Abdul Muhari

DAMAGE CHARACTERISTIC AND FIELD SURVEY OF THE 2011 GREAT EAST JAPAN TSUNAMI IN MIYAGI PREFECTURE

On March 11th, 2011, the Pacific coast of Japan was hit by a tsunami generated by the largest earthquake (M9.0) in the history of the country and causing a wide range of devastating damage. Using preliminary reported data from many sources, some topics such as tsunami fatality ratio and tsunami fragility curves for structural damage are discussed and compared with other countries. This paper aims to discuss the damage characteristics of this tsunami as well as its mechanism, as observed through field surveys conducted over the 4 months following the tsunami. The field survey covers 13 areas in the Miyagi prefecture from Kesennuma city in the northernmost region to Yamamoto town in the southernmost region. The arrival time of the first tsunami along the coastal areas in the Miyagi prefecture was confirmed by stopped clocks found during the survey. The damage mechanism of coastal structures such as breakwaters, seawalls, tsunami gates, and evacuation buildings was investigated and discussed. Damage characteristics for each area, i.e., urban areas, port, coastal structures, fisheries, and agricultural areas, were also summarized. The conclusions drawn from the data analysis suggest that experience and education (soft countermeasures) are important to reduce the loss of life, as shown for example in the Sanriku area. The field surveys indicate that wood and reinforced-concrete (RC) structures should be balanced to survive both earthquake and tsunami forces, and the structural design for buildings should be reconsidered after the example in Onagawa town. In addition, coastal structures for tsunami countermeasures (hard countermeasures) should be more properly designed for survival instead of becoming floating debris upon being overturned by a tsunami. The combination of both hard and soft measures is especially necessary for optimizing the outcomes following a great disaster. These recommendations should be taken into consideration in the reconstruction efforts for better tsunami countermeasures in the future.

Rupture process of the 2010 Mw 7.8 Mentawai tsunami earthquake from joint inversion of near-field hr-GPS and teleseismic body wave recordings constrained by tsunami observations

The 25 October 2010 Mentawai tsunami earthquake (Mw 7.8) ruptured the shallow portion of the Sunda megathrust seaward of the Mentawai Islands, offshore of Sumatra, Indonesia, generating a strong tsunami that took 509 lives. The rupture zone was updip of those of the 12 September 2007 Mw 8.5 and 7.9 underthrusting earthquakes. High-rate (1 s sampling) GPS instruments of the Sumatra GPS Array network deployed on the Mentawai Islands and Sumatra mainland recorded time-varying and static ground displacements at epicentral distances from 49 to 322 km. Azimuthally distributed tsunami recordings from two deepwater sensors and two tide gauges that have local high-resolution bathymetric information provide additional constraints on the source process. Finite-fault rupture models, obtained by joint inversion of the high-rate (hr)-GPS time series and numerous teleseismic broadband P and S wave seismograms together with iterative forward modeling of the tsunami recordings, indicate rupture propagation ~50 km up dip and ~100 km northwest along strike from the hypocenter, with a rupture velocity of ~1.8 km/s. Subregions with large slip extend from 7 to 10 km depth ~80 km northwest from the hypocenter with a maximum slip of 8 m and from ~5 km depth to beneath thin horizontal sedimentary layers beyond the prism deformation front for ~100 km along strike, with a localized region having >15 m of slip. The seismic moment is 7.2 × 1020 N m. The rupture model indicates that local heterogeneities in the shallow megathrust can accumulate strain that allows some regions near the toe of accretionary prisms to fail in tsunami earthquakes.

TSUNAMI MITIGATION EFFORTS WITH pTA IN WEST SUMATRA PROVINCE, INDONESIA

This paper describes tsunami disaster mitigation in the West Sumatra region with participatory technology assessment (pTA), which promotes direct interaction among member and experts to discuss issues and reach consensus for mitigation through provision of information and knowledge of science and technology. Two areas were examined: Padang, the capital city; and Painan city, a town in southern West Sumatra Province, Indonesia. Tsunami have damaged these areas at least three times: in 1797, a 5–10-m-high tsunami wave height hit the area; in 1833, a 3–4-m-high tsunami came; and in 2007, an 8.4 Mw earthquake generated a local tsunami with maximum wave height of 1.5 m, as observed near Painan. Because of the high level of tsunami risk resulting from its flat topographic conditions, their respective populations of 820,000 people and 15,000 people are developing tsunami mitigation efforts with support of national institutions and international experts. These cities had different starting points and approaches. Efforts were introduced to produce official tsunami hazards maps. Insights from these lessons and ideas arising from the ongoing process after the 2007 South Sumatra and 2009 Padang earthquakes are discussed herein.

