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To develop disaster mitigation measures in coastal regions affected by earthquakes, it is important to consider the effects of both seismic and tsunami hazards on road structures and assess the social impacts associated with the economic loss and reduction in network functionality. In this paper, a risk- and resilience-based assessment framework is established for road networks under both seismic and tsunami hazards. In the proposed methodology, the risk and resilience are quantified by the economic loss and postdisaster functionality of road networks, respectively. Uncertainties associated with estimations of fault movement, hazard intensity and structural vulnerability are considered when estimating the failure probability using Monte Carlo simulation. Moreover, structural vulnerability against tsunamis is estimated considering the effects of ground motion-induced damage on the reduction in tsunami capacity. As an illustrative example, the road networks in two Japanese cities expected to be affected by the anticipated Nankai Trough earthquake, which would cause strong ground motions and a subsequent tsunami, are analyzed. Finally, the retrofitting prioritization for various structures is discussed based on the risk and resilience quantified as performance indicators for social impacts. [ABSTRACT FROM AUTHOR]

The 2011 Tohoku Tsunami caused severe damage to many coastal defenses along the Japanese coastline, including areas where two adjacent upright sea dikes of different heights met. There are many places along the coastline where structures of different heights and shapes meet due to the various design codes. In this study, the authors aim to examine the tsunami flow around such dikes by conducting three-dimensional hydraulic experiments in a tsunami wave basin and numerical simulations using the fluid dynamics model OpenFOAM. Twelve experimental cases were tested by changing the waveforms, and also by keeping the height of one side of the dike model constant while adjusting the dimensions of the other side. The results show that the difference in height between the structures significantly influences the volume of overtopping over the relatively lower dike and the inundation depth and velocity behind the dikes. Furthermore, different characteristics of inundation patterns are observed between the inundation depth and velocity. Hence, this study illustrates the necessity to re-assess the effectiveness of such structures against tsunami events. [ABSTRACT FROM AUTHOR]

Following the Great East Japan Earthquake, a massive tsunami caused serious damage to coastal dikes. Local scour at the ground behind these dikes reportedly causes dike failures. It is important to reveal the scour process to establish methods for effective scour countermeasures. Herein, we focus on geogrids. To verify this proposal and examine its design, flume-model experiments were performed for non-liquefied and liquefied grounds behind coastal dikes. The results showed that the scour amount and area were reduced drastically when geogrids were present. Geogrids on the sand-bed surface changed the direction of overflow water. Thus, a scour hole developed away from a coastal dike model. Furthermore, geogrids exerted a scour-reduction effect even during liquefaction. [ABSTRACT FROM AUTHOR]

Following the 2011 Tohoku earthquake, coastal forests dissipated the energy of the tsunami and trapped flotsam. Although studies have shown how trees dissipate flow energy and are damaged in the process, the factors determining the trapping of flotsam by lines of trees or their capacity to do so have not been quantitatively examined. Quantitative evaluation of these factors may lead to tree-based strategies for suppressing the secondary damage caused by tsunami flotsam. To increase the ability of trees to mitigate damage, their physical limitations need to be identified. Field surveys revealed that integrated clusters of flotsam were caught by trees even if individual floating objects were smaller than the distance between the trees. Hydraulic experiments revealed relations between physical factors and the capture of flotsam. From these relations, we derived a simple formula for evaluating the trapping capacity of lines of trees. The estimates from our model were consistent with the actual results of the 2011 tsunami in Tagajo city, Miyagi prefecture, where trees did not topple under the forces applied by trapped flotsam. [ABSTRACT FROM AUTHOR]