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Earthquakes occurring in the Ryukyu Trench, Nankai Trough, and Japan Trench can trigger tsunamis, affecting Hangzhou Bay, China. The 2011 Tohoku tsunami reached the east China coast and resulted in prolonged oscillations in Hangzhou Bay. We used this event as an example and studied the resonance behavior in Hangzhou Bay by spectral and modal analyses. We simulated the wavefield of the 2011 Tohoku tsunami and validated the modeling results using the tide gauge records. The spectral analysis based on the fast Fourier transform of the entire bay area indicated that the resonance oscillations with periods of 66 and 54 min had the highest energy amplification, and the mode of 120 min had a large amplitude near Zhenhai and Fengxian. Additionally, we conducted a modal analysis that relied solely on bathymetry data to analyze the eigenmodes of natural oscillations inside the bay. The regional bay-scale oscillations had periods of up to 286 min. The energy amplification area was generally consistent with the spectral analysis. These findings have implications for tsunami hazard assessments in coastal communities.

Tsunami impacts along the coastline of Chinese Mainland received little attention until the 2011 M w 9.0 Tohoku earthquake and tsunami devastated the neighboring country of Japan and produced 30-60 cm wave amplitudes along the East China coasts (Figure 1). In the wake of the Tohoku event, the emergency authorities of China started to ponder how a similar event elsewhere in the Pacific Rim might affect the coastal fringe of China, where the coastal communities built on low land with hundreds of millions of residents and vast infrastructures would be devastated by severe coastal inundation.For a long period of time, the tsunami hazards in Chinese Mainland were not fully addressed due to two main reasons: a vast and shallow Abstract A Probabilistic Tsunami Hazard Assessment (PTHA) study on the Chinese Mainland and the Taiwan Island was conducted. Characterized by broad and shallow continental shelves, the offshore region along Chinese Mainland's east coast yields a significant nonlinear effect and bottom friction to the propagating long waves. To address these shallow-water effects, a fully nonlinear Boussinesq model was used in the computation-based PTHA framework. We found that the inappropriate usage of the linear wave model could considerably overestimate the tsunami hazards along the East China Sea (ECS) and the Yellow Sea. Tsunami hazard along the coastline of Chinese Mainland is generally moderate. Elevated tsunami hazard levels are found along both flanks of the Yangtze and Pearl estuaries. The probability of these coastlines impacted by 1 m or greater tsunami waves (at 10-m isobath) is about 14%-40% in next century. The shallow and tongue-shaped submarine terrain amplifies the hazard level by trapping the tsunami energy in these areas. Major subduction zones in the Northwest Pacific were identified as the main sources of destructive events along the coast of ECS and the Taiwan Island, while the Manila Trench is the main source zone that threatens the Northern South China Sea. The tsunami hazards generated by the crustal earthquakes are modest, yet not negligible, particularly in the Taiwan Strait. We found the risk of tsunami inundation along the coast of Shanghai is low based on the hazard curves of total water level that incorporates the aleatory uncertainty of tides. Plain Language Summary Tsunamis are infrequent yet devastating natural hazards. Most tsunami waves are generated by underwater earthquakes, and propagate onshore with transformation of wave amplitude and wave length. The Probabilistic Tsunami Hazard Assessment is a quantitative means to estimate the probability of tsunamis affecting the coastal areas of interest, with the purposes of enhancing public awareness and assisting disaster-mitigation activities. Our study aims to address the common concerns of whether the subduction zones in the Pacific Ocean and the local crustal faults may endanger China's low-lying coastal areas that are susceptible to tsunami inundation. The main finding of the study is that both flanks of the Yangtze Estuary a...

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