Search

The Nankai-Tonankai megathrust earthquake and tsunami pose significant risks to coastal communities in western and central Japan. Historically, this seismic region hosted many major earthquakes, and the current national tsunami hazard assessments in Japan consider megathrust events having moment magnitudes between 9.0 and 9.1. In responding to the lack of rigorous uncertainty analysis, this study presents an extensive tsunami hazard assessment for the Nankai-Tonankai Trough events, focusing upon the southwestern Pacific region of Japan. A set of 1,000 kinematic earthquake rupture models is generated via stochastic source modelling approaches, and Monte Carlo tsunami simulations are carried out by considering high-resolution grid data of 10-m and coastal defense structures. Significant advantages of the stochastic tsunami simulation methods include the enhanced capabilities to quantify the uncertainty associated with tsunami hazard assessments and to effectively visualize the results in an integrated manner. The results from the stochastic tsunami simulations can inform regional and local tsunami risk reduction actions in light of inevitable uncertainty associated with such probabilistic tsunami hazard assessments, and complement conventional deterministic tsunami scenarios and their hazard predictions, such as those developed by the Central Disaster Management Council of the Japanese Cabinet Office. [ABSTRACT FROM AUTHOR]

The estimate of an individual wave run-up is especially important for tsunami warning and risk assessment, as it allows for evaluating the inundation area. Here, as a model of tsunamis, we use the long single wave of positive polarity. The period of such a wave is rather long, which makes it different from the famous Korteweg–de Vries soliton. This wave nonlinearly deforms during its propagation in the ocean, which results in a steep wave front formation. Situations in which waves approach the coast with a steep front are often observed during large tsunamis, e.g. the 2004 Indian Ocean and 2011 Tohoku tsunamis. Here we study the nonlinear deformation and run-up of long single waves of positive polarity in the conjoined water basin, which consists of the constant depth section and a plane beach. The work is performed numerically and analytically in the framework of the nonlinear shallow-water theory. Analytically, wave propagation along the constant depth section and its run up on a beach are considered independently without taking into account wave interaction with the toe of the bottom slope. The propagation along the bottom of constant depth is described by the Riemann wave, while the wave run-up on a plane beach is calculated using rigorous analytical solutions of the nonlinear shallow-water theory following the Carrier–Greenspan approach. Numerically, we use the finite-volume method with the second-order UNO2 reconstruction in space and the third-order Runge–Kutta scheme with locally adaptive time steps. During wave propagation along the constant depth section, the wave becomes asymmetric with a steep wave front. It is shown that the maximum run-up height depends on the front steepness of the incoming wave approaching the toe of the bottom slope. The corresponding formula for maximum run-up height, which takes into account the wave front steepness, is proposed. [ABSTRACT FROM AUTHOR]

The Italian Tsunami Alert Centre of the Istituto Nazionale di Geofisica e Vulcanologia (Centro di Allerta Tsunami, hereinafter CAT-INGV) supported a computer-assisted telephone interview (CATI) survey to investigate tsunami risk perception in two pilot regions of southern Italy. The survey was carried out on a stratified sample of 1021 interviewees representing about 3.2 million people living in 183 coastal municipalities of the two regions, namely Calabria and Apulia. The main goal of this research is to verify whether and how people's perception of tsunami hazard compares to the results of (PTHA) – probabilistic tsunami hazard assessment (TSUMAPS-NEAM project; Basili et al., 2018). As shown by the results of this project, both investigated regions are characterised by high tsunami hazard. Nonetheless, the long return time of such events could lead people to consider the occurrence of a tsunami in the Mediterranean Sea to be very unlikely. The survey results reveal that people's risk perception is low: for almost half of the whole sample the occurrence of a tsunami in the Mediterranean Sea is considered quite unlikely, with a clear difference between Apulia and Calabria. In the latter region the risk perception is much higher than in the former, probably due to the shorter time elapsed since the last event. Also, belonging to different coastal areas For the purposes of this paper, the term "coastal area" refers to the part of the coastline defined by both seas and regions' limits, according to current geographical conventions. Tyrrhenian Calabria indicates the coastal region between the municipalities of Tortora and Scilla, Ionian Calabria spans from Reggio Calabria to Rocca Imperiale; Ionian Apulia from Ginosa to Castrignano del Capo, and Adriatic Apulia from Gagliano del Capo to Chieuti. appears to have a significant influence on the way tsunami hazard is conceived, having a stronger effect on risk characterisation: the interviewees of Tyrrhenian Calabria are indeed more likely to associate tsunami risk with volcanoes than the Ionian citizens. This is coherent considering the presence of active volcanoes and related tsunami precedents in the Tyrrhenian. Television emerged as the most relevant source of knowledge for almost 90 % of the sample, and the influence of media also results in the way tsunami risk is characterised. In particular, the survey showed that people's perception and understanding of tsunamis are affected by media accounts of large events, such as the 2004 Sumatra and the 2011 Japan tsunamis. At the same time, it is evident that the risk posed by smaller events is underrated. Furthermore, the survey's results show that the word "tsunami" occupies a different semantic space in comparison to the Italian traditional headword maremoto , with differences among sample strata. In other words, the same physical phenomenon would be understood in two different ways by younger, educated people and elders with a low education level. The results of this study, although limited to two regions, provide a first assessment of tsunami risk perception in Italy, also entailing important consequences for both risk communication practice and mitigation policies. [ABSTRACT FROM AUTHOR]

