Search

New Makran simulations imply two generalized zones of mid-field tsunami hazard in greater Karachi. The simulations presuppose seven megathrust ruptures that strike east-west, range in area from 100 × 150 km to 355 × 800 km, and lie west of the city by no less than 100 km. The assumed seismic slip is uniform across each rupture area. The smallest rupture approximates the 1945 Makran earthquake of magnitude 8.1, while the largest corresponds to a previously conjectured giant Makran earthquake of magnitude 9.2. None of the sources include a complication in 1945: late-arriving waves from submarine slides or splay faulting. Consequently, the first simulated wave is the largest in each of the seven scenarios. And because the sources are to the west, the simulated waves are higher, and arrive sooner, at Karachi Port (1.5 hr) than 30 km farther east at Port Qasim (nearly 3 hr). These combinations of height and arrival time can be generalized as properties of two hazard zones: a western one that includes Karachi Port, and an eastern one that includes Port Qasim. The simulated flooding extends farthest inland into low-lying residential areas of the western zone. Neither hazard zone is near-field or far-field. That is, neither is near enough to the fault ruptures for felt seismic shaking to dependably warn of a fast-arriving tsunami, yet neither is distant enough to receive more than three hours of advance notice through tsunami warning systems. Our simulations are intended to support emergency management in this mid-field setting. [ABSTRACT FROM AUTHOR]

Estimating coastal tsunami impact for early-warning or long-term hazard analysis requires the calculation of inundation metrics such as flow-depth or momentum flux. Both applications require the simulation of large numbers of scenarios to capture both the aleatory variability and the epistemic tsunami uncertainty. A computationally demanding step in simulating inundation is solving the non-linear shallow water (NLSW) equations on meshes with sufficiently high resolution to represent the local elevation accurately enough to capture the physics governing the flow. This computational expense is particularly challenging in the context of Tsunami Early Warning where strict time constraints apply. A machine learning (ML) model that predicts inundation maps from offshore simulation results with acceptable accuracy, trained on an acceptably small training set of full simulations, could replace the computationally expensive NLSW part of the simulations for vast numbers of scenarios and predict inundation rapidly and with reduced computational demands. We consider the application of an encoder–decoder based neural network to predict high-resolution inundation maps based only on more cheaply calculated simulated time-series at a limited number of offshore locations. The network needs to be trained using input offshore time-series and the corresponding inundation maps from previously calculated full simulations. We develop and evaluate the ML model on a comprehensive set of inundation simulations for the coast of eastern Sicily for tens of thousands of subduction earthquake sources in the Mediterranean Sea. We find good performance for this case study even using relatively small training sets (order of hundreds) provided that appropriate choices are made in the specification of model parameters, the specification of the loss function and the selection of training events. The uncertainty in the prediction for any given location decreases with the number of training events that inundate that location, with a good range of flow depths needed for accurate predictions. This means that care is needed to ensure that rarer high-inundation scenarios are well-represented in the training sets. The importance of applying regularization techniques increases as the size of the training sets decreases. The computational gain of the proposed methodology depends on the number of complete simulations needed to train the neural network, ranging between 164 and 4196 scenarios in this study. The cost of training the network is small in comparison with the cost of the numerical simulations and, for an ensemble of around 28 000 scenarios, this represents a 6- to 170-fold reduction in computing costs. [ABSTRACT FROM AUTHOR]

This study provides a dataset and shows the spatial distribution of tsunami hazard in the South China Sea sourced from the Manila subduction zone. The plate motion data around the Manila subduction zone are used to invert the geodetic locking of the Manila subduction zone, further used to estimate the maximum possible magnitude and applied to obtain a more reliable tsunami hazard assessment. The spatial distribution of tsunami wave height with a 1000-year return period is shown, and several high-hazard areas in the South China Sea are pointed out. Uncertainties in the seismic source are explored, including the slip heterogeneity, the upper limit of seismic magnitude and segmentation. The impact of the locking distribution and randomness of slip on tsunami hazard assessment demonstrates that the traditional uniform slip assumption significantly underestimates the tsunami hazard. Moreover, the assessment results involving the effect of the locking distribution should be more realistic and show a larger tsunami height than when only considering the stochastic slip in most areas, which should prompt coastal management agencies to enhance tsunami prevention awareness. [ABSTRACT FROM AUTHOR]

Earthquakes in coastal areas frequently trigger tsunami waves, posing significant threats to low-lying coastal bridges. Investigating extreme wave force on bridge deck is crucial for understanding bridge damage mechanisms. However, the majority of current research focuses on single bridge deck, with limited analysis of wave impacts on twin bridge decks. In this paper, solitary wave is utilized to simulate tsunami wave, and a two-dimensional (2D) computational fluid dynamics (CFDs) model to analyze wave–bridge interactions and investigate the impact of tsunami wave on adjacent twin box-girder bridge decks. The numerical model was validated by solitary wave theory and wave force data obtained from the published experiment. Based on this model, the effects of the submergence coefficient, wave height, and deck spacing on the horizontal and vertical forces on the twin box-girder bridge decks were analyzed and compared with those in a single box-girder bridge deck. The results indicate that, firstly, due to wave reflection and the trapped water, the vertical wave force on the twin forward bridge deck significantly surpasses that on the single bridge deck. Furthermore, the twin backward bridge deck experiences greater horizontal force than single deck when the deck is completely submerged. Secondly, the maximum wave force on the twin bridge decks does not always consistently decrease with increasing deck spacing. Finally, the negative horizontal force would exceed the positive horizontal force on the twin forward bridge deck under higher wave. This paper delineates the disparities between twin and single box-girder bridge deck responses to wave action and analyzes the influencing factors. Such insights are pivotal for coastal bridge construction and natural disaster risk assessment. [ABSTRACT FROM AUTHOR]

The Makran Subduction Zone (MSZ) in the northwestern Indian Ocean can generate large tsunamigenic thrust earthquakes affecting the coastal regions of Pakistan, Iran, Oman, and western India. In this paper, a probabilistic tsunami hazard assessment is conducted for the MSZ using stochastic tsunami simulations of moment magnitude (Mw) of 7.7–9.1 earthquake scenarios. This study investigates uncertainties associated with earthquake occurrence rate, single-segment (eastern and western MSZ) or two-segment (full MSZ) rupture scenarios, source geometry, and slip heterogeneity. The total number of simulated source models is 15,000. This study presents two major categories of results: stochastic source models and ranges of 475, 975, and 2475-year tsunami heights. For instance, tsunami heights generated by Mw 8.5‒8.7 stochastic sources of western MSZ vary between 1 m and 10 m with a mean of ~ 4.5 m in the affected areas. The tsunami heights are sensitive to the source models' characteristics, such as location of the large slip areas, bathymetry of the nearshore area, and the location of bays. Considering different occurrence rates results in significant variability in the estimated 475, 975, and 2475-year tsunami heights. For example, 2475-year tsunami height in Chabahar is in the range of 3‒7.4 m at 10 m water depth. [ABSTRACT FROM AUTHOR]