Recent Advances in Agent-Based Tsunami Evacuation Simulations: Case Studies in Indonesia, Thailand, Japan and Peru

As confirmed by the extreme tsunami events over the last decade (the 2004 Indian Ocean, 2010 Chile and 2011 Japan tsunami events), mitigation measures and effective evacuation planning are needed to reduce disaster risks. Modeling tsunami evacuations is an alternative means to analyze evacuation plans and possible scenarios of evacuees’ behaviors. In this paper, practical applications of an agent-based tsunami evacuation model are presented to demonstrate the contributions that agent-based modeling has added to tsunami evacuation simulations and tsunami mitigation efforts. A brief review of previous agent-based evacuation models in the literature is given to highlight recent progress in agent-based methods. Finally, challenges are noted for bridging gaps between geoscience and social science within the agent-based approach for modeling tsunami evacuations.

Validation of linearity assumptions for using tsunami waveforms in joint inversion of kinematic rupture models: Application to the 2010 Mentawai Mw 7.8 tsunami earthquake

Tsunami observations have particular importance for resolving shallow offshore slip in finite-fault rupture model inversions for large subduction zone earthquakes. However, validations of amplitude linearity and choice of subfault discretization of tsunami Greens functions are essential when inverting tsunami waveforms. We explore such validations using four tsunami recordings of the 25 October 2010 Mentawai M_w 7.8 tsunami earthquake, jointly inverted with teleseismic body waves and 1 Hz GPS (high-rate GPS) observations. The tsunami observations include near-field and far-field deep water recordings, as well as coastal and island tide gauge recordings. A nonlinear, dispersive modeling code, NEOWAVE, is used to construct tsunami Greens functions from seafloor excitation for the linear inversions, along with performing full-scale calculations of the tsunami for the inverted models. We explore linearity and finiteness effects with respect to slip magnitude, variable rake determination, and subfault dimensions. The linearity assumption is generally robust for the deep water recordings, and wave dispersion from seafloor excitation is important for accurate description of near-field Greens functions. Breakdown of linearity produces substantial misfits for short-wavelength signals in tide gauge recordings with large wave heights. Including the tsunami observations in joint inversions provides improved resolution of near-trench slip compared with inversions of only seismic and geodetic data. Two rupture models, with fine-grid (15 km) and coarse-grid (30 km) spacing, are inverted for the Mentawai event. Stronger regularization is required for the fine model representation. Both models indicate a shallow concentration of large slip near the trench with peak slip of ~15 m. Fully nonlinear forward modeling of tsunami waveforms confirms the validity of these two models for matching the tsunami recordings along with the other data.

Loss Functions for Small Marine Vessels Based on Survey Data and Numerical Simulation of the 2011 Great East Japan Tsunami

AbstractData for approximately 20,000 small marine vessels damaged by the 2011 Great East Japan tsunami, including information on motor types and tonnage, were collected and used to develop loss functions. The observed maximum tsunami heights from the field survey were used, and the maximum tsunami flow velocities from numerical simulation were obtained. Damage ratios were calculated, and loss functions were fit using linear regression analysis and log-normal distributions. The damage probability was significantly increased when the tsunami height was more than 2 m or when the flow velocity was more than 1 m/s. The results show that small vessels (weighing less than 5 t) with outboard motors were the most vulnerable. In addition, vessels at locations farther from the tsunami source had less damage because they were hit by smaller tsunamis with slower arrival times, which most likely gave them a chance to evacuate to deep sea. The results of this study, including the loss functions, will be useful for macr...

Assessment of tsunami hazards in ports and their impact on marine vessels derived from tsunami models and the observed damage data

This paper presents a detailed study of tsunami hazard in ports and its correlation with the damage suffered by marine vessels. The study aims to develop a new loss function to estimate the potential damage of marine vessels due to tsunami attack based on a novel multivariate statistical modeling method, which used several explanatory variables simultaneously to estimate an outcome or the probability of such outcome. In the first part of the paper, tsunami heights and velocities are numerically modeled by using high-resolution bathymetry and topography data for the southern part of Honshu Island. We apply statistical methods to the complete sequence of spatially distributed time series of tsunami parameters in order to obtain the best fit with the observed damage data. In the second part, we develop loss functions for marine vessels by using ordinal regression, which uses simultaneously several explanatory variables. We perform several statistical tests to determine the appropriate model variables to be used in developing three-dimensional loss estimation surfaces, which provide probability of loss for each combination of measured or simulated values of tsunami parameters. The main feature of the developed loss functions presented in this study is their capability to integrate the key factors influencing the damage probability, such as tsunami parameters, characteristics of marine vessels and the impact of collision experienced by the vessels during the tsunami. Such a robust method, therefore, is crucially important to understand the tsunami impact on ports and, particularly on marine vessels.