This study presents the first tsunami scenario database in Marmara Sea, Turkey referring to 30 different earthquake scenarios obtained with the combinations of 32 possible fault segments. The fault mechanisms in Marmara Sea have been studied in detail within FP-7 MARSite project, which were derived from various databases and literature review. Tsunami simulations have been performed according to these defined 30 earthquake scenarios by tsunami numerical code NAMI DANCE (NAMIDANCE, 2011) which solves Nonlinear Shallow Water Equations (NLSWE) using leap-frog scheme. For each earthquake scenario, tsunami hydrodynamic parameters, mainly maximum water surface elevations, arrival time of first wave and maximum wave, and water level fluctuations were calculated at 1333 synthetic gauge points meticulously selected along the coasts of Marmara Sea. The overall simulation results indicate that maximum expected wave heights due to these earthquake scenarios are between 1 m and 2 m and even more than 2 m at some locations along Marmara coasts, such as Kadikoy, Halic and Silivri coasts in Istanbul and Bayramdere and Kursunlu districts along the coasts of Bursa province. The estimated maximum water levels at Bostanci, Pendik and Buyukada coasts in Istanbul, Cinarcik and Bandirma towns and at the entrance of Izmit Bay would reach up to 2 m. Tekirdag coasts and Buyuk Cekmece and Bakirkoy coasts in Istanbul and Yalova coasts would experience maximum tsunami wave amplitudes around 1.5 m. The waves reach up to 1 m at Izmit and Gemlik Bays, Erdek Peninsula and Marmara Island. The overwiew of the results reveal that higher historical tsunami wave heights observed in Marmara Sea cannot be explained by only earthquake-generated tsunamis. Therefore, there is strong agreement on considering submarine landslides as the primary tsunami hazard component in the Marmara Sea as experienced during history and expected in the future. [ABSTRACT FROM AUTHOR]

This study visualized the spatio-temporal changes in the tsunami inundation area and analyzed its expansion mechanism. The most characteristic of the Great East Japan Earthquake is the damage caused by the tsunami. And 90% of the dead was caused by it. One of the factors is that the preparation of countermeasures corresponding to the huge tsunami was not fully prepared. Therefore, after the Great East Japan Earthquake, the Japanese government has emphasized the importance of the advance preparation of the hugest tsunami expected. According to the past experience the occurring of huge tsunami is very rare. Earthquake researchers have observed same scale tsunami in every 1000 years in Japan. According prediction, next huge tsunami may be happened around the 2030. Therefore, analyzing the tsunami inundation mechanism of the Great East Japan Great Eastern is important for the future tsunami countermeasure. The arrival time and spatial distribution of tsunami inundation can be considered as a main important component of evacuation planning. In addition, a wide range of inundation area caused by huge tsunami is suitable for analyzing the inundation mechanism compared with a small-scale tsunami inundation. In this study I would like to examine the tsunami inundation process caused by the Great East Japan Earthquake in 2011. The method is as follows. First, movies shooting the tsunami inundation are collected from DVDs and TV hosting services. And they are examined as analysis materials. As a result, movies that taken from the ground were impossible to shoot the dynamic process of tsunami flooding. So that movies that taken from the helicopter or airplane was selected in this research. Next, the movies are converted into images at regular intervals of time. And adding position information to images (geo-reference), images are imported on the geographic information system (GIS). After that, Inundation limit lines are digitized. In this study, inundation limit lines are created at intervals of around 5 seconds. However, when the image is disturbed by dust etc., images of around 5 seconds are used. Basic information on the tsunami inundation handled in this study is shown in Table 1 and Figure 1. As the result, tsunami inundation process was strongly affected by the location of buildings (Figure 2). On the other hand, the inundation distance declined even where the fields spread. The spatio-temporal variation of the inundation process was quantitatively clarified. Regression analysis was performed with variables of inundation time and inundation distance. As a result, changes in correlation were observed in a certain section. In order to analyze the factors, two regression analyses were conducted. First is the inundation time and elevation as variables. Second is the inundation time and distance from buildings as variables. The building data had acquired the image before the earthquake (April 4, 2010) from Google Earth, and created the building shape data. As a result of each analysis, it became clear that sections where the elevation suddenly changes and the short distance from buildings, overlapped sections where the inundation distance does not extend (Figure 3). These results suggest that it is possible to predict inundation time and distance in other areas if parameters can be acquired. [ABSTRACT FROM AUTHOR]

