Extreme Tsunami Research Articles

Traditional and Non-Traditional Approaches to Prediction of Natural Catastrophes

The catastrophes number from begin of XXI century increased about two times. The causes of the fact appeared to be obscure, but some suggestions based on understanding space and global processes, exists. The most terrible phenomena are tsunami. Such a wave got death of 700 000 people in 2004. A new tsunami got South West Asia in the end of 2018. Biological indications and understanding of some phenomena connected with natural life is a way toward prediction of tsunami. Living organisms are able to predict some future events particular catastrophic incidents. This is adaptive characters producing by evolution. The more energy produces incident the more possibility to predict one. Wild animals escaped natural hazards including tsunami (e.g. extreme tsunami in Asia December 2004). Living animals are able to predict strong phenomena of obscure nature. For example, majority of animals escaped Tungus catastrophe taking place in Siberia at 1908. Wild animals are able to predict nuclear weapon experiences. The obscure characters are not typical for human, but they are fixed under probability 15%. Effective theory describing such a character are absent till now. Russian scientist N.Kozyrev suggested existence of unknown physical field (but gravitation and electro-magnetic). The field was named “time” or “chrono”. Some characters of the field appeared to be object of physical experiment. Kozyrev suggested specific role of the field for function of living organisms. Transition of biological information throw space (telepathy) and time (proscopy) may be based on characters of such a field. Hence physical chrono-and-information field is under consideration. Animals are more familiar with such a field than human. Evolutionary process experienced with possibility of extreme development of contact with such a field using highest primates. Some equipment of detection of such a field is in progress. The perspective way for study of mysterious phenomena of physic is researches of this field characters.

TSUNAMI MODELLING IN A BUILT-IN COASTAL ENVIRONMENT WITH ADAPTIVE MESH RIFINEMENT AND VARYING BOTTOM FRICTION

The great Japan earthquake on March/11/2011provoked an extreme tsunami wave toward the northeastern Japanese coast. The tsunami inundation covered a wide range of territories stretching over 500 km2 and caused devastating influences that claimed more than 15,000 lives (Mori et al. (2011)). Miyagi Prefecture, the closest mainland to the epicentre, received massive tsunami waves that reached over 40 m in run-up height. Prasetyo et al. (2019) aimed to reproduce the tsunami wave inundation in Onagawa Town of Miyagi Prefecture by building a physical model using Hybrid Tsunami Open Flume in Ujigawa Open Laboratory (HyTOFU) at Kyoto University to study the inundation process by measuring the wave height and arrival time. For that purpose, two wave types were used, the (Pump-type) hydraulic bore, and the (Piston-type) solitary wave. Also, 2D and quasi-3D (Q3D) models were tested for their robustness and applied to emulate tsunami propagation in the complex coastal city model. In this study, we adopted adaptive mesh refinement (AMR) for its efficiency in tsunami modelling with Basilisk open-source flow solver for non-linear shallow water (Saint-Venant) equations and fully non-linear Boussinesq (Green-Naghdi) equations (Popinet (2015)). The numerical experiment was conducted to validate the model by comparing the wave height with the physical model experiment, the 2D, and Q3D model results by Prasetyo et al. (2019).

Relationship between Coastal Hazard Countermeasures and Community Resilience in the Tōhoku Region of Japan Following the 2011 Tsunami

Many coastal communities around the world that are vulnerable to inundation from tsunamis or storm surges are investing significant resources into countermeasures such as seawalls, levees, and breakwaters to limit damage from such events. A potential framework for studying the relationship between coastal hazard countermeasures and their impact on community resilience is proposed in this investigation and is applied to 27 coastal cities in the Tōhoku region of Japan following the 2011 tsunami. Community resilience was quantified using a modified version of the resilience inference measurement (RIM) method in which parameters of intensity, exposure, damage, and recovery were utilized in a k-means clustering analysis to categorize respective cities into four different resilience groups. As a supplemental analysis to the modified RIM method, historical data representing the exposure and damage parameters from the 1896, 1933, and 2011 Tōhoku tsunamis were utilized to establish limit states (LSs) for fragility curves to demonstrate the level of response for a specific damage condition. Three limit states were selected for 2%, 20%, and 40% of dwellings in a city being destroyed for a given tsunami event. An ordinal logistic regression was performed to determine whether there was a relationship between the resilience group of each city and the maximum countermeasure height. No statistically significant correlation was found between the maximum height of a coastal hazard countermeasure and the resilience group of each city, which indicates that investing in such infrastructure does not necessarily impact overall community resilience for an extreme event such as the 2011 Tōhoku tsunami. For this scenario, the probability of damage was assessed by developing fragility curves that demonstrated larger probability of exceedance discrepancies between LSs at lower maximum tsunami runup values. Coastal hazard countermeasures therefore may still be effective in limiting damage and thereby improve community resilience for less extreme tsunami events. The results of this investigation will assist government officials and engineers in selecting coastal resilience policies and strategies to limit future impacts from coastal hazards.