The initial condition for the simulation of a seismically-induced tsunami for a rapid, assumed instantaneous, vertical seafloor displacement is given by the Kajiura low-pass filter integral. This work proposes a new efficient and accurate approach for its numerical evaluation, valid when the sea floor displacement is discretized as a set of rectangular contributions. We compare several truncated quadrature formulae, selecting the optimal one. We verify that we can satisfactorily approximate the initial sea level perturbation as a linear combination of those induced by the elementary sea floor displacements. The methodology is tested on the tsunamigenic Kuril earthquake doublet – a megathrust and an outer-rise – occurred in the Central Kuril Islands in late 2006 and early 2007. We also confirm the importance of the horizontal contribution to the tsunami generation and we consider a simple model of the inelastic deformation of the wedge, on a realistic bathymetry. The proposed approach results accurate and fast enough to be considered relevant for practical applications, and a tool is provided to create tsunami unit source databases for a given region of interest. [ABSTRACT FROM AUTHOR]

This study aims to build a computer model to detect built-up land in the identified tsunami hazard zone based on Sentinel 2A imagery using the normalized built up area index (NBI), urban index (UI), normalize difference build-up index (NDBI), a modified built-up index (MBI), index-based builtup index (IBI) algorithms, optimized with machine learning Random Forest (RF) and extreme gradient boosting (XGboost) algorithms and the spatial patterns are predicted using the ordinary kriging (OK) method. Testing of the accuracy of the classification and optimization results was performed using the Kohen Kappa and overall accuracy functions. The results of the study show that a built-up land consisting of open land and water, settlements, industry areas, and agriculture and tourism areas can be identified using the parameters of built-up indices. The accuracy testings that were performed using overall accuracy and Kohen Kappa methods show that classification and prediction are highly accurate using XGboost machine learning, namely >91%. This study produces a novelty of finding, namely a computer model to detect and predict the spatial distribution of built-up land in 4 scales, i.e., very low, low, high, and very high based on NBI, UI, NDBI, MBI, IBI data extracted from Sentinel 2A imagery. [ABSTRACT FROM AUTHOR]

Background: The Mediterranean Sea is a region characterized by high seismic activity, with at least 200 tsunami events recorded from the fourth century to the present twenty-first century. Numerous studies have been conducted to understand past tsunami events, earthquake–tsunami generation, tsunami recurrence periods, tsunami vulnerability zones, and tsunami hazard mitigation strategies. Therefore, gaining insights into future trends and opportunities in Mediterranean Sea tsunami research is crucial for significantly contributing to all relevant aspects. This study aims to assess such trends and opportunities through a scientometric analysis of publications indexed by Web of Science from 2000 to 2023. Results: Based on a selection of 329 publications, including research articles, review articles, book chapters, and conference papers, published between 2000 and 2023, Italy has the highest number of publications and citations in this field. The number of publications has increased significantly, especially after the 2004 Indian Ocean, 2011 Tohoku, and 2018 Palu tsunamis. According to the keyword analysis, the terms "tsunami", "earthquake", "hazard", "wave", "Mediterranean", "coast", and "tectonic" were the most frequently used in these publications. Research themes consist of four classifications: motor themes, such as seismic hazard; specific but well-developed themes, like tsunamiite; emerging or disappearing themes, for example, climate change; and general or basic themes, such as equations and megaturbidite. The number of publications related to the motor theme classification continued to grow throughout 2000–2023. Topics from 2011–2023 are more complex compared to 2000–2010, characterized by the emergence of new keywords such as evacuation planning, risk reduction, risk mitigation, building vulnerability, coastal vulnerability, climate change, probabilistic tsunami hazard assessment (PTVA-3 and PTVA-4). However, topics that were popular in the 2000–2010 period (e.g., paleotsunami deposits, earthquake, and tsunami propagation analysis) also increased in 2011–2023. Conclusions: Research topics with high centrality and density such as seismic hazard will continue to develop and prospect. The cluster network of this topic includes seismoturbidites, sedimentary features, tsunami modeling, active faults, catalog, and historical earthquakes. [ABSTRACT FROM AUTHOR]

Along the French Mediterranean coastlines, most of the studies dealing with tsunamis have focused on hazards, evacuations, or effects of awareness actions, as opposed to hazard perception and knowledge of alert declared locally by the population. To bridge this gap, in this study, data collection yielded 750 responses coming from 150 people living and/or working in the tsunami evacuation zones of five municipalities (e.g., Bandol, Bastia, Cannes, Six-Fours-les-Plages, Sanary-sur-Mer). Early findings confirmed the tendency to underestimate tsunami hazard and a misunderstanding of the alert process. Interestingly, age or location of respondents explained differences between the five surveyed municipalities – more so than gender and residency status. Discrepancies are also observed when we compare the rate of correct answers for similar questions addressed in other areas in the NEAMTWS (North-eastern Atlantic, Mediterranean and connected seas Tsunami Warning System) region, thus confirming local effects. More surprisingly, the respondents who well perceive the tsunami hazard are not those who have a good knowledge of alerts, and the awareness actions do not really impact the tsunami knowledge we evaluated. Also, the results of this study could help local authorities to develop future tsunami awareness actions and to determine more suitable strategies to be applied in the short term at local scales. [ABSTRACT FROM AUTHOR]

This research was conducted to analyze land use change from 2016 to 2022 and their impact on the tsunami hazard zone on the coast of Kebumen Regency. For land use change analysis, remote sensing, geographic information systems (GIS), and statistical tests were applied to Sentinel-2A satellite imagery. The tsunami hazard was simulated using tsunami inundation modeling based on land use spatial data and DEMNAS processed using GIS. Land use changes occurred significantly in the study area, especially in Mirit District. The Southern Cross Road (JJLS) and coastal morphological conditions influence land use change patterns. Land use changes impact changes in the tsunami hazard zone, especially in the use of fir forests and shrimp ponds. The research findings can be used as input for developing a tsunami disaster mitigation plan and detailed spatial planning on the coast of Kebumen Regency. [ABSTRACT FROM AUTHOR]

