山西地震带北部地震危险区强地面震动预测模型研究

Strong ground motion is the significant driving force and main cause of damage to buildings, ground rupture and collapse, landslides and other disasters resulted from earthquakes. Accurate simulation of such shaking has been proven to be an effective way to analysis of surface damage process, forecast and prevention of seismic disaster by numerous studies. Among them the stochastic finite-fault simulation is one of the most widely used approaches for analysis of ground motion, represented by the EXSIM (Extended Stochastic Finite-fault Simulation Model) currently. This model adopts a source spectrum characterized by the dynamic corner-frequency and introduces the concept of scale factor and percentage of pulse sub-faults. It, therefore, can be applied for earthquakes with a wide scope of magnitudes. However, in the aspect of source rupture process the model just defines the initial point, duration and percentage of rupture sub-faults, no improvement in expressing the source rupture directivity effect has been carried out so far. Such influence of rupture directivity on near field ground motion is significant, even for small earthquakes (e.g., small earthquakes at Parkfield). The project will first attempt to improve the rupture directivity effect of the stochastic finite-fault simulation approach based on currently existing models, to make it more in line with the fault rupture. We will then take the northern part of the Shanxi seismic belt, which has been defined as one of the national key seismic risk regions for many years, as an example, to construct the regional ground motion prediction model (GMPM). Earthquake strong ground motion simulation is still a relatively young science at present, and research on its models is to explore the meaning. Additionally, the first GMPM constructed for northern part of the Shanxi seismic belt can provide theoretical evidence for further evaluation of seismic hazard and disaster prevention of the national key seismic risk region in the future.

强地面震动是造成建筑物破坏、地面破裂和塌陷、山体崩塌、滑坡等灾害的动力和主因。准确模拟该震动是分析其对地表的破坏过程以及预测、预防地震灾害的有效途径。随机有限断层法是目前常用的地震动模拟方法之一，以EXSIM为代表。该模型采用了含有动力学拐角频率的震源谱，引入了标度因子与脉冲子断层百分比的概念，有较宽的震级适用范围。但在震源破裂方面只强调了子断层破裂的初始点、持时与百分比，断层破裂方向性这一重要近场效应的表达未有改进。本项目旨在现有模型基础上，首先尝试改进其在震源破裂方向性效应上的表达，使之更符合断层破裂的实际情况；然后以地震动模拟研究较少的山西地震带北部全国地震重点危险区为研究对象，构建其强地面震动预测模型。地震动模拟目前仍是一门较新的科学，对其模型的研究具有探索意义；首次构建山西地震带北部地震危险区的强地面震动预测模型，可为该地区的地震危险性评价及震害防御提供理论依据。

强地面震动是造成建筑物破坏、地面破裂和塌陷、山体崩塌、滑坡等灾害的动力和主因。准确模拟该震动是分析其对地表的破坏过程以及预测、预防地震灾害的有效途径。本项目立足现有研究成果，以山西地震带为研究对象，开展了多参数强地面震动预测模型研究与地震危险性评估工作。主要研究内容包括：1）国内外代表性强地面震动模型及算法的对比研究，厘清不同模型的理论基础、优点与不足；2）模型中各参数物理意义及其对模拟结果影响分析，厘清强各参数对模拟结果影响的方式与影响程度；3）山西地震带预测模型构建及程序代码编写；4）山西地震带衰减模型及土层场地类别分析，5）山西地震带地震危险性评估。通过对强地面震动预测模型的研究，构建了多参数预测模型，揭示了基岩条件下，震级大小、障碍体、破裂机制、破裂起始点、破裂持续时间、破裂速度、破裂方向性、应力降和介质因子9个参数对结果的影响最为显著；对不同频率下强地面震动响应谱结果分析发现，在震源参数中震级大小、障碍体、破裂机制确定的情况下，应力降和介质因子是影响高频地震动衰减的主因，而低频地震动则受到破裂持续时间与破裂速度的显著影响。此外，对山西地震带地震灾害评估结果揭示了山西地震带的北部、临汾盆地以及运城盆地南部地震危险性相对较高，近距离的中强地震是造成震灾的主要原因。强地面震动模拟仍然是一门较新的方向，围绕强地面震动预测模型的持续深入研究是地震学领域一个具有实际防灾减灾意义的学术问题；地震危险性评估有助于进一步理解山西地震带潜在的强震危险性，为该地区抗震设防提供理论依据。