我国地震海啸危险性概率分析方法

Probabilistic seismic hazard analysis (PSHA) has become standard practice in the evaluation and mitigation of seismic hazard. Probabilistic tsunami hazard analysis (PTHA) achieves the same goal for hazards posed by tsunami. Although this field is not very developed yet, this method offers great advantages for evaluating the total risk including the seismic and tsunami to coastal communities, facilities, and infrastructure. Tsunami hazard analysis has been undergone many years in Japan，America and other countries and some methods had been applied in the tsunami mitigation. In China, the tsunami research is just recognized by the public and the definition and method of probabilistic earthquake tsunami hazard analysis have not been proposed yet. We will develop the China PTHA method and the probabilistic tsunami inundation maps for China based on this delineated tsunami sources. .The first step in this project is to examine the past records since it provides clues to what might happen in the future.Plate tectonics, seabed geological conditions, paleoseismological evidences, historical earthquake datum,historical tsunami datum, sea depth, and so on, are the main basis of delineating potential tsunami source regions. The recurrence models used for the PTHA tend to favor the recurrence of earthquakes in individual fault segments, which limits the maximum magnitude to that allowable by the dimensions of the segments.Then the complexity and reasonablity will be chcked.After delineating the far-field and near-filed tsunamigenic earthquake sources,it enables us to deconstruct a tsunami model that is generated by an earthquake into a sum of individual tsunami waveforms by Green's functions from a set of subfaults that adequately describe the earthquake rupture. By pre-computing and storing the tsunami waveforms at points along the coast generated by each subfault for a unit slip, we can efficiently synthesize tsunami waveforms for any slip distribution by summing the individual subfault tsunami waveforms.This could input the numerical tsunamic model. The excitation and propagation of tsunamis in the water can be modeled using the shallow water wave approximation. We can solve the equation of motion numerically using a finite-difference method and the variable grid setup consists of a master grid with a coarse grid spacing and a number of nested finer grids with decreasing grid sizes around areas of interest will deployed. Then the simulation and the amplitude of the wage height could be calculated. The similar PSHA is adopted for processing the occurrence of the annual rate of occurrence. We also distinguish between two types of uncertainties，that is aleatory and epistemic and inclusion of those in both source and propagation models..The key deliverables will be the versatile Chinese probabilistic seismic tsunami hazard method and output maps,such the tsuanmigenic seismic zonation and inundation map, which could be tailed for the specific application.

近年我国海洋工程建设大量增加，地震海啸安全性评价应给于重视。本项目将收集、分析和整理地震海啸目录，开展我国沿海地震构造环境综合分析和海域海床地形特征分析，划分远海和近海潜在海啸源，建立地震发生概率与潜源识别模型，通过确定的潜在震源物理参数，开展地震海啸危险性分析；将设定地震破裂过程划分为若干子破裂断层，利用格林函数法，分别计算出子断层破裂产生的某一点的海啸波，模拟地震海啸初始发生位移场；基于海啸波的流体动力学方程，考虑海洋底部摩擦，建立浅水方程，开展不同参数下海啸传播与爬高模拟；以我国成熟的地震海啸危险性分析方法为基础，建立概率性海啸危险性计算方法，并对潜在海啸源区的不确定性进行分析，最后在地理信息系统平台下将数值模拟成果与基础数据集成。本研究思路和方法以及相应成果可以直接服务于我国沿海地震海啸危险性分析。

随着经济的快速发展，我国沿海地区的海啸风险不容忽视，开展海啸危险性分析工作十分必要。本项目针对我国地震海啸概率危险性分析方法开展研究，取得以下成果：.(1) 整理汇编了我国历史地震海啸目录、进行了沿海古海啸地质沉积调查；.(2) 进行了海啸初始位移场理论推导与计算，编写了相关程序；.(3) 开展了我国沿海地震构造环境综合分析和海域海床地形特征分析，划分了远海和近海潜在海啸源，确定了地震发生概率与潜源震源模型；.(4) 建立了我国沿海水深数字地形模型，验证了海啸产生、传播与爬高数值模型可靠性；提出了一种确定性方法，定性评估了我国沿海各地区的海啸危险性程度；.(5) 基于历史数据，评估了我国珠江三角洲地区的地震海啸危险性；.(6) 以我国成熟的地震海啸危险性分析方法为基础，建立了经典的地震海啸危险性概率分析方法（PTHA），以三门场点和大鹏场点为例，给出0.5米、1.0米、2.0米、3.0米海啸波高的10年、50年、100年超越概率；.(7) 分析了经典PTHA方法存在的问题，提出了一种基于蒙特卡洛技术的PTHA方法，以示例验证了方法可靠性并说明新方法可以较好地完善经典PTHA方法的不足之处；针对珠江口和台湾海峡典型场点，采用新方法开展PTHA评估，给出澳门、香港、大亚湾、汕头、厦门和泉州地区的不同海啸波高的重现期和100年超越概率，指出我国东南沿海地区的海啸危险性不容忽视；.(8) 开展了海洋水深数据对于海啸波高数值模拟的不确定性研究，发现目前开放的水深数据可满足海啸传播数值模拟的需要；.(9) 采用新提出的PTHA方法，对我国东南沿海地区1480个场点进行海啸危险评估，绘制了东南沿海地区海啸危险性图，包括波高1m、2m、3m、4m、5m以1年、10年、50年、100年为周期的超越概率分布图以及波高1m、2m、3m、4m、5m的重现期分布图。.本项目研究成果可作为沿海重大工程建设项目选址与规范的科学依据，提出的地震海啸危险性概率分析方法（PTHA）及编制的我国地震海啸危险性图，可作为我国海洋工程灾害评估和风险分析的重要技术理论。