This study describes a novel method of assessing risk communication effectiveness by reporting an evaluation of a tsunami information brochure by 90 residents of three Pacific coast communities that are vulnerable to a Cascadia Subduction Zone earthquake and tsunami—Commencement Bay, Washington; Lincoln City, Oregon; and Eureka, California. Study participants viewed information that was presented in DynaSearch, an internet‐based computer system that allowed them to view text boxes and tsunami inundation zone maps. DynaSearch recorded the number of times each text box or map was clicked and the length of time that it was viewed. This information viewing phase was followed by questionnaire pages assessing important aspects of tsunami hazard and sources of tsunami warnings. Participants gave the longest click durations to what to do in the emergency period during earthquake shaking and in its immediate aftermath before a tsunami arrives—topics that should be displayed prominently in tsunami brochures and emphasized in talks to community groups. The smallest adjusted click durations were associated with advance preparations for a tsunami—topics that can be posted on websites whose URLs are printed in the brochures. [ABSTRACT FROM AUTHOR]

Some areas of the California coast have physical conditions—such as local bathymetry, topography, shoreline orientation, and other factors—that increase the risk for damage from tsunami inundation compared with other regions. Technical tsunami hazard analyses can inform decision-makers on regional planning and policy decisions. In this paper, we focus on recent efforts in California to delineate various tsunami hazard zones along the coastline under the Seismic Hazard Mapping Act, wherein structural mitigation measures will be recommended. To define the zone wherein structural mitigation measures are recommended, we present a state-wide tsunami reliability analysis that combines existing probabilistic hazard information and structure fragility curves derived from recent events. We examine design-life chances of significant structural damage for various structure types along all developed coastlines throughout California and use this analysis to show how hazard and risk have different correlations throughout the State. Finally, we outline an approach for creating mitigation zones, which provides state-wide tsunami risk consistency for all structures in the tsunami inundation zone. [ABSTRACT FROM AUTHOR]

Greece is located in one of the most seismically active regions in Europe. Many seismic hazard studies have been performed for various sites around Greece, at a regional or local scale. However, the latest national seismic hazard map, currently used for the seismic design of buildings and infrastructure, was published in 2000 and has not been updated since then. In light of recent advances in seismic source and ground motion modeling, the present study focuses on a comparative Probabilistic Seismic Hazard Assessment (PSHA) for the region of East Macedonia and Thrace (EMTH), located in Northern Greece. Various seismic source models are implemented and compared against an updated earthquake catalog to form the necessary source model logic tree. The ground motion logic tree is composed of Ground Motion Prediction Equations (GMPEs), which have been proven suitable for implementation in Greece. PSHA results are presented for the most important cities of East Macedonia and Thrace in a comparative way, which highlights the variability of the seismic hazard among the various seismic source models. An updated seismic hazard map of the study area is proposed, and a comparative disaggregation analysis is performed to estimate the earthquake scenarios with the largest contribution to the seismic hazard. [ABSTRACT FROM AUTHOR]

On 6 February 2023, an M7.8 devastating earthquake started rupturing the East Anatolian fault system in Turkey, resulting in intense shaking that lasted over a minute. A second earthquake of magnitude 7.5 struck near the city of Elbistan a few hours later. Both of these events are associated with the East Anatolian fault system. The earthquake sequence caused widespread damage and collapse of structures in densely populated areas throughout the Southern Turkey and Northern Syria regions and a very large number of human losses. This study focuses on the correlation of the ground deformation with the critical exposure of the infrastructures of Gaziantep and Kahramanmaraş cities. The estimation of the ground deformation of the affected area is achieved with the use of Copernicus Sentinel-2 products and the Normalized Cross Correlation algorithm (NCC) of image matching. The results of the East–West component show that specific sections of the region moved towards the East direction, reaching displacement measurements of 5.4 m, while other sections moved towards the West direction, reaching displacement measurements of 2.8 m. The results of the North–South component show that almost the whole affected area moved towards the North direction, with specific areas reaching displacements of 5.5 m, and a few exemptions, as some areas moved towards the South direction, with displacements reaching even 6.9 m. Regarding the cities of Kahramanmaraş and Gaziantep, their estimated movement direction is North-West and North-East, respectively, and is consistent with the movements of the Arabian and Anatolian Plates in which they are located. Important infrastructures of the study areas (education, museums, libraries, hospitals, monuments, airports, roads and railways) are superimposed on the findings, enabling us to detect the critical exposure rapidly. [ABSTRACT FROM AUTHOR]

Tsunami hazard analysis is an essential step for designing buildings and infrastructure and for safeguarding people and assets in coastal areas. Coastal communities on Vancouver Island are under threat from the Cascadia megathrust earthquakes and tsunamis. Due to the deterministic nature of current megathrust earthquake scenarios, probabilistic tsunami hazard analysis has not been conducted for the coast of Vancouver Island. To address this research gap, this study presents a new probabilistic tsunami hazard model for Vancouver Island from the Cascadia megathrust subduction events. To account for uncertainties of the possible rupture scenarios more comprehensively, time-dependent earthquake occurrence modeling and stochastic rupture modeling are integrated. The time-dependent earthquake model can capture a multi-modal distribution of inter-arrival time data on the Cascadia megathrust events. On the other hand, the stochastic rupture model can consider variable fault geometry, position, and earthquake slip distribution within the subduction zone. The results indicate that the consideration of different inter-arrival time distributions can result in noticeable differences in terms of site-specific tsunami hazard curves and uniform tsunami hazard curves at different return period levels. At present, the use of the one-component renewal model tends to overestimate the tsunami hazard values compared to the three-component Gaussian mixture model. With the increase in the elapsed time since the last event and the duration of tsunami hazard assessment, the differences tend to be smaller. Inspecting the regional variability of the tsunami hazards, specific segments of the Vancouver Island coast are likely to experience higher tsunami hazards due to the directed tsunami waves from the main subduction zone and due to the local underwater topography. [ABSTRACT FROM AUTHOR]

A total of ten tsunami events occurred in Aceh Province from 1991 to 2012. This condition confirms that Aceh Province is very vulnerable to tsunami hazards. In 2004, a tsunami occurred due to the activity of the subduction zone on the west coast of Aceh with a magnitude of Mw 9.3. Since the 2004 tsunami, research on tsunamis has increased. The aim of this study is to reconstruct the 2004 tsunami models, to find out which models are suitable for the events of 2004. There are at least five models of earthquake source faults used for tsunami modeling in this study. The tsunami modeling was carried out numerically using the Tohoku University's Numerical Analysis Model Investigation (TUNAMI) programme. The maximum height obtained from the modeling is 58,05 m at the shoreline. The maximum height obtained from the best model is 17,73 m on land. The M5 fault model produced a tsunami height model that best matches the observation results validated by lowest RMS and highest correlation coefficient values. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

