The resilience and performance of quay walls during devastating events such as tsunamis and earthquake are critical for coastal infrastructure. Conventional design standards mostly address vertical or inclined quay walls, neglecting the potential benefits of more complex geometry, such as bilinear backface. This study presents a seismic design and stability analysis of quay walls with a bilinear backface under the combined action of tsunamis and earthquake. The study findings reveal a significant reduction in safety factors in terms of sliding and overturning when quay walls are simultaneously exposed to tsunami and earthquake forces. The study also proposes a bilinear wall geometry, considering key factors such as tsunami wave height, water depth, submergence height, excess pore pressure ratio, and wall inclination. This study aims to enhance the design and construction of quay walls with a bilinear backface, thereby improving the safety of coastal structures and communities against these rare but devastating events.

On 1 January, 2024, a moment-magnitude 7.6 earthquake hit Ishikawa Prefecture, located on the main island of Japan facing the Japan Sea. Tsunami followed the strong shaking, and the maximum inundation height was 5.1 m in Shika Town. Strong shaking in Wajima City resulted in widespread damage to buildings and a fire that burnt the Wajima Morning Market. As of 16 February, 241 casualties had been reported, and 42% of them were due to building collapses. In response to all the described damage, a joint field investigation was conducted by Japan and New Zealand. This paper provides an outline of the earthquake and the damage observed in the affected area.

The 2018 Sulawesi Earthquake and Tsunami serves as a backdrop for this work, which employs simple and straightforward remote sensing techniques to determine the extent of the destruction and indirectly evaluate the region's vulnerability to such catastrophic events. Documenting damage from tsunamis is only meaningful shortly after the disaster has occurred because governmental agencies clean up debris and start the recovery process within a few hours after the destruction has occurred, deeming impact estimates unreliable. Sentinel-2 and Maxar WorldView-3 satellite images were used to calculate well-known environmental indices to delineate the tsunami-affected areas in Palu, Indonesia. The use of NDVI, NDSI, and NDWI indices has allowed for a quantifiable measure of the changes in vegetation, soil moisture, and water bodies, providing a clear demarcation of the tsunami's impact on land cover. The final tsunami inundation map indicates that the areas most affected by the tsunami are found in the urban center, low-lying regions, and along the coast. This work charts the aftermath of one of Indonesia's recent tsunamis but may also lay the groundwork for an easy, handy, and low-cost approach to quickly identify tsunami-affected zones. While previous studies have used high-resolution remote sensing methods such as LiDAR or SAR, our study emphasizes accessibility and simplicity, making it more feasible for resource-constrained regions or rapid disaster response. The scientific novelty lies in the integration of widely used environmental indices (dNDVI, dNDWI, and dNDSI) with threshold-based Decision Tree classification to delineate tsunami-affected areas. Unlike many studies that rely on advanced or proprietary tools, we demonstrate that comparable results can be achieved with cost-effective open-source data and straightforward methodologies. Additionally, we address the challenge of differentiating tsunami impacts from other phenomena (et, liquefaction) through index-based thresholds and propose a framework that is adaptable to other vulnerable coastal regions.

On March 11, 2011, the Great East Japan Earthquake triggered tsunamis that reached extensive areas along Japan's Pacific coast. There have been instances where embankments built on plains for expressways mitigated the impact of tsunami damage. In the vicinity of the Sendai-tobu highway, the presence of an embankment approximately 10 m high altered the course of the advancing tsunami, thereby preventing flooding. Establishing a multiplied defense system using road embankments necessitates understanding the deformation and collapse mechanisms of road embankments impacted by tsunamis following seismic motion. In this study, overtopping experiments were conducted by first applying seismic motion to model embankments, followed by introducing the first wave of breaking bores, and then simulating prolonged overtopping by the tsunami. The experimental findings indicated that within the embankments impacted by the tsunami, there was an immediate increase in what is presumed to be pore air pressure following the arrival of the breaking bores, followed by a rise in pore water pressure during subsequent overtopping. Moreover, embankments subjected to seismic motion exhibited accelerated erosion following the overtopping. These results imply that when embankments settle due to an earthquake, leading to relatively higher anticipated inundation depths and the potential for overtopping, it is crucial to implement measures to prevent the settlement of the crest for embankments expected to serve as part of a multiplied defense system.

