Modelling volcanic tsunamis

Tsunamis generated by volcanic eruptions have caused about 25% of all deaths associated with volcano activity. The 1883 Krakatau eruption is one example of a fairly recent eruption that produced large tsunamis (-35 m) which caused a high death toll. Concern has also been raised by the potential tsunami generation of the Auckland Volcanic Field, and the impact of such events on the Auckland Region. Although the generation of tsunamis by volcanic eruptions is a major hazard, the processes of tsunami generation are poorly understood. A review of volcanic tsunamis identified 10 main mechanisms. Four of these - caldera collapse, debris avalanches, submarine explosions, and pyroclastic flows - have been suggested as the mechanisms producing the largest tsunamis. All four mechanisms have also been suggested as being responsible for the tsunamis produced by the Krakatau eruption. A combination of physical and numerical modelling was used to develop predictive tools to be applied to volcanoes in Indonesia and New Zealand. The physical modelling involved two main investigations: • A 3 dimensional scale model of the Straits of Sunda and Krakatau. This examined the nature of tsunamis produced by caldera collapse, submarine explosions, and water displacement by debris avalanches and pyroclastic flows. • A series of 2 dimensional simulations of the entrance of pyroclastic flows into the sea. A finite element numerical model was applied to the simulation of pyroclastic flow, maar formation and submarine explosion generation of tsunamis within the Auckland Volcanic Field. The physical and numerical model results indicate that large scale pyroclastic flows are probably the cause of the main 1883 Krakatau tsunamis. A tsunami wave can easily be generated by gravity flows entering the water, regardless of the slope. The wave properties depend on the relative densities of the flow and the receiving body, and the velocity of the flow. The angle of entry of the flow into the water determines the deposition pattern of sediment. The formation of the Calmeyers and Steers shallow area on Krakatau event 1883 was reproduced by the pyroclastic experiments using coarse sand and mud with steep entry angle ~ 60°). The more dilute upper component of the pyroclastic flow that traveled along the sea surface for up to 45 km and killed more than 1000 people at Katimbang, Sumatera Island can also be explained. The experiments showed that less dense material from the pyroclastic flow propagates near the water surface. This is even more likely if the material is hot and gas-rich. Physical and numerical model results showed that a single explosion cannot produce a high wave. If a super violent explosion did occur during the Krakatau event, then the water waves (tsunamis) that caused the devastating effect on the surrounding island coastal land were not caused by the direct transfer of explosive forces. Instead a sequence of one or more pyroclastic flows, or collapsing column in and around the Krakatau complex are the most likely mechanism causing the largest tsunami. Numerical modelling of the Auckland Volcanic Field examined 4 scenarios: • A series of submarine explosion; • Pyroclastic flows from Rangitoto Island; • Pyroclastic flows from Browns (Motukorea) Island; • Submarine explosion within the Tamaki Estuary. The first 3 scenarios produced regional effects, while the last was purely local event. It was also found that the efficiency of the submarine explosion mechanism was increased by using a sequence of smaller explosions, instead of one large explosion. However the timing between explosions was found to be critical; if the explosions are too close together or too far apart, the efficiency decreases. It is considered that the optimal timing will vary with water depth and explosive yield. The numerical modelling showed that volcanic tsunamis are not a major threat to Auckland. However under suitable conditions a volcanic eruption could produce moderately large tsunamis that generate strong currents

Study on earthquake and tsunami hazard: evaluating probabilistic seismic hazard function (PSHF) and potential tsunami height simulation in the coastal cities of Sumatra Island

This study uses integrated geological, geodesy, and seismology data to assess the potential tsunami and Probabilistic Seismic Hazard Function (PSHF) near Sumatra’s coastal cities. It focuses on estimating the possible level of ground shaking due to the seismic activity within the Sumatran Fault Zone (SFZ) and subduction zone. It uses the Peak Ground Acceleration (PGA) as a measure. An amplification factor that is based on the previous study is used. It is calculated through the Horizontal-Vertical Spectral Ratio (HVSR), which measures possible surface ground shaking. The Seismic Hazard Function (SHF) is calculated considering magnitudes 6.5 to 9.0 for subduction sources and 6.5 to 7.8 for SFZ sources. Also, the PGA based on the Maximum Possible Earthquake (MPE) magnitude is estimated, and tsunami heights are simulated to assess the possible hazard risk. The tsunami source model in this study is characterized by considering the possibility of the long-term perspectives on giant earthquakes and tsunamis that might occur in subduction zones around the off-coast of southern Sumatra Island. The potentiality source zone is characterized based on the utilization of the cross-correlation of correlation dimension (DC) based on the shallow earthquake catalog of 2010 to 2022 and the SHmax-rate of surface strain rate. Based on the MPE, the relatively high estimated PGA at the base rock was found around Mentawai and Pagai Utara islands at about 0.224 g and 0.328 g, with the largest estimated PGA based on the MPE at the surface with values of about 0.5 g and 0.6 g. The possible maximum tsunami height (Hmax) estimated based on source scenarios position around the west coast of Sumatera Island, such as for Kota Padang and Kota Bungus, reaches up to 12.0 m and 22.0 m, respectively. The findings provide valuable insight into seismic and tsunami hazards, benefiting future mitigation strategies

