Description: Large tsunamis occur infrequently but have the capacity to cause enormous numbers of casualties, damage to the built environment and critical infrastructure, and economic losses. A sound understanding of tsunami hazard is required to underpin management of these risks, and while tsunami hazard assessments are typically conducted at regional or local scales, globally consistent assessments are required to support international disaster risk reduction efforts, and can serve as a reference for local and regional studies. This study presents a global-scale probabilistic tsunami hazard assessment (PTHA), extending previous global-scale assessments based largely on scenario analysis. Only earthquake sources are considered, as they represent about 80% of the recorded damaging tsunami events. Globally extensive estimates of tsunami run-up height are derived at various exceedance rates, and the associated uncertainties are quantified. Epistemic uncertainties in the exceedance rates of large earthquakes often lead to large uncertainties in tsunami run-up. Deviations between modelled tsunami run-up and event observations are quantified, and found to be larger than suggested in previous studies. Accounting for these deviations in PTHA is important, as it leads to a pronounced increase in predicted tsunami run-up for a given exceedance rate.

Description: Published

Description: 219-244

Description: 6T. Studi di pericolosità sismica e da maremoto

Description: A sensitivity study is undertaken to assess the utility of different onshore digital elevation models (DEMs) for simulating the extent of tsunami inundation using case studies from two locations in Indonesia. We compare airborne IFSAR, ASTER, and SRTM against high resolution LiDAR and stereo-camera data in locations with different coastal morphologies. Tsunami inundation extents modeled with airborne IFSAR DEMs are comparable with those modeled with the higher resolution datasets and are also consistent with historical run-up data, where available. Large vertical errors and poor resolution of the coastline in the ASTER and SRTM elevation datasets cause the modeled inundation extent to be much less compared with the other datasets and observations. Therefore, ASTER and SRTM should not be used to underpin tsunami inundation models. A model mesh resolution of 25 m was sufficient for estimating the inundated area when using elevation data with high vertical accuracy in the case studies presented here. Differences in modeled inundation between digital terrain models (DTM) and digital surface models (DSM) for LiDAR and IFSAR are greater than differences between the two data types. Models using DTM may overestimate inundation while those using DSM may underestimate inundation when a constant Manning's roughness value is used. We recommend using DTM for modeling tsunami inundation extent with further work needed to resolve the scale at which surface roughness should be parameterized.

Description: The ultimate goal of establishing InaTEWS is to reduce as much as possible the victims due to tsunami. Since 2008, InaTEWS has been operated by BMKG and has shown its performance, proven by its ability to reliably detect and analyze earthquakes within 5 minutes, produce early warnings, and disseminate the products promptly. One of the important elements in the tsunami early warning is the availability of a pre-calculated tsunami database. The tsunami database provides the information about estimated tsunami arrival times and heights in the affected area. In InaTEWS, the pre-calculated tsunami database is integrated into a decision support system that helps operators to take decisions in issuing tsunami warnings. In 2012, this system has been equipped with a database of tsunami simulations covering the Sunda Zone. Obviously this coverage is not sufficient to account for the Eastern part of Indonesia that is also prone to tsunami. As a result that stage of the tsunami result needs to be extended. A project involving BMKG, Alfred Wegener Institute (AWI) and DMInnovation started in May 2015 to strengthen the decision support system of InaTEWS. Several workshops at BMKG were carried out to expand the scenario database in eastern Indonesia. The basis for tsunami scenario computations is the unstructured mesh finite-element numerical model TsunAWI developed by AWI. It is based on non-linier shallow water theory. The discretization scheme is based on finite elements with the mesh generation (covering the whole Indonesian region) that allows for an accurate local resolution along the coast while keeping coarse resolution in the deep ocean. The discretization of faults as a source for tsunami model was developed by Geoscience Australia / DMInnovation. The tsunami scenarios have been calculated for 13 additional source zones, on total 11949 scenarios in eastern Indonesia. The data products of all these scenarios are integrated to the decision support system TOAST developed by gempa GmbH via the Scenario Database Interface TsunDaBI. The sensitivity of the scenarios database with respect to the epicenter density and magnitude variation needed to be assessed, to test as to whether the current tsunami database is already sufficient or additional simulations are needed. In total the scenario repository was extended from 4580 to more than 16000 simulations. The extended tsunami database is expected to improve the tsunami warning bulletin in East Indonesia considerably.

Description: Applying probabilistic methods to infrequent but devastating natural events is intrinsically challenging. For tsunami analyses, a suite of geophysical assessments should be in principle evaluated because of the different causes generating tsunamis (earthquakes, landslides, volcanic activity, meteorological events, and asteroid impacts) with varying mean recurrence rates. Probabilistic Tsunami Hazard Analyses (PTHAs) are conducted in different areas of the world at global, regional, and local scales with the aim of understanding tsunami hazard to inform tsunami risk reduction activities. PTHAs enhance knowledge of the potential tsunamigenic threat by estimating the probability of exceeding specific levels of tsunami intensity metrics (e.g., run-up or maximum inundation heights) within a certain period of time (exposure time) at given locations (target sites); these estimates can be summarized in hazard maps or hazard curves. This discussion presents a broad overview of PTHA, including (i) sources and mechanisms of tsunami generation, emphasizing the variety and complexity of the tsunami sources and their generation mechanisms, (ii) developments in modeling the propagation and impact of tsunami waves, and (iii) statistical procedures for tsunami hazard estimates that include the associated epistemic and aleatoric uncertainties. Key elements in understanding the potential tsunami hazard are discussed, in light of the rapid development of PTHA methods during the last decade and the globally distributed applications, including the importance of considering multiple sources, their relative intensities, probabilities of occurrence, and uncertainties in an integrated and consistent probabilistic framework.

Description: Published

Description: 1158–1198

Description: 5T. Modelli di pericolosità sismica e da maremoto

Description: JCR Journal

Description: This study reports on recent developments of the Indonesia Tsunami Early Warning System (InaTEWS), specifically the tsunami modeling components used in the system. It is a dual system: firstly, InaTEWS operates a high-resolution scenario database pre-computed with the finite element model TsunAWI; running in parallel, the system also contains a supra real-time modeling component based on the GPU-parallelized linear long-wave model easyWave, capable of dealing with events outside the database coverage. The evolution of the tsunami scenario database over time is covered in the first sections also touching on the involved capacity building efforts. Starting with a coverage of just the Sunda Arc region, the database now includes scenarios for 15 fault zones. The study is augmented by an investigation of warning products used for early warning; the estimated wave height (EWH) and the estimated time of arrival (ETA). These parameters are determined by easyWave and TsunAWI with model specific approaches. Since the numerical setup of the two models is very different, the extent of variations in warning products is investigated for a number of scenarios, where both pure database scenarios and applications to real events are considered. Finally, the performance of the system in past tsunami events is reviewed to point out major system updates.

Description: Chemical Reviews DOI: 10.1021/cr300108a