Development of coastal areas in Japan for various land uses since the 1960s has contributed to industrial upgrades and improved the efficiency of transportation networks. However, there are concerns about the vulnerability of developments on alluvial plains and reclaimed lands to geological events, like ground subsidence due to liquefaction during large earthquakes. Realistic assessment of earthquake and tsunami hazards and evaluation of possible countermeasures require accurate estimation of the amount of subsidence that can be expected from liquefaction at coastal and riverside sites supporting various structures. In this study, to evaluate the amount a river embankment structure might be expected to settle as a result of strong motion from an assumed Nankai Trough great earthquake, we conducted a numerical simulation using the soil-water coupled finite deformation analysis code GEOASIA. We then investigated the effect of the estimated embankment subsidence on tsunami inundation, which was simulated by using nonlinear shallow-water equations and a grid spacing as fine as 3.3 m. The influence of urban structures on the inundated area was taken into account by using a structure-embedded elevation model (SEM). The results showed that subsidence of river embankments and the collapse of parapet walls on top of them would increase both the depth and area of inundation caused by a tsunami triggered by a Nankai Trough scenario earthquake. Our findings underscore the importance of evaluating not only earthquake resistance but also vulnerability of coastal and riverside structures to strong motion in tsunami hazard analyses. Furthermore, the importance of tsunami inundation analysis using a SEM for predicting the behavior of tsunami flotsam in urban areas was demonstrated.

This study explores how Pacitan Bay, Indonesia's coastal vegetation, can help mitigate tsunamis. It combines numerical modelling and field observations to assess the role and performance of vegetation while addressing the existing vegetated occupancy and gap between sectors. The study utilises simulations and on-site data to evaluate how coastal vegetation reduces tsunami wave energy and enhances coastal resilience. The findings emphasise the importance of vegetation as a natural defence against tsunamis in Pacitan Bay and highlight the need to address the open gap. This research offers valuable insights for coastal management, improving future strategies for effective tsunami mitigation.Research highlightsThe research confirms the effectiveness of using a nested grid pattern to accurately simulate tsunamis in intricate coastal areas, showcasing successful grid transitions and propagation of reflected waves.The role of coastal vegetation in reducing the impact of tsunamis is vital, as larger forested areas and denser vegetation result in more effective wave reduction.Challenges faced by coastal vegetation in Pacitan Bay encompass soil quality, microclimate conditions, land-use changes, and threats such as illegal logging and natural events.Addressing these challenges requires a combination of policies, enforcement, community-based initiatives, and collaboration to enhance coastal resilience and maintain a thriving ecosystem.

The 2011 off the Pacific coast of Tohoku Earthquake occurred, and coastal forests were severely damaged by a huge tsunami. Since the disaster, coastal forest restoration projects have been underway by the Forestry Agency and local governments. Detailed time-series monitoring of the regeneration process of coastal forests is important in order to proceed with regeneration appropriately. The Normalized Difference Vegetation Index (NDVI), which uses near-infrared and visible red images obtained from optical satellite observations, has been widely used to survey trees and vegetation. However, it has been reported that NDVI tends to be saturated depending on the observation period and vegetation type. In addition, there is a tendency for index values to be overestimated on the soil surface. In particular, in the case of coastal forest regeneration, the influence of the soil surface is even greater because the complex mixture of soil surface and afforestation is assessed from observation images. To date, many improvement vegetation indices have been proposed to reduce soil surface effects and more appropriately evaluate vegetation activity. However, the applicability of improvement indexes using higher-resolution satellite images for evaluating the regeneration of tsunami-affected coastal forests has not yet been sufficiently investigated.