Landslide Induced Tsunami Hazard at Volcanoes: the Case of Santorini

The destructive tsunami on 22 December 2018 due to the flank collapse of the Anak Krakatau volcano was a bitter reminder of large tsunami risks and of the shortcomings of the existing tsunami warning systems for atypical sources (tsunamis generated by non-seismic and complex sources). In the Mediterranean, several tsunamis were generated by landslides associated with volcanic systems in the past.The volcanic unrest experienced in 2011–2012 on the Santorini volcanic island in the Southern Aegean Sea pointed out the need to identify and quantify tsunami hazard and risk due to possible flank instability which may be triggered as a result of volcanic unrest or nearby seismotectonic activities. Inspired from this need, in this study we examined three possible landslide scenarios in Santorini Island with tsunamigenic potential. The results show that the scenarios considered in our study are able to generate significant local tsunamis impacting Santorini and the nearby islands, as well as producing significant impact along the coasts of the Southern Aegean Sea. While maximum tsunami amplitudes/arrival time ranges are 1.2 m/30-90 min for locations in the Greek-Turkish coasts in the far field, they are in the order of ≈60 m/1-2 min for some locations at the Santorini Island. The extreme tsunami amplitudes and short arrival times for locations inside the Santorini Island is a major challenge in terms of tsunami hazard warning and mitigation. As an effort to address this challenge, a discussion on the requirements for local tsunami warning system addressing atypical sources in the context of multi-hazard disaster risk reduction is also provided.

Analysis of the Extreme Tsunami Risk to Sanya New Airport in the South China Sea

The Manila trench in the South China Sea (SCS) is identified as being most susceptible to the future major earthquakes. Once a submarine earthquake occurs, the coastal areas and ocean engineering projects around SCS will be affected. Based on the Sanya new airport project, this paper presents an analysis of tsunami impacts to the project region. A series of numerical simulations of tsunami are carried out and compared under different magnitudes of earthquakes. An extreme tsunami induced by a giant earthquake of M9.3 is simulated and analyzed in detail. The tsunami propagation scenarios and surface elevation in the region are presented. The inundation map and flow velocity distribution are analyzed. The impacts of this human project to the coasts are discussed by comparing tsunami wave height with and without the artificial island. According to the numerical results and relevant analysis, the giant tsunami will have great impacts to the artificial island.

Numerical study on the dynamic response of the long-span bridge under potential landslide tsunami

In a tsunami disaster, long-span bridges in coastal areas form critical transport channels for relief so it is crucial that they survive tsunami wave forces. Here we establish a dynamic response analysis framework for long-span bridges and applied it to a landslide tsunami scenario impacting a sea-crossing cable-stayed bridge near Hong Kong, China. First, a meshless numerical approach called Tsunami Squares (TS) simulated the movement of a plausible submarine landslide and its generated near-source waves. Second, we propagated the tsunami ∼300 km to the bridge site and computed wave forces on the bridge substructure. Third, we constructed a dynamic response analysis of the long-span bridge due to those forces. Results show that transverse and longitudinal forces on the bridge substructure reach maximum at different times and transverse load is larger than longitudinal load. The transverse displacement of the cable-stayed bridge dominates both longitudinal and torsional displacements but falls below the safety level even under the most extreme tsunami conditions. Landslide features have non-linear effects on tsunami waves and structural responses so a wide parameter space should be considered. The framework developed here provides effective means for assessing the dynamic state of long-span bridges during tsunami disasters.