On 14 November 2016, the Mw 7.8 Kaikōura earthquake and tsunami occurred in Aotearoa New Zealand, impacting the city of Te Whanganui-a-Tara (Wellington). As many people reside in apartments in Wellington, we undertook a survey followed by interviews to understand evacuation information communicated to apartment dwellers, and how residents used that information for decision-making. Immediately following earthquake shaking, some apartment dwellers stayed in their building as per official advice, while others evacuated because they felt safer outside. A small proportion evacuated because of the tsunami threat, and many of these participants did so because of the 'Long or Strong, Get Gone' evacuation advice. Others were unclear whether their apartment building was in a tsunami evacuation zone. Some returned immediately after the initial evacuation, while others with damaged apartments evacuated for weeks to months. Participants used regular information upates particularly via social media channels, to inform decisions about returning after longer-term evacuation. However, communicating with the Body Corporate or landlord was difficult, and apartment dwellers reported having trouble getting information about the damage status of their building, making decisions about returning challenging. Given the unique context of apartment dwellers, communication strategies should be honed to assist responses to a future event. [ABSTRACT FROM AUTHOR]

Tsunami risk is considered as the probability of a particular coastline being struck by a tsunami that may cause a certain level of impact (destructiveness). The impact metric of a tsunami is expressed in terms of tsunami intensity values, K, assigned on a 12-degree scale. To calculate tsunami risk we are based on the tsunami history of the region codified in tsunami catalogues. The probabilistic model adopted was used successfully for hazard assessment of earthquakes (Kijko et al. in Bull Seismol Soc Am 79:645–654, 2016) and of tsunamis (Smit et al. in Environmetrics 30:e2566, 2019) by considering seismic magnitude and tsunami height as metrics of the respective hazards. In this model, instead of hazard metrics we inserted risk metric, i.e. wave impact in terms of intensity values. The procedure allows utilization of the entire data set consisting not only from the complete (recent) part of tsunami catalogue but also from the highly incomplete and uncertain historical part of the catalogue. Risk is assessed in terms of probabilities of exceedance and return periods of certain intensity values in specific time frames. We applied the model using catalogues for the Mediterranean and connected seas. Sensitivity analysis showed that using complete data sets generally provided more realistic results than using entire data sets. Results indicated that the risk level depends on the seismicity level and not on the size of individual ocean basin. The highest tsunami risk level was found in the eastern Mediterranean (EM), with a significantly lower risk in the western Mediterranean (WM). In the Marmara Sea (MS), the tsunami risk was low, and the lowest was in the Black Sea (BS). The risk in the small Corinth Gulf (CG, Central Greece) was comparable to that of WM. The return period of damaging tsunamis (i.e. K ≥ 7) was 22 years in the entire Mediterranean basin and 31, 118, 135, 424, and 1660 years in the EM, WM, CG, MS, and BS basins, respectively. [ABSTRACT FROM AUTHOR]

Inspired by the goal of Kuroshio Town, a coastal community in southern Japan, to have zero casualties from the next tsunami, this study will focus on a tsunami preparedness program to save everyone's life. The first step in the program is to determine how many people in a tsunami hazard zone can be protected using existing horizontal and vertical evacuation procedures and shelters. The people who live or work in tsunami hazard zones but cannot or will not use these shelters are identified as "unprotected". A possible solution to save the "unprotected" is to offer a shelter-in-place option to complement the horizontal and vertical evacuation options. Such a shelter-in-place option would provide protection for those unable or unwilling to use horizontal or vertical evacuation facilities. The shelter-in-place option would offer customized protection for individuals and businesses free of contagious diseases found in gatherings associated with horizontal or vertical evacuation shelters. To be effective, the shelter-in-place option must be immediately accessible to protect people from drowning, being crushed, being hit by floating objects, suffocation by ingesting silt laden water, fires, and hypothermia. An example of a shelter-in-place product is a patented, spherical aluminum capsule that floats on the tsunami protecting people from fire, cold water, being crushed, ingesting contaminated water, being hit by floating objects, and drowning. Since the capsule floats, there is no need to accurately predict tsunami flooding heights. This study includes numerical model simulations for 20 capsules subjected to 3 tsunami flooding scenarios in Newport, Oregon indicating the capsules have a low probability of being washed out to sea. Using a shelter-in-place option, along with horizontal and vertical evacuation options, zero casualties from the next tsunami is possible. [ABSTRACT FROM AUTHOR]

Since the major tsunami that occurred in 2004, many studies have dealt with the evacuations, hazard mapping and awareness-actions, rather than on the perceived tsunami risk nor on alert perceptions declared locally by the population. In this study, we analyzed a sample of 750 answers to a face-to-face questionnaire, gathered from residents or workers in 5 densely-urbanized municipalities (e.g., Bandol, Bastia, Cannes, Six-Fours-Les-Plages, Sanary-sur-Mer), likely to be hit by a tsunami and bordering the French Mediterranean basin. Results first confirmed the tendency to underestimate the tsunami risk, as only 15.6 % identify tsunami as a risk. However, 48.7 % declare they should take protective actions if they feel ground-shaking on the seafront, and even 65.3 % if they also see a anormal sea movement. In contrast, the efficacy of alerting tools and the actors who can alert them are overestimated, as 44.7 % of the respondents think they should be alerted by sirens and 11.7 % by SMS, while such tools are not systematically present and rarely cover tsunami evacuation zones. And only 29.4 % correctly identify the official alert senders: mayors or prefectures. In contrast, 55.7 % declare they go high ground if they receive such instructions in one Alert SMS. The age, gender, residency status or location of the respondents explain a few differences in the collected data. However, relationships between tsunami risk and alert perceptions appear statistically not corelated. All the knowledge produced in this study finally might help the municipalities further develop awareness-actions and information on the tsunami, and inform what strategy they may apply in a short future to better increase the tsunami preparedness. [ABSTRACT FROM AUTHOR]

Tsunami hazard imposed by possible rupture of splay faults is important as it may significantly intensify tsunami heights locally. The Makran Subduction Zone (MSZ) in the northwestern Indian Ocean can generate large thrust earthquakes that could trigger significant tsunamis. In this paper, the effects of possible rupture of splay faults on the tsunami hazards of eastern MSZ are studied by developing a framework that uses stochastic earthquake rupture models and considers uncertainties related to rupture location, rupture geometry, seismic moment split ratio, earthquake slip asperity location within a fault plane, and earthquake slip heterogeneity. To quantify these uncertainties, 484 different parameter combinations of tsunami sources are considered systematically. The geometry of splay faults is developed using the most recent marine seismic surveys of the tectonic structure of the MSZ. A moment magnitude of 8.6 is considered as a scenario magnitude. The results of this study are generated in two parts, by considering average sources and stochastic sources. Results show significant local amplification of the maximum tsunami heights due to splay faults. For instance, the maximum wave height in Pasni, Pakistan can be amplified by a factor of four due to a single splay fault rupture scenario of average sources. [ABSTRACT FROM AUTHOR]

