Tsunami Inundation Zone Research Articles

Permodelan Tsunami dan Implikasinya Terhadap Mitigasi Bencana di Kota Palu

Kota Palu Sulawesi Tengah adalah salah satu wilayah di Indonesia yang rentan terhadap bencanatsunami dan perlu memiliki suatu rencana tindakan preventif dan mitigasi untuk mengurangi potensiresiko. Studi ini menganalisa zona genangan tsunami dan implikasinya terkait kegiatan mitigasibencana di Kota Palu. Studi ini menggunakan pendekatan kuantitatif menggunakan Sistem InformasiGeografis (SIG) untuk memetakan wilayah yang rawan bencana tsunami. Studi ini menggunakan costdistance untuk memodelkan bencana tsunami, serta menggunakan spatial analyst dan network analystuntuk menganalisa tingkat bahaya, kerentanan, dan resiko bencana tsunami, serta penentuan ruteevakuasi. Analisis mengindikasikan berikut ini: (1) Kota Palu memiliki potensi yang besar terhadaprendaman tsunami, (2) kawasan bahaya tsunami mencakup 9,63% dari total luas kota, (3) kawasanrentan tsunami 9,83% total luas kota, (4) kawasan resiko tsunami 3,83% total luas kota, dan (5)terdapat 50 shelter sebagai lokasi evakuasi dan 108 rute evakuasi di seluruh kota. Kawasan terbangundi wilayah pesisir Teluk Palu teridentifikasi memiliki tingkat resiko bencana tsunami yang tinggi. Jalurevakuasi yang ada tersebar melalui kawasan terbangun dengan jumlah rute yang berbanding lurusdengan kepadatan pendudukKata kunci: permodelan tsunami, resiko, shelter, rute evakuasi, Kota Palu

Performance of Reinforced Concrete Columns Impacted by Water-Borne Shipping Containers

Numerous buildings have been severely damaged during hurricanes and tsunamis due to impact of water-borne massive objects such as barges, boats, heavy vehicles, and shipping containers. Failure of columns which are the primary load-carrying members of a building due to such impact loads, could significantly affect the performance of a building. This paper reports the results of the numerical investigation of reinforced concrete (RC) columns subjected to impact loads from water-borne shipping containers which have been dislodged during tsunamis. Existing methods to estimate peak impact force on structures due to tsunami water-borne massive objects are reviewed and their limitations are discussed. High-fidelity numerical simulation of the shipping container-column impact is carried out using the nonlinear finite element code LS-DYNA. The container model includes all significant structural elements and associated details. Typical RC columns having square and circular cross-sections are considered to investigate the damage to the container and column, and it is shown that the shape of the column cross-section significantly affects the peak impact force. The effects of container specific parameters such as velocity, height above ground level, and container orientation on peak impact force are studied. A series of RC columns is considered to investigate effects of transverse reinforcement ratio, longitudinal reinforcement ratio, column section size, and axial load ratio on peak impact force; and formulae to estimate the peak impact force on RC columns are obtained. Damage to the column is presented in terms of the damage index characterized by degradation of axial load carrying capacity and results will be useful for improving impact resistance of RC columns in buildings located in tsunami inundation zones.

A 3-tier tsunami vulnerability assessment technique for the north-west coast of Peninsular Malaysia

The 2004 tsunami that struck the Sumatra coast gave a warning sign to Malaysia that it is no longer regarded as safe from a future tsunami attack. Since the event, the Malaysian Government has formulated its plan of action by developing an integrated tsunami vulnerability assessment technique to determine the vulnerability levels of each sector along the 520-km-long coastline of the north-west coast of Peninsular Malaysia. The scope of assessment is focused on the vulnerability of the physical characteristics of the coastal area, and the vulnerability of the built environment in the area that includes building structures and infrastructures. The assessment was conducted in three distinct stages which stretched across from a macro-scale assessment to several local-scale and finally a micro-scale assessment. On a macro-scale assessment, Tsunami Impact Classification Maps were constructed based on the results of the tsunami propagation modelling of the various tsunami source scenarios. At this stage, highly impacted areas were selected for an assessment of the local hazards in the form of local flood maps based on the inundation modelling output. Tsunami heights and flood depths obtained from these maps were then used to produce the Tsunami Physical Vulnerability Index (PVI) maps. These maps recognize sectors within the selected areas that are highly vulnerable to a maximum tsunami run-up and flood event. The final stage is the development of the Structural Vulnerability Index (SVI) maps, which may qualitatively and quantitatively capture the physical and economic resources that are in the tsunami inundation zone during the worst-case scenario event. The results of the assessment in the form of GIS-based Tsunami-prone Vulnerability Index (PVI and SVI) maps are able to differentiate between the various levels of vulnerability, based on the tsunami height and inundation, the various levels of impact severity towards existing building structures, property and land use, and also indicate the resources and human settlements within the study area. Most importantly, the maps could help planners to establish a zoning scheme for potential coastline development based on its sensitivity to tsunami. As a result, some recommendations on evacuation routes and tsunami shelters in the potentially affected areas were also proposed to the Government as a tool for relief agencies to plan for safe evacuation.