Tsunami resonance and standing waves in the South China Sea

This study investigated tsunami resonance and multiscale standing waves induced by a hypothetical extreme tsunami in the South China Sea (SCS). The nonlinear shallow water equation model was adopted to calculate the tsunami propagation from an Mw 9.3 earthquake occurring in the Manila Trench. Then, the sea surface elevation 24 h following the earthquake was computed for spectral analysis to characterize edge and standing waves for the explanation of tsunami oscillations in the semi-enclosed marginal sea. The spectra of background noise at eight tide gauges were calculated and used as a reference. Results showed that standing waves between 29 and 256 min were the dominant wave modes in the entire SCS. The resonance characteristics around Hainan Island and Lingding Bay were also investigated. Spectral analysis at different spatial scales indicated wave trapping and tsunami resonance over the continental shelf and along the coast. The tsunami resonance modes induced by the hypothetical extreme tsunami reveal information regarding energy concentrations and long-lasting tsunamis in the coastal region and provide a novel perspective for identifying at-risk regions in tsunami hazard assessment.

Damming effects of tsunami-borne washed-out trees in reducing local scouring and tsunami energy behind a coastal embankment

During an extreme tsunami event, forests along the shoreline are destroyed and produce numerous pieces of debris that cause further destruction of inland structures. However, if that debris can be properly managed by trapping, it will effectively reduce the flow energy, and doing so will mitigate tsunami-induced damage. Therefore, a series of model scale experiments was performed to elucidate the effects of a debris dam on local scouring and tsunami energy reduction on the landside of a coastal embankment model (EM) on a gravel bed in which the tsunami-borne debris (TBD) was modelled as small actual trees. To further clarify the effects of the realistic modeling approach, the debris was also modelled by circular cylinders for comparison. To demonstrate the effects of debris on damming, the rows of TBD were varied as two (Case 3), four (Case 4), and eight rows (Case 5). Experimental results showed that Case 5 (i.e., eight rows of TBD that were placed from the EM toe) reduced the maximum local scoured depth (i.e., averaged) at the EM toe by about 40.8 – 65.2%, the maximum scoured depth by about 36.3 − 56.5%, and the scoured length by about 34.1 − 41.9%. The trapping capability of the forest decreased significantly when the TBD was modelled as circular cylinders instead of the original trees. The increment in the number of rows of TBD, caused an increased damming effect, which consequently resulted in a shift of the toe of the formed submerged hydraulic jump to the EM top. Therefore, this phenomenon has resulted in a noteworthy reduction in local scouring phenomenon close to the EM toe by reducing the intensity of the overflow hitting the ground directly. A maximum reduction of 43.6 – 48.8% of the total relative energy of the tsunami flow was found when eight rows of TBD were positioned at the beginning of the EM toe.

A mechanics-based method towards risk assessment of RC buildings under tsunami and flow-type hazards

The study presents a simple mechanics-based method to develop analytical fragility functions for the risk assessment of Reinforced Concrete (RC) frame buildings subjected to tsunami or other flow-type hazards (i.e., flood, mud flows, flow-type landslides, etc.). A harmonized framework for the analysis of building portfolios to flow-type hazards is first illustrated. The mechanics-based method for the performance assessment of RC frames with breakaway infill walls subjected to tsunami and flow-type loads, called SAFETI (Structural Assessment to Flows and Extreme Tsunami Inundation), is then presented. For the large-scale risk analysis, a damage levels classification is adopted for both structural and non-structural (i.e., infill walls) components, based on the HAZUS approach. The flow depth is assumed as Intensity Measure. Damage levels computed through SAFETI are validated with ones obtained from a refined finite-element modelling in OpenSees for three case-study RC frames subjected to tsunami. Finally, an application of the SAFETI method is presented to show the feasibility of the mechanics-based procedure to derive analytical fragility curves for a simulated case-study building portfolio subjected to tsunami, flow-type landslides, and flood. The SAFETI method appears a robust solution to perform a consistent fragility assessment at regional scale for tsunami and flow-type hazards, explicitly accounting for the building-to-building variability with limited modelling and computational efforts.

