【作者】 胥广银；

【导师】 高孟潭；

【作者基本信息】 中国地震局地球物理研究所 ， 固体地球物理学， 2003， 博士

【摘要】 在目前的地震危险性分析方法中，潜在震源区是二维的。在潜在震源区内，地震的震源被简化成点或线，并且是均匀分布的。实际上，地震震源在三维空间上是不均匀分布的，这种不均匀分布对近场范围内场点的地震危险性的影响是显著的。对于较大震级地震，由于震源尺度较大，近场范围内场点的地震危险性受地震破裂几何产状的影响十分显著，这种情况下将地震震源简化成点或线显然是不合理的。针对这些问题，考虑到资料研究的程度，本文提出了三个模型分别描述潜在震源的三维空间分布特征或三维空间展布特征，并研究其在地震危险性分析中的应用。 通过对1970年以来、定位精度为Ⅰ-Ⅱ类、含有深度定位信息的浅源地震进行分析，得出了我国浅源地震震源深度分布的一般特征。并且，为了研究地震震源深度分布的分区特征，针对不同地区的地震分别给出了描述其震源深度分布的近似函数—正态分布函数。为了描述潜在震源的深度分布，我们假设未来可能发生的地震震源的深度分布也遵循类似的特征。通过综合利用已有的研究成果，并结合目前地震危险性概率分析中的研究状况，我们提出了两个描述潜在震源三维空间分布的模型，探讨它们在地震危险性概率分析方法中的应用。在弱震和中等强度地震活动性分析模型(胥广银，1998)的基础上，构建了反映近期中小地震空间分布特点的潜在震源三维空间分布模型；利用潜在震源区内部地震活动的非均匀分布模型(高孟潭、胥广银，1996)我们构建了反映较大震级地震空间分布集中度高特点的潜在震源体模型。在以中小地震活动为主的长江中游地震带我们选定一个计算区域，采用反映中小地震活动三维空间分布特征的地震危险性概率分析方法进行了对比研究；在地震活动较强、地震地质构造资料比较丰富的北京附近地区，我们选定一个区域，对于6级以上的潜在地震采用潜在震源体模型、对于6级以下的潜在地震采用中小地震活动三维空间分布的模型进行地震危险性概率分析的实践研究。考虑到地震震源深度分布由于资料的精度和数量等可能带来的不确定性，我们还分别采用了单一震源深度模型、震源深度均匀分布模型，通过改变地震震源深度的分布函数进行对比研究，得出如下结论： (1)考虑潜在震源三维空间分布的地震危险性概率分析方法，对于场点的地震危险性分析和区域地震区划来说具有重要意义。 (2)因近场潜在震源深度的变化，对于场点的地震危险性概率分析结果有明显的影响。由于中小地震的震源尺度较小，可以将潜在震源简化成点源，并考虑震源深度参数。随着地震观测技术的不断发展，地震震源深度的定位精度不断提高，考虑地震深度对地震危险性分析结果的影响会更趋合理。 (3)虽然在地震危险性概率分析中考虑震源深度分布的方法有多种，但是各种方法所得的结果的差异不明显。采用任意一种方法的地震危险性分析结果在工程上都是可以接受的。考虑到计算的方便，我们可将震源随深度的分布简化为平均震源深度。 (4)由于构造活动在空间上是不均匀的，同一地震带内不同的潜在震源区可能有不同的平均震源深度。因此，应该对近场潜在震源区进行专门的研究，并确定其平均震源深度。 震源物理的研究成果表明，地震造成的场点地震动峰值的大小，主要与场点到地震破裂面最近的破裂点有关。如果只采用点源或断层线源模型来描述潜在震源，在地震动衰减关系中仍使用震中距、震源距、甚至断层距，己不能够合理描述地震对场点地震动峰值参数的影响。为了在地震危险性概率分析中探讨高震级潜在震源的考虑方法，我们提出了潜在地震破裂面源模型。通过将这种分析方法应用到发生过台湾集集7.6级地震的车笼埔断层上，我们得出以下结论:(l)从震源物理理论的角度出发，采用潜在地震破裂面源模型是合理的。因为它可_以模拟地震破裂面与地震动影响场的三维展布特征，·尤其适用于较大震级地震的近场区域石(2)潜在地震破裂面源的大小、产状，对近震源场点的地震危险性分析和地震区划结果有明显的影响。(3)合理考虑潜在地震破裂面源模型是今后地震危险性分析方法研究的发展趋势。随着资料的不断丰富和研究程度的不断提高，我们相信，不久将会采用断层破裂面模型。更多还原