The FORMOSAT-3/COSMIC (F3/C) radio occultation (RO) technique vertically scans the atmosphere from 0 to 800 km altitude over eastern Asia and the Pacific Ocean during the 2011 Mw9.0 Tohoku earthquake and tsunami. The mean wavelet spectra derived from dozens of atmospheric and ionospheric RO sounding profiles within ten hours after the earthquake illustrate that the atmospheric oscillations with a vertical wavelength ranging from 0.5 to 8 km and from 10 to 40 km, respectively, appear in the stratosphere and ionosphere within 6 hours after the earthquake initial rapture. The vertical wavelength estimated from the atmospheric gravity wave dispersion relation is compared with the observed vertical wavelength. The small-scale gravity waves may not be easy to reach the upper ionosphere. These RO-observed long-lasting atmospheric and ionospheric oscillations may consist of the earthquake/tsunami wavefront and its residual oscillatory tail. The results suggest that the RO technique is a powerful tool which is suitable for probing earthquake/tsunami-induced oscillations in the atmosphere, and allow a more comprehensive understanding of the excitation, propagation, and dissipation of earthquake/tsunami-induced gravity waves in the entire atmosphere. [ABSTRACT FROM AUTHOR]

Although interseismic locking distributions have been used in qualitatively evaluating the future earthquake potential, quantitatively estimating how an earthquake may rupture through the locked interface is a more useful tool for quantifying both seismic and tsunami hazards. Here, we investigate rupture scenarios from interseismic locking models along the megathrust interface below Nicoya peninsula, Costa Rica using spontaneous rupture simulations. We first estimate initial stress from locking, then initiate spontaneous ruptures at different nucleation points and observe the eventual earthquake magnitudes and slip distribution. We find that ~40% of nucleations tested develop into large earthquakes of Mw>7.2 based on present interseismic locking models. Of these events, those nucleated from deeper depths have a tendency for larger-amplitude shallow slip, suggesting increased tsunami potential. Furthermore, irrespective of the input locking models we do not observe rupture scenarios of earthquakes with intermediate magnitudes between 6 and 7, a result consistent with observations outside of the aftershock period in Nicoya. The results of hypocentre-dependent earthquake magnitudes and tsunamigenic potential not only pose challenges in estimating rupture extents from locking models, but also underscore the significance of quantitatively evaluating seismic and tsunami hazard in subduction zones. [ABSTRACT FROM AUTHOR]