Hydrodynamic modelling of tsunami inundation in Whitianga

In 2006, Waikato Regional Council (WRC) provided research funding for the Coastal Marine Group, Department of Earth and Ocean Sciences, University of Waikato, to undertake research on the impacts of tsunami inundation on Whitianga town and harbour. The main aims of the study are to: ● Identify potential tsunami sources; ● Establish an understanding of tsunami inundation impacts in Whitianga township and harbour – including the hydrodynamic processes and responses of Mercury Bay, Buffalo Bay, Whitianga Harbour and adjacent land to tsunami wave action; ● Develop tsunami inundation maps, showing depth and velocity (speed) of tsunami waves; and ● Provide sound evidence upon which to base community risk mitigation measures – including recommendations for evacuation planning, public education and awareness, protection of infrastructure, management of impacts to marine vessels and future land use planning. The numerical model used in this study is the 3DD Suite-Computational Marine and Freshwater Laboratory model (Black, 2001). The model has demonstrated the ability to accurately reproduce tsunami hydrodynamics during propagation and run up on both laboratory and real-world scales. There are three primary tsunami sources that could potentially affect Whitianga from the Kermadec Trench, and beyond the New Zealand continental shelf, being: 1. Mt Healy undersea volcano eruptions (15th Century event); 2. Large earthquakes along segments 1 and 2 of the Kermadec Trench subduction zone; and 3. A 1960 Chilean-type earthquake event. Each source is modelled, and the results that show the greatest risk and impacts to Whitianga are used as the basis for the hazard maps and hazard zones. Modelling results indicate that: • The Mt Healy type of eruption produced a minimal impact on Whitianga. The tsunami waves generated from this event did not inundate Whitianga. Despite this, strong currents of up to 2.5 m/s were generated inside Buffalo Bay and at the Whitianga Harbour inlet. •The Kermadec Trench earthquake scenarios with both positive and negative leading waves, as a result of a subduction fault dislocation along segments 1 and 2, have a significant impact on Whitianga. The waves inundate the coastal area up to 2.5 and 3 km inland for the subduction thrust fault and normal fault events respectively, and affect the entire area of Whitianga Harbour. The normal fault event that produces positive leading waves has more impact than the thrust fault event that produces negative leading waves. • The 1960 Chilean-type earthquake event produced tsunami waves that inundated Buffalo Beach Road and houses in Whitianga, as observed by eyewitnesses. Strong currents of up to 5 m/s are generated inside Buffalo Bay and the Whitianga Harbour inlet. The modelling indicates that: • Whitianga would be inundated five times by a Kermadec Trench earthquake scenario, and three times by a 1960 Chilean-type of tsunami • For the Kermadec Trench scenario (normal fault), the first waves penetrate Mercury Bay within 75–98 minutes after the fault rupture • Regardless of the tsunami source, it takes 11–18 minutes for waves to arrive at the Whitianga foreshore once they have entered Mercury Bay. The modelling indicates that the period between waves is 40 – 60 minutes, which is consistent with the 1960 Chilean event. The geometry of Buffalo Bay and Mercury Bay amplify the incoming tsunami waves, and the sea level inside the bay continues to oscillate, even after the sea level outside of Mercury Bay returns to normal. This situation