Multiple cascading hazards triggered by the 2018 Sulawesi, Indonesia, earthquake caused various compounding consequences. A major strike-slip fault movement with along-dip components resulted in intense ground shaking, liquefaction and lateral spreading, large-scale mudflows, and tsunamis. This paper presents observations of such multi-hazard effects on buildings and infrastructure in areas along Palu Bay, based on field reconnaissance work, and discusses the main causes of the disaster by focusing upon the combined effects of the cascading geological hazards. To evaluate the tsunami risk potential of the strike-slip event, tsunami simulations for the 2018 Sulawesi earthquake are performed by considering different model settings for spatial earthquake slip distribution, rake angle, astronomical tidal effect, and co-seismic ground deformation. The numerical results indicate that the co-seismic rupture of a moment magnitude 7.5 strike-slip earthquake, having notable dip components can generate damaging tsunami waves at coastal locations of Palu Bay. The conclusion has important implications for future tsunami hazard assessments in active seismic regions where major fault systems cut across a bay or into the sea.

Settlement of wave-dissipating blocks in front of a caisson is caused by displacement and breakage of blocks directly by wave action and also by sliding of the caisson by wave force. The settlement of blocks, caisson sliding and wave pressure are mutually correlated. The present study has developed a stability analysis method for a composite breakwater with wave-dissipating blocks under the circumstances of climate change effect as seen in sea level rise and increase in storm surges and waves. It is found that the changes of expected caisson sliding distance and necessary caisson width, determined from the allowable excess probabilities for three prescribed sliding distances, against the weight of wave-dissipating block have a tendency to be maximum at certain block weight when repairing of damaged blocks is not done; on the other hand, if repairing is done every time after reaching 5 % damage level of total section, the changes of caisson sliding distance and necessary caisson width against the block weight show monotonous decrease. The effects of climate change on the sliding distance and necessary width are found to make those values larger 10 ~ 60 % than those calculated by constant external forces given from the present climate conditions.

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Super typhoon Haiyan/Yolanda in November 2013 caused coastal flooding and severe damage in coastal zones not only in bays but also along open coastlines. In the Town of Hernani, located on the open Pacific coast of Eastern Samar province in the Philippines, the flooding and resulting washed-away houses were recorded in a widely-viewed video. This paper provides field survey results from Hernani including eyewitness accounts of inundation heights and time series profiles, measured ground levels and estimated sea bottom profiles, and measured dimensions of coastal dikes and of houses shown in the video. Information gathered here suggests that wave groups were the direct cause of coastal flooding in Hernani. Results in this paper will contribute to analysis of large wave disasters and flood prevention in open coastal zones.

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