Preface

The Geomatics International Conference (GeoICON) is an annual scientific meeting organized by the Department of Geomatics Engineering, Institut Teknologi Sepuluh Nopember Surabaya, Indonesia since 2016. Due to the outbreak of Covid-19, the 6th GeoICON 2021 was held virtually on July 27st 2021. The conference had a theme of “Geospatial Technology for Mapping the Future: Solutions for Hazard and Disaster Mitigation. The 6th GeoICON 2021 aims to bring together researchers, scientists, and scholar students to exchange and share their experiences, new ideas, and research results about all aspects of geospatial science and technology. The discussion about the practical challenges encountered is performed and the solutions are adopted. During the conference, speakers of the event comes from many backgrounds such as government, industry, and academics. The participants presented their findings in eight main conference topic tracks, i.e. (A) flood modeling, (B) earthquake, (C) extreme weather and climate change, (D) tsunami simulation, (E) landslide and mass movement, (F) capacity strengthening, (G) sea-level rise, (H) temporal shelter model, as well as discussing potential joint research and collaborations among them. We would like to thank the committees for their strong commitment to organizing this event and the participants who have contributed to this volume. We would also like to thank the editor for their time and valuable remarks as well as the reviewers for their suggestions on how to improve the paper. Our gratitude is also expressed to the publisher for the generous help in publishing this proceeding volume. Lastly, we would like to acknowledge all the contributing sponsors for their generous support of the conference. October 28th, 2021 Dr. Eko Yuli Handoko ST., MT. The 6th GeoICON 2021 Chairman

Insights on the Small Tsunami from 28 January 2020 Caribbean Sea MW7.7 Earthquake by Numerical Simulation and Spectral Analysis

A huge left-lateral strike-slip Mw7.7 earthquake struck the Caribbean Sea on January 28, 2020. Thus, a small tsunami was generated as as result of the earthquake. The information and observational data gathered for the earthquake and tsunami, as well as integrating the regional tectonic setting, were used to describe the seismogenic source’s properties. The COMCOT model was used for tsunami simulation, with Okada’s dislocation model from finite fault solutions for MW7.7 Caribbean Sea earthquake published by the USGS. The simulation results were compare to tide gauge records to validate whether the seafloor vertical displacements generated by strike-slip fault caused a small tsunami. We conduct spectral analysis of tsunami to better understand the characteristics of tsunami records. Tsunami simulation results show that the coseismic vertical displacement caused by a strike-slip MW7.7 earthquake can contribute to the small tsunami, and the anomalously large high-frequency tsunami waves recorded by the George tide gauge in 11 minutes after the earthquake were unrelated to the earthquake-generated tsunami. According to spectrum analysis. The predominant period of the noticeable high frequency tsunami wave recorded by George tide gauge is only 2 minutes. This indicates that the source of small tsunami was close to the George station and travelled a distance of ~ 150 km, indicating a submarine landslide caused by the strike-slip earthquake. The comprehensive analysis shows that the small-scale tsunami was not caused solely by coseismic seafloor deformation from this strike-slip event, but that earthquake-triggered submarine landslide was the primary cause. Hence, the combined effect of two sources leads to the small-scale tsunami.

The Tsunami Simulation Generated by ‘Anak Krakatau’ Volcano Flank Collapse using MIKE 21Hydrodynamics Flexible Mesh with Manning Number Variation

This study aims to calculate the tsunami investment and the estimated arrival time at several locations around the Sunda strait, caused by the December 2018 Krakatao's eruption. The propagation of the tsunami wave is simulated using MIKE 21 Hydrodynamics Flexible Mesh (HD FM). The spatial data consist of the bathymetry and topography of the Sunda Strait area and its surroundings, whilst assumptions are made on the tsunami source topology and its exact location. Several runs of the simulation are then conducted by varying the Manning Number, i.e. bed resistance values, at the tsunami source and throughout the simulation domain, which accordingly would influence the propagation speed, inundation, and arrival time. Smaller Manning's values, which correspond to increasing roughness, are applied at locations closer to the tsunami source. In this simulation, Manning's number ranges from 10 to 40 m1/3s-1. Surface elevation, still water depth, and u and v velocity components are generated from this simulation.

INTERACTIVE AUGMENTED REALITY SIMULATION SYSTEM FOR COASTAL HAZARD EDUCATION

The abstract is based on the project of "extended reality" for effective communication of hazards from extreme coastal events, such as tsunamis and hurricanes. The project attends to use augmented reality (AR) and mixed reality (MR) to allow, for example, a coastal resident to see a digital tsunami crashing onshore and bulldozing through a community, all while standing on their beach or in their driveway. This type of experience provides an emotional impact and long-lasting memory that will guide future planning decisions and proactivity. In this abstract, we focus on applying mobile augmented reality (AR) to a tsunami simulation system and creating this digital extreme event experience. The tsunami modeling studies use the methods and models described in Tavakkol & Lynett (2017), Lynett et al. (2017) and Lynett & Tavakkol (2017).Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/TD4qI5QdAEc

Assessment Of Tsunami Hazard In Sabah – Level Of Threat, Constraints And Future Work