is consistent with eyewitness accounts of the 1960 Chilean tsunami. Modelling also shows that strong currents are produced within Buffalo Bay and Whitianga Harbour, as well as during the overland flows - especially in areas adjacent to the Taputapuatea Stream and in the foreshore area between Albert Street and the wharf. The flow speed ranged from 1.5 m/s to 8 m/s for overland flows, and above 8 m/s within the entrance of Whitianga Harbour and in the middle of Buffalo Bay. For the first time in New Zealand, a combination of non-ground striking and ground striking LIDAR data was used in modelling tsunami inundation, which increased the accuracy of the modelling results considerably. Inundation flow behaviour and the effect of topography, as well as land use, can be analysed more accurately, and a more precise hazard map can be produced accordingly. Mitigation measures suggested to protect the Whitianga waterfront include a combination of enhanced coastal sand dunes and planted forest belts, which could be done along both sides of the Taputapuatea Stream. A stop gate could also be constructed at the entrance of the Taputapuatea Stream to minimise the impact of the tsunami flows upstream. With respect to evacuation, it is concluded that due to the lag time between a local event from the Kermadec Trench and wave arrival at the Whitianga foreshore, there is enough time for residents to be evacuated to shelter sites using major roads. Three locations are identified as evacuation shelter sites. These are the marina parking area and Buffalo Beach scenic reserve (both of which are located on high ground adjacent to the high-risk zone), and further inland at the airfield. Vertical evacuation sites are needed inside the high-risk zone, and recommendations on potential locations are provided. It is important that vertical evacuation measures are integrated into community response plans, and that they be reviewed and revised regularly. Overland flow information derived from modelling using the ground-striking and non-ground striking LIDAR data provides a basis to influence new development that occurs within tsunami hazard risk zones. Overland flow information also indicates the areas of existing development that need protection from future tsunami events. Risk mitigation may be accomplished through redevelopment, retrofit, coastal defence measures, safety planning for ships and boats, land reuse plans, and also via public education and awareness programmes. A major challenge of risk mitigation is to maintain emergency preparedness programmes and procedures when the threat of tsunami is perceived as remote. Periodic exercises are essential to maintain awareness, and regular information should be provided for those occupying tsunami hazard areas. Tsunami are rare events, but their impacts on coastal communities can be devastating. It is quite dangerous to believe that the impacts of a tsunami can be completely prevented by man-made structures (Horikawa and Shuto, 1983). However, possible impacts may be minimised through careful design of solutions based on systematic research. An important consideration for risk mitigation works is that they may affect the quality of daily life, and risk mitigation involves choices and trade-offs between risk management and other uses. Video animations of each scenario are provided at regional, intermediate and local scales. The animations cover tsunami wave behaviour during generation, propagation, run up, and overland flows, and may be used to inform land use planning and public education and awareness programmes