Extreme event probability estimation using PDE-constrained optimization and large deviation theory, with application to tsunamis

We propose and compare methods for the analysis of extreme events in complex systems governed by PDEs that involve random parameters, in situations where we are interested in quantifying the probability that a scalar function of the system's solution is above a threshold. If the threshold is large, this probability is small and its accurate estimation is challenging. To tackle this difficulty, we blend theoretical results from large deviation theory (LDT) with numerical tools from PDE-constrained optimization. Our methods first compute parameters that minimize the LDT-rate function over the set of parameters leading to extreme events, using adjoint methods to compute the gradient of this rate function. The minimizers give information about the mechanism of the extreme events as well as estimates of their probability. We then propose a series of methods to refine these estimates, either via importance sampling or geometric approximation of the extreme event sets. Results are formulated for general parameter distributions and detailed expressions are provided when Gaussian distributions. We give theoretical and numerical arguments showing that the performance of our methods is insensitive to the extremeness of the events we are interested in. We illustrate the application of our approach to quantify the probability of extreme tsunami events on shore. Tsunamis are typically caused by a sudden, unpredictable change of the ocean floor elevation during an earthquake. We model this change as a random process, which takes into account the underlying physics. We use the one-dimensional shallow water equation to model tsunamis numerically. In the context of this example, we present a comparison of our methods for extreme event probability estimation, and find which type of ocean floor elevation change leads to the largest tsunamis on shore.

Effect of Lateral Spacing of Structures on Tsunami-Induced Scour

April Le Quéré, P.; Nistor, I., and Mohammadian, M., 2021. Effect of lateral spacing of structures on tsunami-induced scour. Journal of Coastal Research, 37(4), 813–826. Coconut Creek (Florida), ISSN 0749-0208.Tsunamis are a devastating force, as seen by the extreme tsunamis that struck the Indian and Pacific Oceans over the past two decades: the 2004 Indian Ocean Tsunami, the 2010 Chile Tsunami, and the 2011 Tohoku Japan Tsunami. In those events, flood-induced scouring was found to be an important phenomenon that often led to infrastructure damage. Past research has focused on scouring around single columns and other isolated horizontal structures to attempt to understand the complex processes characterizing this phenomenon. However, given that coastal cities often comprise complex arrangements of multiple structures, often crammed, tsunami inundation flow often finds concentrated paths in between such structures; these flow concentrations increase the resulting scouring. This research is an attempt to inform the scientific community on the potential of augmented scour attributable to flow concentration that is due to the lateral spacing of structures and to compare it with nonconcentrated flow-induced scour. The authors employed the FLOW-3D numerical model for this study. This model was first calibrated using a physical model experiment performed in the dam break flume of the University of Ottawa, Canada. Results from this study demonstrate that flow concentration due to the lateral spacing of structures leads to greater scouring than for the case of an isolated structure and that the magnitude of the scour, for most cases studied, was larger than what is prescribed by the latest building codes.

Green infrastructure for the reduction of coastal disasters: a review of the protective role of coastal forests against tsunami, storm surge, and wind waves

ABSTRACT Green infrastructure, utilizing coastal ecosystems, provides a nature-based solution to counteract coastal hazards and rising sea level. Coastal forests, a major type of green infrastructure, are recognized as natural barriers against ocean waves. They can attenuate waves, mitigate erosion, and stabilize shorelines. With growing interests in coastal forests and their function of adapting to future risks, many researchers studied vegetation effects in coastal protection. Yet our limited expertise in quantifying vegetation-induced resistance limits the practical applications. This paper aims to review and categorize the studies related to wave attenuation and mitigation of sediment erosion by coastal forests and identify the potential directions in future works. We first reviewed field observations of extreme tsunami and weather events which showed the effectiveness of coastal forests in reducing wave energy. Next, we covered the studies on wave–vegetation interaction, including mathematical/numerical models and laboratory tests. We categorized the developed models based on different governing equations and introduced how vegetation effects were incorporated. We also discussed the experiments and vegetation models used in laboratory tests. Besides, we highlighted recent studies on the mitigation of coastal erosion. Finally, we recommend the potential directions to quantify the effects of coastal forests on wave attenuation and sedimentation.