The coastal areas of Sabah are exposed to far-field earthquake-induced tsunamis that could be generated along the trenches of Manila, Negros, Sulu, Cotabato, Sangihe and North Sulawesi. Tsunami simulation models from these trenches indicated that tsunami waves can reach the coast of Sabah between 40 and 120 minutes with tsunami wave heights reaching up to 3 m near the coast. The level of tsunami threat is high in southeast Sabah due to its narrow continental shelf and proximity to tsunami source in the North Sulawesi Trench. The level of tsunami threat is moderate in north and east Sabah due to their proximity to tsunami source in the Sulu Trench. The level of tsunami threat is low in west Sabah due to its distant location to tsunami source from the Manila Trench. While tsunamis cannot be prevented, its impact on human life and property can be reduced through proper assessment of its threat using tsunami simulation models. Unfortunately, constraints remain in producing a reliable tsunami inundation models due to the lack of high-resolution topography and bathymetry data in Sabah and surrounding seas. It would be helpful if such data can be acquired by the relevant government agencies, at least first, in high threat-level areas, such as Tawau and Semporna districts. In order to properly plan mitigation measures tsunami risk mapping should be intensified in high threat-level areas. The locations of settlements (including water villages), population concentrations, types of buildings and houses, road system, drainage system, harbours, jetties and vegetations (including mangroves) need to be mapped in great detail. Based on the detailed tsunami risk map, targeted vulnerable communities could be given continuous and intensive education and awareness on basic tsunami science and tsunami hazard preparedness.

The Effects of Sub-Faults Strike Direction and Landslide Energy on the Propagation of the 2011 Tohoku Earthquake and Tsunami

We carried out a tsunami simulation of the 2011 (Mw 9.0) Tohoku earthquake. We analyze the tsunami run-up modeling by applying additional variables to seismic moment and moment magnitude equation to find out what extent it affects of sub-faults strike direction and landslide energy to tsunami propagation. To investigate the accuracy of run-up and inundation of the tsunami, we processed and analyzed the mainshock and aftershocks by applying scaling law method and inundation equation. We applied the aftershocks data to determine the wide area of the fault. The fault is divided into several sub-faults to make simulation design and scaling formulation adjustment. Each of sub-faults strike direction on simulation design has a different energy one another, which is determined by the strike direction of each fault position. Furthermore, we calculated the affects of submarine landslides on tsunami propagation. To obtain the variable of resultant energy of earthquake and landslide it performed by using the law of mechanical energy conservation. We applied both L-2008 and ComMIT tools for processing tsunami simulation modeling. The result presents that the sub-fault strike direction and landslide energy can increase the propagation energy of the tsunami waves.

Rational Evaluation Methods of Topographical Change and Building Destruction in the Inundation Area by a Huge Tsunami

In the case of huge tsunamis, such as the 2004 Great Indian Ocean Tsunami and 2011 Great East Japan Tsunami, the damage caused by ground scour is serious. Therefore, it is important to improve prediction models for the topographical change of huge tsunamis. For general models that predict topographical change, the flow velocity distribution of a flood region is calculated by a numerical model based on a nonlinear long wave theory, and the distribution of bed-load rates is calculated using this velocity distribution and an equation for evaluating bed-load rates. This bed-load rate equation usually has a coefficient that can be decided using verification simulations. For the purpose, Ribberink’s formula has high reproducibility within an oscillating flow and was chosen by the authors. Ribberink’s formula needs a bed-load transport coefficient that requires sufficient verification simulations, as it consumes plenty of time and money to decide its value. Therefore, the authors generated diagrams that can define the suitable bed-load coefficient simply using the data acquired from hydraulic experiments on a movable bed. Subsequently, for the verification purpose of the model, the authors performed reproduced simulations of topography changes caused by the 2011 Great East Japan Tsunami at some coasts in Northern Japan using suitable coefficients acquired from the generated diagrams. The results of the simulations were in an acceptable range. The authors presented the preliminary generated diagrams of the same methodology but with insubstantial experimental data at the time at the International Society of Offshore and Polar Engineers (ISOPE), (2018 and 2019). However, in this paper, an adequate amount of data was added to the developed diagrams based on many hydraulic experiments to further raise their reliability and their application extent. Furthermore, by reproducing the tsunami simulation on the Sendai Natori coast of Japan, the authors determined that the impact of total bed-load transport was much bigger than that of suspension loads. Besides, the simulation outputs revealed that the mitigation effect of the cemented sand and gravel (CSG) banks and artificial refuge hills reduced tsunami damage on Japan’s Hamamatsu coast. Since a lot of buildings and structures in the inundation area can be destroyed by tsunamis, building destruction design was presented in this paper through an economy and simplified state. Using the proposed tsunami simulation model, we acquired the inundation depth at any specific time and location within the inundated area. Because the inundation breadth due to a huge tsunami can extend kilometers toward the inland area, the evaluation of building destruction is an important measure to consider. Therefore, the authors in this paper presented useful threshold diagrams to evaluate building destruction with an easy and cost-efficient state. The threshold diagrams of “width of a pillar” for buildings or “width of concrete block walls” not breaking to each inundation height were developed using the data of damages due to the 2011 Great East Japan Tsunami.