Catastrophic Tsunamis In the Indonesian Archipelago

Tsunamis are not rare events for the Indonesian Archipelago as a consequence of four major plate boundaries that meet and collide, and producing highly active seismic zone that is mostly located under the sea. The ‘tsunami season’ within this region started in 1992 at Hading Bay, Flores Island, with casualties of more than 2000 people, followed almost every two years with the 1994 East Java Tsunami, 1996 Tonggolobibi Sulawesi Tsunami, 1996 Biak Tsunamis, 1998 Papua New Guinea Tsunami, and the Banggai Tsunami in 2000. These represent the tsunami season for the eastern part of the Archipelago, since the western part of Archipelago was mostly quiet until the 26 December 2004 Great Sumatra Earthquake and Tsunami, which occurred at a place that never been thought before on the western-most part of the Archipelago. This earthquake and accompanying tsunamis not only a starting point of tsunami season for the western part of the Indonesian Archipelago, but also as a defining moment for the people who lived in the region in looking at the constellation of the archipelago, that changed the development paradigm into natural hazards based development program. The 26 December 2004 event (Mw > 9.0) is a turning point for the tsunamigenic earthquake studies along the subduction zone. Intensive research of this event provides a new insight into tsunami dynamics and characteristics as reflected by the erosional and deposition patterns of the coastal areas, wave run-up height, flow depth and inundation, wave front and bore formation, wave-structure interactions, coastal protection and management of the low-lying areas, and the importance of consistent education and local knowledge about natural hazards (earthquake and tsunamis). The following event on 28 March 2005 (Mw = 8.5), occurred only 250 km distant from the 26 December 2004 event, and continued further south to Java Island on 17 July 2006 (Mw = 7.6) and 12 September 2007 (Mw = 8.4) on southwest Sumatra Island (Bengkulu) along the Java Trench. Field surveys results, and analysis of the source mechanism and distribution of the resulting tsunami waves along the coast, shows that each near-field tsunami generated within the subduction zone is unique and complex. Scientists have urged the public and policy makers to consider all subduction-type tectonic boundaries to be “locked, loaded and dangerous” zones that possess potential tsunami threats. Reliable and comprehensive databases for past and recent events and subsequent scientific analysis are needed in mitigating the tsunami hazards. Fourteen (14) segments of potential catastrophic tsunamigenic earthquake and 21 volcanogenic tsunami sources were identified based on seismotectonic assessment, historical record, paleotsunami deposits and micro-atoll studies, as well as volcanic type and activities. Most of the volcanogenic tsunamis sources are located in the eastern archipelago around the Banda Arc and the Molluca Sea. Tsunamis from volcanic sources had different characteristic to tsunamis generated by an earthquake mechanism, both in the near field and also far field as revealed by numerical modelling assessment. A numerical modeling of tsunami based on scenarios developed, shows the region is very susceptible to tsunamis with elevation at the shoreline greater than 8 m. With this elevation, there is no structural mitigation that is economically feasible to protect long a coastline based on the assessment of the 26 December 2004 event. The nonstructural mitigation measures such as mangroves and coastal forest or in combination with other soft options such as sand dunes, provides protection to some extent. However, further research needs to be carried out in defining appropriate mitigation measures. These high hazard zones require ‘sacrifice zone’ of at least 1 km from the shoreline, and vertical evacuation is needed to save lives. iii Detailed assessment of tsunami inundation based on the 26 December 2004 event revealed that the distributions of the flow depths are not always inline with distribution of the flow speed. The areas that experienced the deepest flooding does not necessarily experience the fastest flows, while the damage within urban and rural areas mostly coincided with the flow speed distribution rather than runup and inundation depth distribution. Consequently, in assessing the tsunami hazards, especially when making inundation maps, the overland flow speed should be taken into account or incorporated into the inundation map. However, the problem is that not all coastal areas have nearshore bathymetry and topography data at a resolution needed to represent the nearshore and overland flow dynamics. Results from assessment of the tsunami field survey and damage data from recent events provide the necessity information to derive the hazards level that correlate the tsunami elevation at a shoreline with destruction scale inland. This provides enough information to permit the construction of hazard maps for the region where detailed nearshore bathymetry and topography data are not available. The tsunami elevation at the shoreline can be derived from numerical models. As demonstrated during the 26 December 2004 event, the impacts of tsunamis on the coastal areas include not only the destruction of the infrastructure, buildings, housing, coastal landforms as well as a massive casualties, but also the resulting waste and debris that mixes with other flotsam during wave runup and backwash. This may create another huge problem that leads to serious long term adverse environmental consequences. Debris dispersal modelling is applied to the Banda Aceh region based on that event, and shows that understanding the pathway and distribution of the suspended materials and flotsam caused by tsunamis is important for proper hazard mitigation planning and waste management action. In assessing the potential future events, there is uncertainty and some disagreement from results of the tsunamigenic earthquake recurrence interval based on the empirical formula used. These need to be refined with more data such as from continuous Global Position System measurements. Likewise for volcanogenic tsunamis sources, which are better defined by their location but difficult to determine which processes are dominant to generate catastrophic tsunamis for the next events. The rule of thumb of the sea receding as a sign for impending tsunamis from the subduction zone earthquake source is not applicable for most of the volcanogenic tsunamis. For a tsunami generated by volcanic eruption, the warning is the eruption itself, which could be several days before a tsunami event. More research is required to better understand the characteristic of volcanogenic tsunamis. In general, the arrival time of tsunamis along the subduction zone within the Indonesian Archipelago is within 10 – 30 minutes. The best lesson learned is from the people in Simeulue, who recognized a simple messaged, if a significant ground shaking was felt, and the sea recedes; then evacuate to higher ground. This type of community warning and self-evacuation are a challenge for modern life style in the city. Integration of life-long efforts to educate the population about the hazards and preparedness for an extreme event is needed. The most favorable way is to include earthquake and tsunami hazards, and preparedness as part of educational curricula taught at schools