Tides 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. Plain Language Summary: Tsunami hazards can be evaluated using a probabilistic tsunami hazard assessment (PTHA) approach which determines probabilities of exceeding a certain tsunami intensity. A relevant source of uncertainty in PTHA are tides. Tsunamis striking the coast may have different impacts depending on whether they arrive at high or low tide. Moreover, the exposed infrastructure may last many decades and climate‐change‐driven sea‐level‐rise would compound tsunamis and tides, making the hazard worse. We develop two PTHA methods incorporating tides. The first method uses a stochastic reduced order model (SROM). The second method uses sets of tsunami simulations with same tide, known as collocation tidal phases. Both methods aim to estimate tsunami uncertainties and can be also used for non‐stationary probabilistic tsunami hazard assessment which combines tsunamis, tides and sea level rise (SLR). The new methods are applied into an illustration case in South China Sea. The method based on SROM is fastest solving the PTHA with tides. Though, the collocation‐based method is fastest solving for the nPTHA with tides and SLR. While the impact of tides is relevant in PTHA and nPTHA results, SLR produces a greater effect in the studied ports. The conclusions are site‐specific. Key Points: A Stochastic Reduced Order Model (SROM)‐based method and a collocation‐based method incorporating tides and sea level rise (SLR) are evaluated for tsunami hazard assessmentsThe collocation‐based method provides accurate results compared to the SROM‐based methodThe impact of tides and SLR on tsunami intensities depends on the tidal range and SLR within the exposure time, respectively [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Two‐decades of onshore‐offshore, ocean‐bottom seismometer, and passive‐source data are integrated to obtain high‐resolution 3‐D constraints on the architecture of the Nankai subduction zone. Our model reveals large along‐strike variability in the width of the outer‐forearc, with the crustal backstop (VP ≥ 5 km/s) extending within 50 km of Nankai Trough offshore Tokai and Kii Peninsula, but is a factor of 2 further landward (90–115 km) offshore Cape Muroto and Kyushu. The crustal backstop broadly coincides with the down‐dip extent of shallow slow‐earthquakes and the up‐dip extent of co‐seismic slip and geodetic locking, suggesting a link with the shallow frictional transition. In the inner‐forearc, high seismic‐velocities (VP > 6.6 km/s) in Kii Peninsula reflect Miocene plutons, impacting the nucleation and segmentation of large megathrust earthquakes. The complex geometry of the subducting slab drives spatial variability in the location of the down‐dip frictional transition. Variability in the width of the outer‐forearc, the dip of the subducting slab, and the depth distribution of deep slow‐slip events combine to produce large changes in the width of the seismogenic zone. This is most pronounced across Bungo channel, where the seismogenic zone narrows from 90 to 120 km in Shikoku to <60 km offshore Kyushu. Pinching of the seismogenic zone may explain the smaller area, and thus magnitude, of earthquakes offshore Kyushu and the reduction in slip‐deficit rate. Our results suggest crustal‐scale architecture is a key driver of profound along‐strike transitions in the location of frictional transition zones, and the width and slip behavior of the intervening seismogenic zone at Nankai Trough. Plain Language Summary: Some subduction zones produce the largest earthquakes and tsunami on Earth, while others slip aseismically. To understand what factors impact subduction zone slip behavior, we have integrated dense geophysical datasets that have accumulated over >20 years in SW Japan to construct the first high‐resolution, 3‐D image of an entire subduction zone. This image reveals large variability in the offshore extent of dense, rigid crustal rocks and suggests the position of this crustal backstop may influence the shallow transition from aseismic to seismic slip along the Nankai megathrust. The landward extent of seismic slip is also spatially variable and appears to be predominantly controlled by the geometry of the subducting plate. Collectively, along trench variability in the position of the crustal backstop (up‐dip transition) and the geometry of the subducting slab (down‐dip transition) combine to produce large variability in the width of the seismogenic zone. Earthquake magnitude is proportional to rupture area and pinching of the seismogenic due to the convergence of shallow and deep frictional transitions may explain the smaller magnitude of earthquakes offshore Kyushu. Our results reinforce the importance of crustal scale architecture in modulating earthquake and tsunami hazard at subduction zones. Key Points: Two‐decades of geophysical data suggest the crustal backstop coincides with the up‐dip transition from slow to seismic slip at Nankai TroughSpatial variability in backstop position and subducting slab geometry produce large changes in width of the seismogenic zone along‐strikePinching of the seismogenic zone between Shikoku and Kyushu may explain reductions in earthquake magnitude and slip‐rate deficit [ABSTRACT FROM AUTHOR]

The 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 mega thrust 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. [ABSTRACT FROM AUTHOR]

Quantitatively estimating combined storm surge and wave hazards provides scientific guidance for disaster prevention, mitigation, and relief in coastal cities. The marginal and copula functions are preferred based on the Kolmogorov–Smirnov test pass rate, and the relationship between storm surge and wave is quantitatively evaluated using the optimal function, then the bivariate risk probabilities are estimated. The results show that the generalized extreme value function and Gumbel copula function are suitable for fitting the marginal and joint distribution characteristics of the surge height and significant wave height in this study area, respectively. Second, the surge height shows an increasing trend closer to the coastline, and the significant wave height is higher further from the coastline. Third, when one variable is constant, the simultaneous, joint, and conditional risk probability tends to decrease as the other variable increases. In actual engineering design, improving the protection standard can effectively reduce the bivariate risk probability. In addition, we can estimate the optimal design criteria for different joint return periods by the constraint condition and objective functions. This study shows that the bivariate copula function can effectively evaluate the risk probability for different scenarios, which provides a reference for optimizing engineering protection standards. [ABSTRACT FROM AUTHOR]