A Source Clustering Approach for Efficient Inundation Modeling and Regional Scale Probabilistic Tsunami Hazard Assessment

For coastal regions on the margin of a subduction zone, near-field megathrust earthquakes are the source of the most extreme tsunami hazards, and are important to handle properly as one aspect of any Probabilistic Tsunami Hazard Assessment (PTHA). Typically, great variability in inundation depth at any point is possible due to the extreme variation in extent and pattern of slip over the fault surface. In this context, we present an approach to estimating inundation depth probabilities (in the form of hazard curves at a set of coastal locations) that consists of two components. The first component uses a Karhunen-Loeve expansion to express the probability density function (PDF) for all possible events, with PDF parameters that are geophysically reasonable for the Cascadia Subduction Zone (CSZ). It is then easy and computationally cheap to generate a large $N$ number of samples from this PDF; doing so and performing a full tsunami inundation simulation for each provides a brute force approach to estimating probabilities of inundation. However, to obtain reasonable results, particularly for extreme flooding due to rare events, $N$ would have to be so large as to make the tsunami simulations prohibitively expensive. The second component tackles this difficulty by using importance sampling techniques to adequately sample the tails of the distribution and properly re-weight the probability assigned to the resulting realizations, and by grouping the realizations into a small number of clusters that we believe will give similar inundation patterns in the region of interest. In this approach, only one fine-grid tsunami simulation need be computed from a representative member of each cluster. We discuss clustering based on proxy quantities that are cheap to compute over a large number of realizations, but that can identify a smaller number of clusters of realizations that will have similar inundation depths. The fine-grid simulations for each cluster representative can also be used to develop an improved strategy, in which these are combined with cheaper coarse-grid simulations of other members of the cluster. We illustrate the methodology by considering two coastal locations: Crescent City, CA and Westport, WA.

Hardware Acceleration of Tsunami Wave Propagation Modeling in the Southern Part of Japan

In order to speed up the calculation of tsunami wave propagation, the field-programmable gate array (FPGA) microchip is used. This makes it possible to achieve valuable performance gain with a modern regular personal computer. The two half-step MacCormack scheme was used herein for numerical approximation of the shallow water system. We studied the distribution of tsunami wave maximal heights along the coast of the southern part of Japan. In particular, the dependence of wave maximal heights on the particular tsunami source location was investigated. Synthetic 100 × 200 km sources have realistic parameters corresponding to this region. As observed numerically, only selected parts of the entire coast line are subject to dangerous tsunami wave amplitudes. The particular locations of such areas strongly depend on the location of the tsunami source. However, the extreme tsunami heights in some of those areas can be attributed to local bathymetry. The proposed hardware acceleration to compute tsunami wave propagation can be used for rapid (say, in a few minutes) tsunami wave danger evaluation for a particular village or industrial unit on the coast.

Field Survey and Numerical Modelling of the December 22, 2018 Anak Krakatau Tsunami

On December 22, 2018, the eruption and flank collapse of the Anak Krakatau volcano generated a tsunami in the Sunda Strait causing catastrophic damage to uninhabited coastlines proximal to the source. Along the heavily populated shores of Banten and Lampung provinces in Java and Sumatra, tsunami waves caused severe damage, extensive inundation and more than 430 deaths. An international tsunami survey team (ITST) deployed 6 weeks after the event documented the tsunami effects including runup heights, flow depths and inundation distances, as well as sediment deposition patterns and impacts on infrastructure and the natural environment. The team also interviewed numerous eyewitnesses and educated residents about tsunami hazards. This ITST was the first to visit and document the extreme tsunami effects on the small islands in the Sunda Strait closest to Anak Krakatau (Rakata, Panjang, Sertung, Sebesi and Panaitan). Along the steep slopes of Rakata and Sertung islands, located less than 5 km from and facing directly towards the southwest flank of Anak Krakatau, all of the dense coastal vegetation was stripped to bare earth up to elevations of more than 80 m, while on the northeast tip of Sertung Island, facing away from the source, a single tree remained standing after flow depths of > 11 m above ground struck there. The runup distributions on the islands encircling Anak Krakatau highlight the directivity of the tsunami source suggesting that the collapse occurred towards the southwest. This manifested as tsunami runup of 10 m that stripped away coastal forests to bare rock for up to 400 m inland in the Ujung Kulon National Park, located 50 km to the south-southwest. Inundation and damage were mostly limited to within 400 m of the shoreline, likely the result of the relatively short wavelengths caused by the landslide generated tsunami. A significant variation in tsunami impact was observed along the shorelines of the Sunda Strait, with runup heights rapidly decreasing with distance from the inferred tsunami source. To model the event we applied a hot-start initial condition that roughly reproduced the measured tsunami runup heights along Rakata and Sertung. The waveforms were then propagated through the Sunda Straight using a Boussinesq-type wave model. The results showed a good fit to the observed heights along the Java and Sumatra coastlines, the northern coast of Panaitan Island and Ujung Kulon Nation Park. The model also produced an acceptable fit to the observed amplitudes at tide gauges. Despite the regional volcanic and tsunamigenic history of the region, and 6-months of eruptive activity prior to the event, the tsunami largely caught the local population off guard. This further highlights the need for community-based education and awareness programs as essential to save lives in locales at risk from locally generated tsunamis.