Anak Krakatau volcano emergency tsunami early warning system

On 22 Dec 2018 13:56 UTC a Tsunami was generated from the area of the Anak Krakatau Volcano, with waves propagating in all directions inside the Sunda Strait, the sea portion between the Java and Sumatra islands. The cause of this event seems to have a correlation with the ongoing Volcanic eruption, which was particularly active since June 2018 [4], At the time of the event, the Tsunami Early Warning System currently implemented in Indonesia, could not be used because there was no mechanism to activate the system on the basis of measurement of sea levels or other information from the volcano activities. Given the situation, the Indonesian Authorities have decided to implement an Emergency Early Warning system that can timely inform if any sea level disturbance could represent a Tsunami from the volcano activities and therefore give the possibility to activate the sirens. The Joint Research Centre (JRC), in collaboration with the Indonesian Tsunami Society, the Marine Research Centre of the Ministry of Marine Affairs and Fisheries and the Meteorological, Climatological and Geophysical Agency of Indonesia (BMKG) worked together since the event in December in order to design and implement the new Emergency System. The new system will adopt the real time fast Tsunami instruments (Inexpensive Device for Sea Level Monitoring or IDSL), developed by JRC [ 1], to monitor in real time on a 24/7 the sea level to provide email, SMS alerts, CCTV images and inform about a potential event. The activation of the sirens in the area can be performed after a human verification of the signals. The first 2 devices have been installed at the end of January 2018; other devices will be provided and installed in the near future.JRC.E.1-Disaster Risk Managemen

Serial Ensiklopedia Dinamika PantaiDinamika Pantai Pasca Gempa Bumi Dan Tsunami Sumatera 26 Desember 2004&28 Maret 2005

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Spatial correlation of the maximum shear strain loading rate and the correlation dimension along the Sumatra subduction margin for potential earthquake and tsunami hazard study and analysis

ABSTRACTThe potential earthquake and tsunami hazard along the Sumatra subduction margin, especially around the coast of West Sumatra-Bengkulu, was investigated based on the availability of pre-seismic surface displacement data and shallow crustal earthquake catalogue data from 1907 to 2016. The pre-seismic surface displacement data is based on the displacement data prior to and corrected displacement data after major earthquakes. Using the results of our previous study on the local covariance function and the relationship of Correlation Dimension (DC) with the b-value of Gutenberg-Richter (GR) Law, we estimated the maximum horizontal crustal strain rate (SHmax) and DC around the study area. Least squares prediction based on horizontal displacement data using the local covariance function is used to estimate the displacement model in the entire gridding study area with a 10 km × 10 km size. Furthermore, DC is calculated based on the b-value using the maximum likelihood method based on the input of a constant number of earthquake samples, assuming the regional b-value of GR Law equals 1. Furthermore, the spatial correlation of SHmax and DC can define the area of possible earthquake hazard potential. The identification results are then linked with previous stress reconstruction results for seismic hazard study and analysis. Based on the finding, we then estimate the Seismic Hazard Function (SHF) and Tsunami Height simulation to estimate the possible hazard risk at several observation points. We suggest that the result of this study could be beneficial to understand better the potential seismic and tsunami hazard in the future, mainly to support mitigation purposes

Modelling of Deep Learning-Based Downscaling for Wave Forecasting in Coastal Area

Wave prediction in a coastal area, especially with complex geometry, requires a numerical simulation with a high-resolution grid to capture wave propagation accurately. The resolution of the grid from global wave forecasting systems is usually too coarse to capture wave propagation in the coastal area. This problem is usually resolved by performing dynamic downscaling that simulates the global wave condition into a smaller domain with a high-resolution grid, which requires a high computational cost. This paper proposes a deep learning-based downscaling method for predicting a significant wave height in the coastal area from global wave forecasting data. We obtain high-resolution wave data by performing a continuous wave simulation using the SWAN model via nested simulations. The dataset is then used as the training data for the deep learning model. Here, we use the Long Short-Term Memory (LSTM) and Bidirectional LSTM (BiLSTM) as the deep learning models. We choose two study areas, an open sea with a swell-dominated area and a rather close sea with a wind-wave-dominated area. We validate the results of the downscaling with a wave observation, which shows good results

Debris dispersal modeling for the great Sumatra Tsunamis on Banda Aceh and surrounding waters

The Great Sumatra Tsunami on 26 December 2004 generated large amounts of debris and waste throughout the affected coastal region in the Indian Ocean. In Banda Aceh—Indonesia, the tsunami flows were observed carrying a thick muddy sludge that mixed with all kinds of debris from the destroyed buildings, bridges and culverts, vehicles, fallen trees, and other flotsam. This waste and debris was mostly deposited inland, but traveled both onshore and offshore. Numerical dispersal modeling is carried out to simulate the transport of debris and waste produced by the tsunamis during the event. The model solves the Lagrangian form of the transport/dispersion equations using novel particle tracking techniques. Model results show that understanding the pathway and distribution of the suspended materials and flotsam caused by tsunamis is important for a proper hazards mitigation plan and waste management action, and to minimize serious long-term adverse environmental and natural resources consequences