通过大地测量手段观测的地震同震位移主要用于研究地震造成的物理特性和破坏机制，地震同震位移除了受震源参数影响，还受地球介质、地形起伏等因素影响。地形起伏和地壳介质参数均可直接量测得到，在地震正反演中，常常为简化模型忽视这些因素影响，传统使用接收高度函数法来减小地形的影响，但是在地形梯度变化较大时，会导致结果的不准确。随着计算机的发展，数值模拟方法在解决复杂地形和复杂介质的地球动力学问题中得到了应用。本文以2015年尼泊尔M_w7.8级地震为例，首先基于GNSS数据确定断层几何参数，然后使用变步长迭代法搜索最佳震源位置，分别研究了不同震源模型、地形因素和非均质因素等对正演地表同震位移的影响。本文研究结果可为地震观测台站以及GNSS观测站的合理布设给出参考。主要工作内容如下：

（1）利用数值模拟方法研究了地形因素和地下非均质因素对正演地表同震位移的影响。本文基于点源走滑型和逆冲型震源对地形、地下介质参数进行综合分析。基于两种震源模型在均匀介质和非均匀介质条件下，分别计算了地表高程为0km、1.5km和3km平坦地形以及高程为3km小山地形的地表同震位移。依据上述模型计算的地表同震位移分布结果，发现地形因素影响同震位移的分布形态，非均质因素影响同震位移的大小；

（2）给出了2015年尼泊尔M_w7.8级地震一个新的震源机制解。本文基于crust1.0地壳模型和真实地形构建尼泊尔地区网格模型，发现使用不同机构提供的震源机制解计算的地表同震位移与同震观测GNSS值相差较大。本文以同震GNSS观测值为约束，通过贝叶斯算法反演得到此次地震的断层几何参数，并采用变步长搜索法迭代搜索最佳震源位置；

（3）分别计算了点源震源的地形因素和非均质因素对地表同震位移的影响。本文研究结果发现2015年尼泊尔M_w7.8级地震的地形因素对同震位移影响为20~30%，其中采用SPECFEM3D计算为~20%，采用SPECFEMX计算为~25%；使用SPECFEM3D计算得到地壳非均质因素影响为5~10%；

（4）分别计算了面源震源下地形因素和非均质因素对地表同震位移的影响。本文研究结果发现2015年尼泊尔M_w7.8级地震的地形因素对同震位移影响为10~20%，其中采用SPECFEM3D计算为~15%，采用SPECFEMX计算为~18%；使用SPECFEM3D计算得到地壳非均质因素影响为3~5%。与点源震源相比，       点源震源会高估地形因素和非均质因素的影响。

The seismic coseismic displacements observed by geodetic means are mainly used to study the physical properties and damage mechanisms caused by earthquakes, which are influenced not only by the source parameters, but also by the Earth's medium and topographic relief. Topographic relief and crustal medium parameters can be directly measured. In the positive and negative seismic modeling, the problem around often ignoring the influence of these factors for the sake of simplifying the model is traditionally used to reduce the influence of topography by using the receiving height function method, but it will lead to inaccurate results when the topographic gradient changes greatly. With the development of computers, numerical simulation methods have been applied in solving geodynamic problems with complex terrain and complex media. In this paper, taking the 2015 Mw7.8 earthquake in Nepal as an example, we first determine the fault geometry based on GNSS data and search the optimal source location by variable step iteration method, and investigate the effects of different source models, topographic factors and non-homogeneous factors on the orthogonal surface coseismic displacement, respectively. The results of this paper can give reference for the reasonable deployment of seismic observation stations as well as GNSS observation stations. The main work is as follows:

(1) The effects of topographic factors and subsurface inhomogeneous factors on the orthogonal surface coseismic displacements are investigated using numerical simulation methods. This paper presents a comprehensive analysis of topographic and subsurface medium parameters based on point-source walking-slip and retrograde-type earthquake sources. Based on the two source models, the surface coseismic displacements are calculated for 0 km, 1.5 km and 3 km flat terrain and 3 km hill terrain under the conditions of homogeneous and inhomogeneous media, respectively. Based on the results of surface coseismic displacement distribution calculated by the above models, it is found that topographic factors affect the distribution pattern of coseismic displacement and inhomogeneous factors affect the magnitude of coseismic displacement.

(2)  A new seismogenic mechanism solution is given for the 2015 Mw7.8 earthquake in Nepal. In this paper, we construct a grid model of the Nepal region based on the crust1.0 model and real topography, and find that the surface coseismic displacements calculated using the solutions of the earthquake source mechanism provided by different institutions differ significantly from the coseismic observed GNSS values. In this paper, the fault geometry parameters of this earthquake are obtained by Bayesian algorithm inversion with the constraint of coseismic GNSS observations, and the optimal source location is searched iteratively using the variable step search method.

(3) The effects of topographic and inhomogeneous factors of the point source earthquake source on the surface coseismic displacement were calculated separately. The results of this paper found that the topographic factors of the 2015 Mw7.8 earthquake in Nepal had an effect of 20-30% on the coseismic displacement, including ~20% using SPECFEM3D and ~25% using SPECFEMX; the effect of crustal inhomogeneous factors was 5-10% using SPECFEM3D.

(4) The effects of topographic and inhomogeneous factors on surface isoseismic displacements were calculated separately for face-source earthquake sources. The results of this paper found that the topographic factors of the 2015 Mw7.8 earthquake in Nepal had an influence of 10-20% on the coseismic displacements, including ~15% using SPECFEM3D and ~18% using SPECFEMX; the influence of crustal inhomogeneities was 3-5% using SPECFEM3D. Point source seismic sources can overestimate the effects of topographic and inhomogeneous factors compared to point source sources.