Paleotsunami record of the past 4300 years in the complex coastal lake system of Lake Cucao, Chiloé Island, south central Chile

In 1960 CE, Lake Cucao on Chiloé Island in south central Chile was inundated by the tsunami of the Great Chilean Earthquake (Mw 9.5). The area of what is now the lake basin has been submerged since the end of the rapid postglacial sea-level rise and has recorded tsunami inundations in its sediment record since then. This study reconstructs the tsunami history of Lake Cucao. Reflection-seismic profiles and side scan sonar data of the lake reveal a tidal delta with a crosscutting channel, which controls the sedimentary environment in the coast-facing part of Lake Cucao. The convergent pattern of seismic reflections near this channel indicates that tidal currents were active in the lake at least episodically since the formation of a major unconformity with strong reflection amplitude, which records the onset of lacustrine sedimentation. A radiocarbon date at the base of one of the 21 collected sediment cores dates this reflector to ~3800 years BP. Little net vertical displacement (≤2 m) in combination with an outlet river channel that can act as a pathway for sediment transport appears to have maintained the sensitivity of Lake Cucao to record tsunami inundation. The sedimentary record contains 15 clastic layers which are interpreted as tsunami deposits. The confidence level on the tsunami interpretation depends on five site-specific criteria, which are: (i) high magnetic susceptibility of the sediment indicating high clastic content, (ii) cross core correlation indicating widespread deposition, (iii) acoustic reflector correlation to the sedimentary record (also indicating widespread deposition), (iv) presence of mud clasts, and (v) age correlation to known paleotsunamis in the area. In this way, eight clastic layers are interpreted as tsunami deposits with a high confidence level, five with a medium confidence level and two with a relatively low confidence level. This study adds a long paleotsunami record on a coastline where extreme tsunamis occur frequently and where long (>2000 years) paleotsunami records are still sparse.

The December 2018 Anak Krakatau Volcano Tsunami as Inferred from Post-Tsunami Field Surveys and Spectral Analysis

We present analysis of the December 2018 Anak Krakatau tsunami in Sunda Strait, Indonesia, from a combination of post-tsunami field surveys, bathymetric changes and spectral analysis of the tsunami tide gauge records. Post-tsunami surveys revealed moderate tsunami height along the coast of Sumatra and Java with maximum surveyed runup of 13.5 m and maximum inundation distance of 330 m. At small islands located close to the volcano, extreme tsunami impacts were observed indicating not only a huge tsunami was generated by large amounts of collapse material which caused notable changes of seafloor bathymetry, but also indicates the role of those small islands in reducing tsunami height that propagated to the mainland of Indonesia. Our spectral analysis of tide gauge records showed that the tsunami’s dominant period was 6.6–7.4 min, indicating the short-period nature of the 2018 Sunda Strait tsunami.