Offshore Probabilistic Tsunami Hazard Assessments (offshore PTHAs) provide large-scale analyses of earthquake-tsunami frequencies and uncertainties in the deep ocean, but do not provide high-resolution onshore tsunami hazard information as required for many risk-management applications. To understand the implications of an offshore PTHA for the onshore hazard at any site, in principle the tsunami inundation should be simulated locally for every earthquake scenario in the offshore PTHA. In practice this is rarely feasible due to the computational expense of inundation models, and the large number of scenarios in offshore PTHAs. Monte Carlo methods offer a practical and rigorous alternative for approximating the onshore hazard, using a random subset of scenarios. The resulting Monte Carlo errors can be quantified and controlled, enabling high-resolution onshore PTHAs to be implemented at a fraction of the computational cost. This study develops efficient Monte Carlo approaches for offshore-to-onshore PTHA. Modelled offshore PTHA wave heights are used to preferentially sample scenarios that have large offshore waves near an onshore site of interest. By appropriately weighting the scenarios, the Monte Carlo errors are reduced without introducing bias. The techniques are demonstrated in a high-resolution onshore PTHA for the island of Tongatapu in Tonga, using the 2018 Australian PTHA as the offshore PTHA, while considering only thrust earthquake sources on the Kermadec-Tonga trench. The efficiency improvements are equivalent to using 4–18 times more random scenarios, as compared with stratified-sampling by magnitude, which is commonly used for onshore PTHA. The greatest efficiency improvements are for rare, large tsunamis, and for calculations that represent epistemic uncertainties in the tsunami hazard. To facilitate the control of Monte Carlo errors in practical applications, this study also provides analytical techniques for estimating the errors both before and after inundation simulations are conducted. Before inundation simulation, this enables a proposed Monte Carlo sampling scheme to be checked, and potentially improved, at minimal computational cost. After inundation simulation, it enables the remaining Monte Carlo errors to be quantified at onshore sites, without additional inundation simulations. In combination these techniques enable offshore PTHAs to be rigorously transformed into onshore PTHAs, with quantification of epistemic uncertainties, while controlling Monte Carlo errors. [ABSTRACT FROM AUTHOR]

The current diffuse-strain model of the collision between Africa and Eurasia in the western Mediterranean predicts a broad region with deformation distributed among numerous faults and moderate-magnitude seismicity. However, the model is untested because most deformation occurs underwater, at poorly characterized faults of undetermined slip. Here we assess the diffuse-strain model analysing two active offshore fault systems associated with the most prominent seafloor relief in the region. We use pre-stack depth migrated seismic images to estimate, for the first time, the total Plio-Holocene slip of the right-lateral Yusuf and reverse Alboran Ridge structurally linked fault system. We show that kinematic restoration of deformational structures predicts a slip of 16 ± 4.7 km for the Alboran Ridge Fault and a minimum of 12 km for the Yusuf Fault. Thus, this fault system forms a well-defined narrow plate boundary that has absorbed most of the 24 ± 5 km Plio-Holocene Africa-Eurasia convergence and represents an underappreciated hazard. Conventional models propose multiple fault systems across a diffuse deformation zone absorbing plate convergence in the western Mediterranean. Here the authors show new data supporting the active development of a single plate boundary fault system, representing an underappreciated seismic and tsunami hazard. [ABSTRACT FROM AUTHOR]

Tsunami source impacts in coastal areas should be investigated thoroughly; however, investigating the associated source uncertainties can incur large computational costs. This study presents a technique for rapid assessment of the impacts and their uncertainties based on a combination of the linear wave superposition for Green's functions and a static sweep algorithm for onshore terrain. A waveform from a tsunami source is quickly estimated at a shore based on the aforementioned superposition of single-point sources simulated by a linearized Boussinesq model. The maximum water surface elevation change in the waveform, the maximum tsunami elevation, is then determined. In addition, a digital elevation model for onshore terrain that can be inundated by a tsunami is scanned using the sweep algorithm to statically compare the tsunami and ground elevations. As a result, areas with lower ground elevation than the tsunami are quickly identified as potential tsunami hazard zones. This combined analysis is applied to assess potential tsunami sources in the Japan Sea, and the source impacts are comprehensively investigated for Sakata and Akita cities in Japan. Our analysis successfully and quantitatively indicates source impacts while considering their great uncertainty. Additionally, critical areas for expanding tsunami inundation are quickly and efficiently identified. [ABSTRACT FROM AUTHOR]

Coastal areas of Indonesia that are close to tectonic plates are vulnerable to earthquakes and generated tsunamis. The Munjungan Coast South of East Java-Indonesia is such a vulnerable tsunami area. This coastal area, besides being close to tectonic plate boundaries, has the shape of an open bay which makes it particularly vulnerable to tsunami impacts and, therefore, in need of strict disaster mitigation measures. Assisted Geographic Information System (GIS) applications with map overlay techniques and by the Arc View 3.3 software program can help in the taking of measures that can reduce the impact of tsunami hazards. The processed product of the GIS methodology in the form of a tsunami hazard zoning map, as well as designated evacuation route maps, can be helpful tools in tsunami impact mitigation, when a significant and potentially tsunamigenic earthquake occurs. The present study used a survey method and area sampling to obtain a better understanding of the public’s perceptions and attitudes in responding more effectively to the potential of tsunami disasters. Based on the interpretation of the zoning map for the classification of disasterprone areas and route maps for evacuation, four villages were identified as being more prone to tsunami disasters. The condition of the population in these four disaster-prone villages, despite their higher level of knowledge about tsunamis, was not followed by their perceptions and proper attitudes towards mitigating the potential danger. People on the coast of Munjungan did not appear to be particularly concerned about the tsunami hazard. [ABSTRACT FROM AUTHOR]

Many bridges that lie within possible tsunami inundation zones are critical links in transport networks. Some efforts have been made to determine the effects of tsunamis on bridges, but only a limited range of published design guidelines are available. Therefore, it is necessary to further investigate the effects of tsunamis on bridges. In the current study, physical modeling experiments were carried out to measure bore impact forces and pressures for various tsunami bore strengths on a bridge deck with different abutment types (wing wall and spill-through) and different opening and submergence ratios. The experiments were conducted in a wave flume with dimensions of 14 × 1.2 × 0.8 m (length × width × height), equipped with an automatic gate designed to generate a tsunami bore. The horizontal and vertical forces showed an increasing trend with increasing submergence ratio for both types of abutment. However, the horizontal force showed a decreasing trend as the opening ratio decreased, while the vertical force initially increased as the opening ratio decreased, until it reached a peak value, and then it started to decrease. The overall shapes of the results for both types of abutment are similar, with higher values for spill-through abutments due to their lower energy dissipation rates. Based on the experimental data, empirical equations are proposed for estimation of tsunami loads as a function of opening and submergence ratios. [ABSTRACT FROM AUTHOR]

