequence analysis and salient results from the external flood probabilistic safety analysis exercise for Prototype Fast Breeder Reactor. The major steps performed are the probabilistic hazard estimation, fragility computation, system reliability modelling and risk quantification. The hazard analysis has been performed for rainfall, storm surge and tsunami as typically associated with a coastal site, from which correlation function relating flood level to the annual exceedance frequency is estimated. The fragility analysis of different safety systems is estimated by considering submergence mode of failure using step fragility functions. The secondary effects of flood such as debris impact, load falling and flood-induced sodium fires are not considered. The human reliability analysis of manual operations necessary for plant safety is done for the control room as well as onsite actions. The challenges encountered during the analysis, salient results and uncertainties involved are presented with inferences. Abbreviations: AHX: air heat exchanger; CDF: core damage frequency; EFPSA: external flood probabilistic safety assessment; EL: elevation levels; EOP: emergency operation procedure; ET: event tree; FT: fault tree; HRA: human reliability analysis; IE: initiating events; NPP: nuclear power plant; OGDHRS: operation grade decay heat removal system; PFBR: prototype fast breeder reactor; POT: peak over threshold; PSA: probabilistic safety assessment; PTHA: probabilistic tsunami hazard assessment; RY: reactor year; RCB: reactor containment building; RP: return period; SGDHRS: safety grade decay heat removal system; SSC: structures, systems and components

Development of the Japan Tsunami Hazard Information Station (J-THIS)

To promote effective disaster countermeasures against possible tsunamis in the future, an effective application of tsunami hazard information is important. However, there were insufficient systems available for utilizing and applying various tsunami hazard information. Based on this situation, we developed and have been improving the Japan Tsunami Hazard Information Station (J-THIS), an open Web system available as a public portal for providing tsunami hazard information based on the probabilistic tsunami hazard assessment (PTHA). It provides tsunami hazard information through the following services: map services, data download services, and Web application programming interface (API) services. Based on the PTHA along the Nankai Trough, the J-THIS provides distributions of exceedance probability of tsunami heights for 30 years, tsunami hazard curves, earthquake fault models, tsunami heights for each earthquake fault model, and bathymetric charts. To illustrate the use of the J-THIS, understanding how existing coastal structures will protect us against tsunamis while enabling the local governments to set investment priorities in disaster risk reduction and resilience is key.