Numerical Study on the Hydrodynamic Characteristics of Submarine Pipelines under the Impact of Real-World Tsunami-Like Waves

Submarine pipelines have been extensively used for marine oil and gas extraction due to their high efficiency, safety, and low price. However, submarine pipelines are vulnerable to extreme waves (i.e., tsunami waves). Previous research has often used solitary waves as a basis for studying the impacts of tsunami waves on submarine pipelines, although the hydrodynamic characteristics and wave properties drastically differ from those of real-world tsunami waves. This paper numerically investigates the hydrodynamic characteristics of tsunami waves interacting with submarine pipelines, but instead uses an improved wave model to generate a tsunami-like wave that more closely resembles those encountered in the real-world. The tsunami-like wave generated based on a real-world tsunami wave profile recorded during a 2011 tsunami in Japan has been applied. Given the same wave height, simulation results show that peak hydrodynamic forces of the tsunami-like wave are greater than those of the solitary wave. Meanwhile, the duration of the acting force under the tsunami-like wave is much longer than that of the solitary wave. These findings underline the basic reasons for the destructive power of tsunamis. It is also noted that the hydrodynamic forces of the pipeline under the tsunami-like wave increase with wave height, but will decrease as water depth increases. In addition to the single pipeline, the complicated hydrodynamic characteristics of pipelines in tandem arrangement have been also numerically studied. It is believed that the findings drawn from this paper can enhance our understanding of the induced forces on submarine pipelines under extreme tsunami waves.

Vulnerability Characteristics of Tsunamis in Indonesia: Analysis of the Global Centre for Disaster Statistics Database

Regional disaster data are important for understanding the characteristics of disasters and for identifying potential mitigation measures. However, many countries have no official disaster database that includes information such as numbers of deaths or damaged buildings for each disaster event. The Global Centre for Disaster Statistics (GCDS) was established to assist countries and organizations in the collection of disaster data. At present, a significant amount of tsunami disaster data are available from Indonesia, which will be used to demonstrate its application for analyzing vulnerability characteristics of historical tsunamis. There are 53 data points covering 13 tsunami events between the year 1861 and 2014. Based on data availability, five tsunami events, namely the 1977 Sumba, the 2004 Indian Ocean, the 2006 Java, the 2010 Mentawai, and the 2011 Great East Japan, were selected. Numbers of deaths and damaged buildings were used in combination with hazard data to estimate vulnerability, defined as the ratio between maximum flow depth against death and building damage ratios. Numbers of evacuees were initially used to estimate actual numbers of exposed population but it was later discovered that this parameter overestimated the exposed population in certain cases. As a result, this study presents the vulnerability characteristics of people and buildings in Indonesia, exposed to unusual or extreme tsunamis, mostly in a condition without or with limited access to official warnings. In brief, a maximum flow depth of 5 m caused an approximate 100% death ratio in the majority of Indonesian tsunamis in this study. On the other hand, death ratio in the 2011 Japan tsunami was limited to 10% because of the early warning and high disaster awareness. Effective disaster risk reduction activities such as official warnings, evacuations, and tsunami education were observed for certain locations. Lastly, adding hazard and population data at the village level is recommended for improving the collection of future tsunami disaster data for the GCDS database.

Quantitative Tsunami Risk Assessment in Terms of Building Replacement Cost Based on Tsunami Modelling and GIS Methods: The Case of Crete Isl., Hellenic Arc

Tsunami risk assessment is an important component of the planning for risk reduction. We considered tsunami risk as a convolution of tsunami hazard, vulnerability of the assets at risk (e.g. buildings) and the economic value exposed. For testing the model, a coastal segment at the west of Heraklion, capital city of Crete Isl., Greece, was selected. Heraklion was hit in the past by strong tectonic and volcanic tsunamis, generated along the Hellenic Arc in the Mediterranean region. The Minoan tsunami produced by pyroclastic flows during the LBA (17th century BC) great eruption of Thera (Santorini) was selected as an extreme tsunami scenario for the hazard (inundation) zone determination through numerical simulation based on Boussinesq equations for fully non-linear waves. It was found that the wave penetrates inland up to ~ 1.2 km, while the maximum water depth is ~ 14 m. The building stock was obtained from the 2011 national census data and validated with the use of orthophotomaps, field inspection and Google Maps. Building vulnerability was determined with the use of the empirical GIS tool DAMASCHE which is based on 2004 Indian Ocean tsunami building damage data and produces damage level by combining water depth and building construction types. The damage level was translated to absolute monetary loss on the basis of cost flat rates determined officially for building replacement, i.e., either reparation or reconstruction, after the destructive earthquakes in Greece during 2014. The method is applicable in other parts of the Mediterranean and beyond provided that appropriate data are available.