Method to determine the locations of tsunami vertical evacuation shelters

The 2004 Indian Ocean tsunami and the 2011 Great Tohoku Japan earthquake and tsunami focused a great deal of the world’s attention on the effect of tsunamis on buildings and infrastructure. When a tsunami impacts structures in a coastal community, the structures are often not strong enough to withstand the forces and may collapse. Therefore, to maximize the survival probability, people evacuate to higher ground or move outside the inundation zone. However, this is not always possible because of short warning times for near-field tsunamis. Thus, sheltering-in-place or “sheltering-near-place” using vertical evacuation should be considered as an alternative approach to lateral evacuation from a tsunami inundation zone. This paper presents the method and results of a study to develop and demonstrate a methodology that applied genetic optimization to determine optimal tsunami shelter locations with the goal of reducing evacuation time, thereby maximizing the probability of survival for the population in a coastal community. The City of Cannon Beach, Oregon, USA, was used as an illustrative example. Several cases were investigated ranging from a single shelter to multiple shelters with locations of high elevation already in place near the city. The method can provide decision-support for the determination of locations for tsunami vertical evacuation shelters. The optimum location of the shelter(s), which was found to vary depending on the number of shelters considered, can reduce the evacuation time significantly, thereby reducing the number of fatalities and increasing the safety of a community.

Mapping of Building Damage of the 2011 Tohoku Earthquake Tsunami in Miyagi Prefecture

The authors visually inspected the building damage caused by the 2011 Tohoku earthquake tsunami, using the pre and post-event aerial photos. First, we prepared the mosaic of post-tsunami aerial photos acquired by Geospatial Information Authority of Japan (GSI), and conducted the visual inspection of buildings damage to classify the damage. The damage classification results are compiled with building shape files on GIS for mapping the structural vulnerability in the tsunami inundation zone. Finally, we discussed the structural vulnerability in the tsunami affected area based on mapping results of building damage.

The post-depositional changes of the onshore 2004 tsunami deposits on the Andaman Sea coast of Thailand

The Indian Ocean tsunami flooded the coastal zone of the Andaman Sea and left tsunami deposits with a thickness of a few millimetres to tens of centimetres over a roughly one-kilometre-wide tsunami inundation zone. The preservation potential and the post-depositional changes of the onshore tsunami deposits in the coastal plain setting, under conditions of a tropical climate with high seasonal rainfall, were assessed by reinvestigating trenches located along 13 shore-perpendicular transects; the trenches were documented shortly after the tsunami and after 1, 2, 3 and 4 years. The tsunami deposits were found preserved after 4 years at only half of the studied sites. In about 30% of the sites, the tsunami deposits were not preserved due to human activity; in a further 20% of the sites, the thin tsunami deposits were eroded or not recognised due to new soil formation. The most significant changes took place during the first rainy season when the relief of the tsunami deposits was levelled; moderate sediment redeposition took place, and fine surface sediments were washed away, which frequently left a residual layer of coarse sand and gravel. The fast recovery of new plant cover stabilised the tsunami deposits and protected them against further remobilisation during the subsequent years. After five rainy seasons, tsunami deposits with a thickness of at least a few centimetres were relatively well preserved; however, their internal structures were often significantly blurred by roots and animal bioturbation. Moreover, soil formation within the deposits caused alterations, and in the case of thin layers, it was not possible to recognise them anymore. Tsunami boulders were only slightly weathered but not moved. Among the various factors influencing the preservation potential, the thickness of the original tsunami deposits is the most important. A comparison between the first post-tsunami survey and the preserved record suggests that tsunamis with a run-up smaller than three metres are not likely to be preserved; for larger tsunamis, only about 50% of their inundation area is likely to be presented by the preserved extent of the tsunami deposits. Any modelling of paleotsunamis from their deposits must take into account post-depositional changes.

A method for estimating casualties due to the tsunami inundation flow

This study develops a method for estimating the number of casualties that may occur while people evacuate from an inundation zone when a tsunami has inundated an area. The method is based on a simple model of hydrodynamic forces as they affect the human body. The method uses a Tsunami casualty index (TCI) computed at each grid point of a numerical tsunami model to determine locations and times within the tsunami inundation zone where evacuation during the tsunami inundation is not possible and therefore where casualties are likely to occur. The locations and times can be combined with information about population density to compute the potential number of casualties. This information is useful in developing tsunami evacuation routes that avoid such locations. To illustrate the method, it is applied to the Seattle waterfront in Washington State, USA, that is under the threat of possible tsunami disasters due to Seattle Fault earthquakes. Preliminary results suggest that the tsunami casualties may occur within the Seattle waterfront for 15 min, during the time interval from 3 to 18 min after a large Seattle Fault tsunami is generated when the background tide level is mean high water.