Study Ofseismic Surge Mechanism Andglacierlake Outburst Risk

There is a high potentiality for moraine-dam collapse due to surgewaves induced by earthquake,since the component materials of moraine-dam are soft and fragile.As moraine-dammed lakes mostly distributed inalpine-strong earthquake region,theobservation data are difficult to obtain,they are obtained far less attentions than artificial dam construction.The magnitude of seismic surge generally does not cause serious threatfor the artificial damconstruction,so the research on the seismic surge wave is relatively small.In the 13th Five-Year Plan,the agenda of the Sichuan Tibet railway through the Southeast Tibet Palongzangbu basinhas been put on,and there is a the most intensive distribution and the largest scaleof monsoon modern marine glaciers in the region,so the risk of glacial lake outburst is high.The seismic surge is an important hazard factor of glacial lake outburst,its influence factors and wave characteristics still need further research and discussion.In this paper,the seismic surge is studied from the following aspects:(1)Based on the investigation of seismic surge and similar surge at home and abroad,the shallow water wave model for simulating seismic surge is obtained by using hydrostatic assumption for Chen Bang-Fuh model.A finite-difference method is used to calculate the SWE.The model is verified against the models of Sato and of Demirel and Aydin with different kinds of seismic waves,peak ground accelerations and water depths.It is also demonstrated that the proposed model is reliable.Finally,an empirical equation for the maximum water elevation of earthquake-induced water waves is developed based on the results obtained using the model.(2)Shaking table experiment in rectangular water tank is carried out to study the water characteristics under earthquake.The influences of seismic waves,peak ground accelerations,water depths and locations on the maximum water elevation were studied.The experiment resultswere analyzed by comparing with the calculation resultsthe numerical model presented in Chapter 2.The prediction formula proposed in Chapter 2 is revised according to the experiment results.The revised empirical formula is in good agreement with the numerical simulation results and the experimental measurement results.(3)In order to study the seismic surge when the reservoir bottom is uneven,shaking table experiment in rectangular water tank is carried outin rectangular water tank at whose bottom are installed wooden sticks to simulate the uneven bottom.The generation,transmission and dissipation of the energy generated by the shaking of the uneven bottom are analyzed.The influences of peak ground accelerations,water depths and bottom uneven heights on the maximum water elevation when the reservoir bottom is uneven were studied.Based on the empirical formula presented in Chapter 3 and the experimental measurement results,an empirical equation for the maximum water elevation of seismic surges which considered the uneven bottom effects is developed.(4)Seismic surges and landslides are bothmajor secondary mountain hazards during anearthquake,and they may occur simultaneously.The earthquake-andlandslide-induced composite surges were investigated through large-scaleshaking table water tank model experiments.Aseries of tests were conducted for various initial waterdepths,peak ground accelerations,slide impactvelocities,and slide volumes.Based on the results ofthe tests,the effects of these parameters on themaximum wave heights of the earthquake-andlandslide-induced composite surges were analyzed.Then,an empirical equation for the maximum wave heightsof the composite surges was developed.(5)Based on the formula of the critical water level for moraine lakeoutbursts presented by Jiang Zhongxin and the calculating methods of seismic surges in different conditions proposed in this paper,the glacial lake outburst risk assessment program under seismic effect is established.Baesd on the Lee Stevan formula,Xie Renzhi formula and Water conservancy Research Institute of the Yellow River Water Conservancy Committeeformula,the outburst flood calculation program isestablished.These programs were used in the case of Midui moraine lake outburst.Considering the water damage situation of line projects caused by the glacial lake outburst in Tibet,the preventive and controlling principle were presented for the main hazards of outburst flood on the line project.