On September 28, 2018, a magnitude Mw 7.5 earthquake occurred in the neck of Sulawesi's Minahasa peninsula. The combined effects of the earthquake and tsunami caused catastrophic damage and more than 2000 deaths. An international tsunami survey team (ITST) was deployed 3 weeks after the event to document flow depths, runup heights, inundation distances, sediment deposition, damage patterns at various scales, performance of the man-made infrastructure and impact on the natural environment. The 23 to 29 October ITST covered a 100 km stretch of coastline circling the entire Palu Bay and adjacent coastlines along the Makassar Strait. A 200 km long reconnaissance flight with an Indonesian Army Mil Mi-17 helicopter provided oblique aerial photography of impacted sites. The collected field survey data includes 130 tsunami runup and flow depth measurements. The tsunami impact peaked inside Palu Bay with flow depths above ground reaching 6 m and maximum runup heights exceeding 10 m. Inundation and tsunami damage was mostly limited to within 0.5 km of the shoreline except along rivers. A rapid decrease of tsunami heights was observed towards the bay entrance and outside of the Palu Bay along the Makassar Strait coastlines. Two tsunami eyewitness video recording locations inside Palu Bay were surveyed for subsequent video image calibration, tsunami hydrograph and flow velocity analysis. We deployed a Leica BLK360 scanner from the NHERI RAPID facility. We acquired precise topographic data using terrestrial laser scanning (TLS) at selected video sites with multiple scans acquired from different instrument positions. These ground-based LiDAR measurements produce 3-dimensional "point cloud" datasets. Digital photography from 3 scanner-mounted cameras yields full dome panoramic images overlaid on highly accurate point clouds. The main coastal road in Palu was overwashed with flow velocities of more than 7 m/s. Field observations, drone videos, helicopter and satellite imagery are presented. Eyewitnesses interviewed based on established protocols indicate rapid tsunami arrivals within a few minutes of the earthquake. We educated residents about tsunami hazards as community-based education and awareness programs are essential to save lives in locales at risk from locally generated tsunamis. [ABSTRACT FROM AUTHOR]

The east coast of Tasmania is directly exposed to tsunamis originating from the Puysegur subduction zone, and would be affected approximately 90 minutes post-earthquake. Tasmania does not experience tsunamis frequently, and tsunami hazard is poorly understood and planned for in the state. Moreover, the risk to Hobart port operations from a large tsunami has not previously been considered. This study applied numerical modelling to simulate the effects of a maximum credible tsunami (Mw 8.7 earthquake of New Zealand's southwest coast, combined with a highest astronomical tide), with the aim of determining potential coastal inundation levels, and assessing risks to shipping operations in Hobart Port. Inundation modelling was performed using the ANUGA hydrodynamic library, together with a detailed terrain model constructed from LiDAR and bathymetric datasets. In addition, a dune erosion operator was written for ANUGA, to account for tsunami erosion of the sand dunes in front of affected areas. The maritime hazard assessment focused on tsunami impacts for shipping in the navigation channel and ports, including mobilisation and evacuation times required for specific vessel types that frequent the harbour. Modelling results show a maximum incoming tsunami wave of approximately 7 m in exposed coastal areas, which could lead to inundation depths of > 4 m in some places. Significant seiching and wave reflections are evident in Hobart's main channel and embayments, which would pose a considerable risk to marine craft. An important finding of this study is that the feasibility of shipping evacuation from Hobart port is questionable, given the timeframes involved and the nature of simulated water disturbance. This study demonstrates the use of numerical modelling to inform tsunami hazard assessment, and highlights an often overlooked aspect of tsunami hazard. Statewide emergency management plans are currently being updated to make use of this work. [ABSTRACT FROM AUTHOR]

Marine tsunamis have been increasingly discussed in the context of ocean-wide natural hazards since the 2004 Sumatra, the 2011 Tohoku earthquake and the more recent 2018 Palu tsunamis. However, as historical reports and recent studies have shown, tsunamis also occur in lakes. While ocean tsunamis are often caused by earthquake-related plate displacements, tsunamis in lakes are of seismic or aseismic origin, caused by mass-movement processes that displace large amounts of water, generating devastating waves. In Switzerland, historical reports document that tsunamis occurred in many lakes (e.g. 563 AD in Lake Geneva, 1601 and 1687 AD in Lake Lucerne) causing large damages and casualties. The causes of these historical tsunamis were diverse and include earthquake-triggered sublacustrine and subaerial mass-movements, spontaneous delta collapses. Today, the shorelines of many Swiss lakes are densely populated. Although tsunamis are known to have occurred in the past on various Swiss lakes, a workflow for a holistic tsunami hazard assessment is still missing. An interdisciplinary project, funded by the Swiss National Science Foundation, uses the outstanding field laboratory of Switzerland's lakes to better understand the key concepts of governing processes of lake tsunamis by investigating i) their trigger mechanisms, ii) the geotechnical and sedimentological properties of the unstable sediment, iii) the potentially unstable sediment volumes on charged slopes, iv) wave propagation and inundation, v) onshore tsunami deposits and vi) their related hazard. The results of this project will provide the basis for assessing the risk for people and infrastructure along lakeshores and coasts. [ABSTRACT FROM AUTHOR]