龙门山及其邻区构造的不稳定性一直是地质地球物理学家关注的焦点。布格重力异常急剧变化是该区最显著的地球物理场特征，它被广泛地用于研究地壳结构。鉴于重力资料分辨率较低，人们常常根据已知密度界面、地震波速度等信息建立“剥皮”模型约束重力资料的解释。本申请项目提出将地壳平均波速比作为“剥皮”模型的一部分，约束重力资料研究龙门山地区的地壳三维密度结构。我们将在前人实验研究的基础上，首先开展波速比与密度的转换关系研究，确定地壳平均波速比的重力场模拟方法。在此基础上，利用研究区地壳平均波速比、沉积层与地壳厚度资料，建立重力场“剥皮”模型。最后，对剩余重力异常实施反演建立地壳三维密度结构。通过本项研究，构建波速比与密度之间的量化关系，厘清地壳平均波速比模拟重力场的机制与影响因素，对促进地壳平均波速比与重力资料的交叉研究具有重要的科学意义，同时得到的地壳三维密度模型对研究龙门山地区的地震活动性具有现实意义。

The instability of the crustal structure in Longmenshan and adjacent regions has always been the focus of the geologists and geophysicists. As one of the most significant geophysical field characteristics, Bouguer gravity anomalies vary drastically across Longmenshan fault zone, and are used widely in crust structure research. Since the gravity resolution is relatively low, usually the “Layer stripping” model based on the known information, e.g. the density interface and the seismic velocity, is used to constrain the gravity data. We propose to apply the crustal Vp/Vs as a part of the “Layer stripping” model to constrain the gravity data to invert the 3D density model in Longmenshan and adjacent regions. We first plan to study the relationship between the crustal Vp/Vs and the density based on the previous experimental studies, and then derive the gravity modeling method based on the crustal Vp/Vs. Secondly, modeling the sedimentary gravity effect, the Moho gravity effect, and the gravity effect from the crustal Vp/Vs. We correct the mentioned three parts of the gravity effects from the observed Bouguer gravity, and finally, use the residual anomaly to invert the 3D density structure. We hope that this study would improve the application of the crustal Vp/Vs on the gravity data interpretation, and the obtained 3D crustal density model in Longmenshan and adjacent regions shows the significance to study the local earthquake activity.