Copyright of Mugla Journal of Science & Technology is the property of Mugla Journal of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The potential of a full-margin rupture along the Cascadia subduction zone poses a significant threat over a populous region of North America. Previous probabilistic tsunami hazard assessment studies produced hazard curves based on simulated predictions of tsunami waves, either at low resolution or at high resolution for a local area or under limited ranges of scenarios or at a high computational cost to generate hundreds of scenarios at high resolution. We use the graphics processing unit (GPU)-accelerated tsunami simulator VOLNA-OP2 with a detailed representation of topographic and bathymetric features. We replace the simulator by a Gaussian process emulator at each output location to overcome the large computational burden. The emulators are statistical approximations of the simulator's behaviour. We train the emulators on a set of input–output pairs and use them to generate approximate output values over a six-dimensional scenario parameter space, e.g. uplift/subsidence ratio and maximum uplift, that represent the seabed deformation. We implement an advanced sequential design algorithm for the optimal selection of only 60 simulations. The low cost of emulation provides for additional flexibility in the shape of the deformation, which we illustrate here considering two families – buried rupture and splay-faulting – of 2000 potential scenarios. This approach allows for the first emulation-accelerated computation of probabilistic tsunami hazard in the region of the city of Victoria, British Columbia. [ABSTRACT FROM AUTHOR]

Solitary wave is often used to simulate tsunami propagating in deep water and breaking solitary wave is often used to simulate tsunami bore propagating in shallow water or on land. The breaking solitary wave force on box-girder, which has been widely used in bridge engineering in coastal areas of China, receives few attentions. This study aims to investigate characteristics and generation mechanism of breaking solitary wave force on box-girder numerically. A numerical wave flume with a 1:20 slope was built firstly, then the solitary wave generation ability, wave deformation and wave breaking on the slope, as well as wave force calculation precision, are validated. The water depth 0.6 m, the slope gradient 1:20 and the distance between slope top and box-girder 2.0 m remain unchanged, while the wave height and clearance changes in different cases. The time histories of horizontal force and vertical force on box-girder can be divided into three and four stages respectively according to their characteristics. The surface of box-girder is decomposed into a series of panels to facilitate exploring tsunami bore force generation mechanism. Results show horizontal force is dominated by static pressure on upstream vertical panels and vertical force is mainly contributed by static pressure on upstream horizontal panels and on panels in the chambers. Tsunami bore overtopping the box-girder deck impacts the top panel vigorously and results in the peak value of negative vertical force. [ABSTRACT FROM AUTHOR]

Unmanned Aerial Vehicles (UAV) are widely used in disaster relief and road exploration in recent years. This paper mainly studied the emergency response of UAVs after disasters. The UAV response system is mainly suitable for the distribution of necessities and road exploration after geological disasters and tsunamis in coastal areas. By analyzing the problem and making reasonable assumptions, the optimization model was established with the traffic planning theory, and MATLAB software was used to program and solve the problem. An optimal scheduling scheme was presented to solve these problems. The normalization method was used to select a highly capable UAV. Taking the minimum volume of idle space buffer material as the objective function and taking into account the constraints, such as payload of unmanned aerial vehicle, a single objective programming model was established. The results are as follows: Each International Standards Organization (ISO) cargo container has five UAVs B, one UAV C, one UAV F and one UAV H. It provides 188 days of relief requirements with ISO cargo containers' space utilization of 71.4%. The research shows that the UAV response system has the functions of necessities distribution and road exploration after disasters, and can be used to deal with the emergency response after disasters in coastal areas, and has a wide range of applicability. [ABSTRACT FROM AUTHOR]

The amount of disaster waste is one of the most important performance indicators in quantifying the resilience of a community. In fact, disaster waste can have significant negative impacts on the environment in affected regions and hinder the postdisaster recovery process. Appropriate disaster waste management should be developed in Japan before the occurrence of the Nankai Trough earthquake. It is expected that the seismic and tsunami intensities caused by the anticipated Nankai Trough earthquake will be substantially larger than those caused by the 2011 Great East Japan earthquake. In this paper, a risk‐based methodology is presented for estimating the amount of disaster waste generated by both the ground motions and the tsunami due to the anticipated Nankai Trough earthquake. First, Monte Carlo simulation‐based probabilistic hazard analyses are performed to obtain seismic and tsunami hazard curves considering the uncertainty associated with fault movement along the Nankai Trough. Structural damage data associated with past earthquakes are used to develop seismic and tsunami fragility curves. The amount of disaster waste generated from a single structure is defined as the generation unit and is determined based on past disasters. Finally, with the aid of a geographic information system, the risk of disaster waste can be estimated using the hazard and fragility curves and the generation units. As an illustrative example, the risk curves and expected values associated with disaster waste in Mie Prefecture, Japan, are estimated based on the proposed framework. [ABSTRACT FROM AUTHOR]

Fault coupling is vital in determining the amount of strain that is accumulated along faults. The magnitude and location of stored elastic strain energy in highly coupled regions has important implications for understanding the full range of slip behavior at plate boundary faults, as well as earthquake and tsunami hazards. We use the temporary dense amphibious array of seismometers offered by the Cascadia Initiative to create a high‐resolution catalog of events to examine the spatio‐temporal behavior of earthquakes near the plate interface. The data show that in southern Cascadia the plate interface updip of the geodetically locked region is nearly devoid of seismicity, therefore likely highly coupled and accumulating strain. The catalog reveals events that are clustered at the downdip edge of the highly coupled megathrust that correlate in time with nearby strain transient observations. Template matching of events in the cluster using permanent stations of the Northern California Seismic Network over a 10‐year period between 2010 and 2020 indicates that this cluster is unique in space and time. Its activity only during the strain transient provides support for the utility of seismic observations in the identification of strain transients. Plain Language Summary: Great megathrust earthquakes have occurred in the Cascadia Subduction Zone. The most recent occurred in 1700, and it is expected that another will happen in the next few hundred years. Although the megathrust has hosted great earthquakes, few small interplate events have been identified along this plate boundary. Instead, a portion of the convergence between the tectonic plates is released in both periodic slow slip events and (quasi) continuous fault creep. It is essential to understand the full range of plate boundary behavior to assess the hazard risk for great earthquakes. To further this understanding, we gather data using a densely spaced temporary array of seismometers deployed in southern Cascadia in 2014–2015 to increase detection as well as determine precise earthquake locations. We identify events that are on or very near the plate boundary fault. There is some clustering of earthquakes near the plate boundary, but we find an absence of earthquakes along the shallowest segment, that indicate that the fault is likely locked. When compared to other geophysical observations in the area, it appears that the cluster of earthquakes near the plate boundary is sensitive to strain transients, demonstrating the utility of seismic observations in investigating these phenomena. Key Points: Catalog creation of 1,452 events in southern CascadiaLack of shallow offshore plate interface seismicity suggests locally high couplingTemplate matching of plate interface events reveals a cluster of seismicity sensitive to long‐term plate interface strain transients [ABSTRACT FROM AUTHOR]