【Abstract】 Potential source zones are 2-D in the current probabilistic seismic hazard analysis methods. Within these zones, earthquake focuses are simplified as points or lines and they distribute uniformly. In fact, earthquakes distribute non-uniformly in 3-D space, these non-uniform distributions have great influence on seismic hazard of sites near earthquake focuses. The geometric sizes and its attitudes of rupture surfaces that generate earthquakes with great magnitude have great influence on seismic hazard of near sites, and it is unreasonable if we still take the focuses as points or lines. Under this circumstance, we proposed three models to characterize the.3-D distributions of potential earthquakes with low to middle magnitude and the 3-D spreads of potential earthquakes with large magnitude, and studied their applications on probabilistic seismic hazard analysis.The general characteristics of earthquake hypocenter depth distributions in China were given by analyzing shallow earthquakes (depth < 70 km), which were recorded with modern instruments and contain depth information with orientation precision 1 and 2 after 1970. Different depth distribution functions to which focuses yield, normal distribution functions, were given for different geotectonic zones to depict the difference among hypocenter depth distributions in different zones. It is assumed that depth distribution of future potential hypocenters yield to the distribution characteristics similar to the above-mentioned ones. Considering the degree to which the basic data had been studied, in order to utilize the recent obtained research results, two methods which take into account the 3-D spatial distribution characteristics of seismic potential sources are proposed for improving the current probabilistic seismic hazard analysis methods. According to the seismicity model of low to moderate earthquakes (XU Guangyin, 1998), we constructed a 3-D potential source distribution model to characterizing the spatial distributions for low to moderate earthquakes. According to the non-uniform distribution models of earthquakes in potential sources (GAO Mengtan and XU Guangyin, 1996), we constructed a potential seismic source body model to depict the distribution characteristics of spatial concentration for large earthquakes. In this paper the seismic hazard analysis method that takes into account 3-D spatialhypocenter distributions of low to moderate earthquakes was adopted to calculate the seismic hazard for selected sample areas in Yangtse River middle reach seismic province where seismicity is characterized by low to moderate earthquakes. The seismic hazard analysis method applying potential seismic source body model was adopted for potential earthquakes with magnitude 6 and greater, and the method considering 3-D spatial hypocenter distributions of low to moderate earthquakes was also adopted for potential earthquakes with magnitude less than 6 in Beijing and adjacent areas where seismicity is very strong, rich in seismotectonics data and the delineated potential sources are relatively creditable. Considering uncertainties of precision and quantity of earthquake data used in statistical hypocenter depth distribution studies, we also adopted single-depth model and uniform-depth model of earthquake hypocenters as comparative models for method study of considering hypocenter depth factor in probabilistic seismic hazard analysis methods and we drew the following conclusions.(1) Probabilistic seismic hazard analysis methods that take into account 3-D spatial distributions of potential hypocenters have-great influence on results of seismic hazard analysis and regional seismic zoning.(2) The depth change of future potential hypocenters have great influence on the results of probabilistic seismic hazard analysis of sites near potential hypocenters, so the probabilistic seismic hazard analysis in which potential hypocenters are simplified as point sources should take into account the parameter of hypocenter depth, especially for earthquakes with small or m更多还原