A Decade After the 2004 Indian Ocean Tsunami: The Progress in Disaster Preparedness and Future Challenges in Indonesia, Sri Lanka, Thailand and the Maldives

AbstractThe 2004 Indian Ocean tsunami was one of the most devastating tsunamis in world history. The tsunami caused damage to most of the Asian and other countries bordering the Indian Ocean. After a decade, reconstruction has been completed with different levels of tsunami countermeasures in most areas; however, some land use planning using probabilistic tsunami hazard maps and vulnerabilities should be addressed to prepare for future tsunamis. Examples of early-stage reconstruction are herein provided alongside a summary of some of the major tsunamis that have occurred since 2004, revealing the tsunami countermeasures established during the reconstruction period. Our primary objective is to report on and discuss the vulnerabilities found during our field visits to the tsunami-affected countries—namely, Indonesia, Sri Lanka, Thailand and the Maldives. For each country, future challenges based on current tsunami countermeasures, such as land use planning, warning systems, evacuation facilities, disaster education and disaster monuments are explained. The problem of traffic jams during tsunami evacuations, especially in well-known tourist areas, was found to be the most common problem faced by all of the countries. The readiness of tsunami warning systems differed across the countries studied. These systems are generally sufficient on a national level, but local hazards require greater study. Disaster reduction education that would help to maintain high tsunami awareness is well established in most countries. Some geological evidence is well preserved even after a decade. Conversely, the maintenance of monuments to the 2004 tsunami appears to be a serious problem. Finally, the reconstruction progress was evaluated based on the experiences of disaster reconstruction in Japan. All vulnerabilities discussed here should be addressed to create long-term, disaster-resilient communities.

Damage and Reconstruction After the 2004 Indian Ocean Tsunami and the 2011 Tohoku Tsunami

The 2004 Indian Ocean tsunami was one of the world’s worst tsunamis and caused devastating damage in many Asian countries. Then, in 2011, Japan was hit by a tsunami that was generated by the greatest earthquake in the country’s history. This paper discusses the damage caused by these tsunamis and subsequent reconstruction. Introduced first are the experience gained and lessons learned for future tsunami mitigation, such as tsunami awareness, proper evacuation building and the memorial parks created in the countries affected by the 2004 tsunami (Indonesia, Sri Lanka and Thailand). Second, human casualties and building damage are discussed using fatality ratios and fragility curves, respectively. These analyses show that experience and awareness help reduce human casualties in the Sanriku area, and wooden houses damaged by the 2011 tsunami fared better than in previous historical events. The damage by the 2011 tsunami to structures designed to protect against tsunamis is summarized. Most of these structures could not withstand and protect from the tsunami because they were not designed for such a large tsunami as expecting of such great event. Finally, examples of ongoing reconstruction in Japan are introduced. Most reconstruction efforts were planned after considering the lessons learned from the tsunami’s impact, and the towns in question are now strengthening their disaster prevention-related plans to be better prepared for future tsunamis.

Coupled Tsunami Simulations Based on a 2D Shallow-Water Equation-Based Finite Difference Method and 3D Incompressible Smoothed Particle Hydrodynamics

In 2011, the tsunami generated by the Great East Japan Earthquake devastated infrastructure along the Pacific coast of northeastern Japan. In particular, the collapse of bridges resulted in much disruption to traffic, which led to delays in recovery after the disaster. We are developing a multi-scale and multi-physics tsunami disaster simulation tool to evaluate the safety and damage of infrastructure from huge tsunami. Multistage zooming tsunami analysis is one of the possible methods for implementing a high-resolution three-dimensional (3D) tsunami inundation simulation for a city. In this research, a virtual wave source that includes transition layers is proposed for a coupled simulation based on 3D particle simulation. The zooming analysis has been undertaken using the same particle method and a two-dimensional (2D) finite difference simulation. The 3D particle coupled simulation has been examined and validated.