Current stochastic rupture modeling techniques do not consider the potential influence of inter‐seismic coupling, a first‐order property of a megathrust, which can show correlation between areas of high coupling and areas of greater slip as seen in recent large ruptures globally. Therefore, it is reasonable to assume that it should be considered as prior information in rupture modeling. Here, we first present a mathematical formalism to introduce coupling models as prior information into stochastic rupture modeling. We then focus on how introducing slip deficit information into the stochastic rupture models influences slip distributions for the Cascadia subduction zone (CSZ). We compare rupture models created with two end member models of coupling, one with a shallow coupling and another with coupling deeper downdip. We also discuss the comparison to models created without assuming knowledge of the coupling distribution except for variation in the downdip limit of slip. Variations occur and correlate well with areas with the largest differences in slip deficit rates. The ruptures are then used for regional probabilistic tsunami hazard assessment. Overall, the tsunami amplitudes generated are much more hazardous in the northern extent of the CSZ where differences in coupling distribution are more prevalent. Models obtained from assuming a shallower downdip limit have tsunami amplitudes more similar to those from the geodetic coupling models. Although uncertainties are present in the accuracy of coupling, imposing either constraint created different hazard estimations when compared to those where no prior coupling information was used. Plain Language Summary: Uncertainties are often present when trying to determine future earthquake rupture potentials and their associated hazards. We present here a means of including a first‐order property of a megathrust, a fault's pattern of the current ability to slip (coupling), in a current rupture modeling technique often applied to hazard assessments. We model ruptures classes constrained by two different coupling models for the Cascadia subduction zone (CSZ), as well as two other classes without imposed coupling. These ruptures are then used to determine associated tsunamis and the total probabilistic tsunami hazards for the Cascadia region. Overall, the tsunami amplitudes generated are much more hazardous in the northern extent of the CSZ where differences in coupling distribution are more prevalent. Models obtained without coupling but constrained by a shallower limit of slip have tsunami amplitudes more similar to those from the geodetic coupling models. Although uncertainties are present in the accuracy of coupling, imposing either constraint created different hazard estimations when compared to those where no prior coupling information was used. Key Points: Including fault coupling produces considerable variations for stochastic slip rupture models as well as the resultant probabilistic tsunami hazardsThe coupling models produced similar patterns of tsunami hazards for the central Cascadia region and more dissimilar hazards in the northern and southern coastal Cascadia regionsExpanding seafloor observations is necessary for a more accurate understaning of the Cascadia tsunami hazard [ABSTRACT FROM AUTHOR]

This paper describes an integrated climatological‐hydrodynamic method that couples probabilistic hurricane model, storm surge model, inundation model, coastal protection data, and sea level rise projections to estimate tropical cyclone‐induced coastal flood inundation hazard in a coastal megacity‐Shanghai, China. We identify three "worst‐case" scenarios (extracted from over 5,000 synthetic storms) that generate unprecedentedly high flood levels in Shanghai. Nevertheless, we find that the mainland Shanghai is relatively safe from coastal flooding under the current climate, thanks to its high‐standard seawall protection. However, the city is expected to be increasingly at risk due to future sea level rise, with inundation two times and 20 times more likely to occur by mid‐ and late‐21st century, respectively, and inundation depth and area to greatly increase (e.g., 60%–1,360% increase in the inundation area for the "worst cases" by 2,100). The low‐lying and poorly protected area (e.g., Chongming Island) is likely to be moderately affected by flood events with long return periods at the current state but could be largely inundated in future sea‐level‐rise situations. Plain Language Summary: Coastal flooding associated with tropical cyclones (TCs, also called typhoons in the Northwest Pacific Basin) is often the most devastating and costliest of natural hazards. Struck by a number of strong TCs in recorded history, Shanghai may be highly vulnerable to coastal flooding due to its location within the Yangtze River delta, low‐relief topography and high‐density population. However, given the limited historical data, observation‐based analysis is insufficient to capture the potential extreme events. In this study, we use a synthetic storm model to generate large numbers of TC events that are physically plausible but may have never occurred in the past. Storm tide and the resultant coastal flooding induced by each TC are further simulated with a coupled circulation‐inundation model. Results suggest that Shanghai may encounter extreme storm tide flooding with very low possibilities under the current climate condition. With the protection of seawall, the city is generally immune to extensive flooding, except the low‐lying and poorly protected coastal floodplain and estuarine island, Chongming. However, future sea level rise will induce a significantly increased flood risk in Shanghai over the 21st century. Key Points: An integrated statistical‐hydrodynamic method is developed to estimate tropical cyclone‐induced coastal flood inundation hazardThe mainland Shanghai is found to be well protected by high‐standard seawalls under current climateHowever, without further improvement in the protection, Shanghai is expected to be increasingly at risk due to future sea level rise [ABSTRACT FROM AUTHOR]

This study presents an innovative probabilistic tsunami inundation assessment for an earthquake scenario to randomly generate tsunami inundation depth distributions by quantitatively evaluating the spatial correlation of tsunami inundation depths using singular value decomposition (SVD) derived from proper orthogonal decomposition and to evaluate the tsunami inundation depths considering the imminent occurrence of an earthquake. We found a good agreement between the evaluation results of the proposed surrogate model and the numerical results of the nonlinear long wave equations for the tsunami inundation depth distribution in Kamakura city, Japan, due to the Sagami Trough megathrust earthquake. Evaluating the spatial correlation using SVD has the advantage that the covariance matrix does not need to be defined in advance but can be defined from the data itself. We also achieved a significant reduction in the number of required tsunami propagation simulations for the probabilistic assessment and attained higher computational efficiency by extracting spatial correlations with SVD. Furthermore, we conducted a probabilistic tsunami inundation assessment focusing on a relatively short period (i.e., 50 years) considering the time‐dependent occurrence probability of the target earthquake. The proposed probabilistic assessment method with mode decomposition is applicable to the general probabilistic tsunami hazard assessment by integrating it with physical stochastic slip models. Plain Language Summary: This study proposes an innovative method to evaluate the probabilistic tsunami inundation area on land considering the imminence of an earthquake occurrence. Generally, the computational cost associated with evaluating the probabilistic tsunami inundation area is high because it is necessary to consider all possible uncertainties. In this study, we apply a singular value decomposition method to a small number of inundation depth distributions to extract the characteristics of these distributions. As a result, we are able to evaluate the probabilistic tsunami inundation depth in a future 50‐year period using a small number of inundation depth distributions. Key Points: The singular value decomposition is used to evaluate the eigenmodes of the tsunami inundation depth and reduce the computational costThe variations in three variables are considered earthquake fault uncertainties: the fault depth, slip amount, and slip distributionA time‐dependent probabilistic tsunami inundation assessment is performed with the Brownian passage time distribution to account for seismic imminence [ABSTRACT FROM AUTHOR]