Numerical Simulation of Seismic Tsunami Dissemination at the Continental Shelf of the East China Sea
DONG Fei-fei1,WEN Yan-lin2,DENG Hui1,ZHU Yuan-qing2,LI Zheng1(1.Earthquake Administration of Jiangxi Province,Nanchang,Jiangxi 330039,China; 2.Earthquake Administration of Shanghai,Shanghai 200062,China)
The seismogenic tsunami is a type of sea wave directly caused by uplifting and subsiding of the ocean floor.It generally has substantial destructive power and can create severe damages to lives.Tsunami studies are important in the field of disaster prevention,particularly in tsunami discrimination and sea-quake disaster evaluation. Chinese scholars conducted studies in this field mainly after the 2004 Indonesia tsunami.In the South China Sea,the huge possibility of seismic tsunami occurrence has become a significant issue.The coastal area of East China Sea is the most economically developed and densely populated region of the country;a tsunami occurrence in this area would be catastrophic.No numerical simulation for tsunamis has been conducted for the East China Sea;therefore,research on the characteristics of potential tsunamis in this area is crucial for tsunami identification and disaster assessment. Such tsunami research for the East China Sea region is the focus of this paper.The geological background of seismic activity history,spatial-temporal tsunami distribution characteristics,potential source area of Okinawa Trough,and occurrence possibility of earthquakes and tsunamis in the East China Sea formed the basis for discussion,in addition to identification and scope of potential tsunamis. By using numerical simulation methods,we assumed five focal points in the Okinawa Trough,and we set six seismic tsunami experience parameters for 6.0-9.0 magnitude as the initial conditions.We thoroughly examined 30 earthquake examples that could generate tsunamis,analyzed the tsunami dissemination process in the East China Sea,and discussed the possibility of a tsunami disaster in the coastal areas of Shanghai in detail. The results show that at different source points with the same magnitude,the initial tsunami wave height is same;thus,the earthquakes with magnitudes less than 8.0 had a negligible effect on Shanghai.For those with magnitude 8.0,only the source point at the northernmost region of Okinawa Trough had an obviously impact.Almost all of the earthquakes with magnitudes of 8.5 and 9.0 had a significant influence on the coastal areas of Shanghai,with the largest potential wave height reaching 3.9 m. The analysis results were and combined with water level changes recorded by a tsunami instrument to estimate the tsunami disaster occurrence potential.Because tide is a major factor in daily water level changes,we predicted the tide at the monitoring points with the numerical simulation methods.The results strongly correlated with the observation data.We considered the water level changes at the monitoring points caused by the Okinawa Trough magnitude 8.5 earthquake occurring at the northernmost point and the tidal prediction results of the entire day to determine the post-shock theoretical value of the water level at various times. The results show that the East China Sea is highly susceptible to a seismic tsunami,the Okinawa Trough is a potential risk source area for Shanghai,and the influence from northern section of the trough is greater than that from the southern section.