Study Of Tsunami Hazard Analysis And Tsunami Warning Method Along South China Coast

Manila Trench,located in the east of the South China Sea,is still a seismically active zone,having triggered several tsunamis.As one of the most dangerous potential tsunami source,Manila Trench may trigger catastrophic tsunamis in the future,which threatens the southern coastal area of China.In order to reduce the damages caused by tsunami,the research of tsunami hazard analysis and forecasting methods are especially important.In this paper,multiple nested grid model is applied to COMCOT model to simulate the generation,development and propagation process of a hypothetical tsunami triggered by the earthquake from Manila Trench.First of all,the sensitivity analysis of the linear/nonlinear effect and focal depth were studied.The result indicates that the nonlinear characteristic is significant in shallow water.In order to guarantee the accuracy and stability of the model,it is necessary to set multiple nested grid system in shallow water.Besides,the study of focal depth shows that focal depth plays an important role to the tsunami intensity.That is to say,within a certain depth range,the deeper focal depth is,the greater tsunami hazards will be.But when it exceeds this range,the tsunami hazards become smaller with the increase of focal depth.The focal depth of the worst earthquake scenario is about 33-40 km.Combining historical earthquake records,we set the focal depth as 33 km in this study of tsunami hazard analysis.Five earthquake scenarios along the Manila Trench were simulated.Scenario 2?4 and 5,of which magnitudes are about Mw8.6?Mw 8.8 and Mw 9.0 respectively,may reach level III to IV tsunami risk on the South China coast,causing inundation or serious inundation hazard.Along the North Manila segment,eighteen subfaults had been identified.With the utilization of COMCOT model,tsunami waves generated by each subfault with 1m slip were calculated and the results of two buoys and prediction points were stored as tsunami propagation database.When the tsunami happens,the tsunami waves signal were obtained in buoys in deep ocean earlier than prediction points.Combining tsunami propagation database at buoys,we obtained hypocenter information.Using tsunami propagation database at prediction points,we got tsunami arrival time and tsunami amplitude.Taking the nonlinear factors of the unit subfaults and that between one subfault and other subfaults into consideration,tsunami propagation nonlinear database was built.Based on the nonlinear database,inversion calculation was performed to predict the tsunami wave on prediction points when earthquake happens.The prediction can be completed in 1 min with the prepared database after the buoy signal is obtained,with the numerical errors of predicted tsunami amplitude less than 10% at all selected prediction points.