东北亚地区地壳密度结构与垂向构造应力场

本文利用EIGEN-6C4重力数据和ETOPO1地形数据，在考虑物质密度横向不均匀的情况下，在东北亚地区展开地壳均衡研究，并重点分析了长白山的隆升机制.首先，针对穿越长白山和库页岛的两条近乎东西向的剖面（剖面A、B）展开详细研究，以CRUST1.0模型为初始条件，利用布格重力异常数据，基于Airy模型和Airy-Pratt模型分别反演了相应剖面的地壳密度结构，发现两剖面的地壳密度呈现一定程度的横向不均匀特性；接着基于上述密度结构和高程数据，利用Airy均衡理论计算了相应剖面的均衡面深度，并进一步比较莫霍面（Moho）和均衡面的差异，计算了剖面的垂向构造应力分布；然后，把上述方法应用到整个东北亚地区，计算了1°采样的21条东西向剖面的垂向构造应力，插值得到整个东北亚地区的垂向构造应力分布.结果表明，东北亚大部分地区垂向构造应力基本为零，总体处于均衡状态，长白山地区垂向构造应力为-15~-25 MPa，日本列岛垂向构造应力为-40~-50 MPa，太平洋海沟垂向构造应力为15~25 MPa；最后，本文运用自由空气重力异常导纳方法，计算了长白山地区的有效弹性厚度（T_e）和加载比，发现长白山地区的T_e为10 km，表明该地区的岩石圈较为柔软；加载比结果显示，岩石圈初始加载主要来自莫霍面，占总加载的78%，表明长白山的隆升主要源自地幔物质上涌.

Density structures of crust and vertical tectonic stress field of lithosphere in Northeast Asia

Considering the lateral density variation of crust, we investigate the isostatic state of Northeast Asia with the utilization of EIGEN-6C4 gravity data and ETOPO1 topography data, and analyze the uplifting mechanism of the Changbai Mountain. First, we study in detail two profiles in roughly east-west direction which stretch over Changbai Mountain and Sakhalin Island (profile A & B). Specifically, taking CRUST1.0 model as initial conditions, we inverse the density structure of Crust along the two profiles with Bouguer gravity anomalies, using Airy and Airy-Pratt isostasy theories, respectively. The results show that, to some degree, there is lateral inhomogeneity in the crust density structure along the profiles. Then, according to the inversed density structures and topography data we calculate the depth of isostasy along each profile. Based on the comparison of the depth of isostasy with the one of Moho, we calculate the vertical tectonic stress of the two profiles. And then, with the method illustrated above, we calculate the vertical tectonic stress along 21 profiles in exactly east-west direction within our study area, with sampling interval of 1 degree. By interpolating the above results we obtain the distribution of the vertical tectonic stress of the whole Northeast Asia. In total, the crust of Northeast Asia, whose vertical tectonic stress is about 0, is in isostatic state. Among which, the vertical tectonic stress at the Changbai Mountain is -(15~25) MPa, at Japan Islands is -(40~50)MPa, and at the Pacific trench is 15~25 MPa. Finally, we estimate the effective elastic thickness (T_e) and the load ratio of the area around the Changbai Mountain, using the method of Free-air gravity anomaly admittance. The result shows that the T_e of the Changbai Mountain is about 10 km, which mean that the lithosphere of the area is relatively soft. The initial load is mainly from the Moho, about 78% of total load, which suggest that the uplifting of the Changbai Mountain was mainly resulted from the uplifting of material of the Mantle.