利用虚拟地震测深法约束青藏高原东北缘及周边地区地壳厚度

青藏高原东北缘作为高原向外扩张的最前缘地区，代表了高原最新的变形状态，是研究青藏高原变形加厚的关键地区.本文利用"中国地震科学台阵探测"项目在南北地震带北段布设的密集宽频带流动台阵资料，采用虚拟地震测深方法（VDSS），对青藏高原东北缘及周边地区的地壳厚度进行了研究，以期为研究青藏高原东北向扩展的前缘位置，以及扩展的动力学模式等提供地球物理学依据.波形模拟的结果显示，研究区地壳厚度变化剧烈.其中，祁连和西秦岭地块内地壳厚度存在明显的东西向横向变化，以103°E为界，东部地区为45~50 km，而西部地区地壳已明显增厚，约达到55 km以上.与祁连造山带相邻的阿拉善块体南缘地壳也明显加厚，接近55 km，而阿拉善块体内部地壳厚度约为45~50 km.与其他研究地区相比，鄂尔多斯地块地壳相对要薄，但整体而言，鄂尔多斯地块地壳呈现南北薄（约45 km）、中央厚（约50 km）的形态特征.此外，在六盘山断裂带台站下方观测到复杂的SsPmp震相，推测为双Moho界面结构.结合其他地球物理学证据，我们认为青藏高原东北缘地区地壳增厚方式以均匀缩短增厚为主，且高原向北东扩展的前缘已越过祁连山北缘断裂，进入阿拉善块体南缘地区.

Constraints on the crustal thickness in the northeastern Tibetan Plateau and adjacent regions from virtual deep seismic sounding

The northeastern margin of the Tibetan plateau, as the leading edge of the plateau extension, represents the latest deformation of the plateau, which is the key to understand the mechanism of crustal thickening and deformation of the Tibetan plateau. This work estimated the crustal thickness of the northeastern Tibetan plateau and adjacent by the Virtual Deep Seismic Sounding (VDSS) method using the data of the "ChinArray" project, aiming to provide geophysical constraint on the northeastern leading edge of the Tibetan plateau and the dynamic model of the extension. Our results show that the crustal thickness changes dramatically in different tectonic units. Systematic variations of crustal thickness in east-west direction exist within the Qilian and West Qinling orogenic belts. Bounded by about 103°E, the crust is about 45~50 km in the east and more than 55 km in the west. The crust is also thicker (nearly to 55 km) under the transitional region between the Alxa block and the Qilian orogenic belt, while about 45~50 km beneath the central Alxa block. In comparison, the Ordos block has a thinner crust, of which the thickness tends to increase from northern and southern parts (about 45 km) to the central region (about 50 km). In addition, complex SsPmp phases are observed under the Liupanshan station, suggesting a double Moho. Combined with other geophysical evidence, we speculate that the outward expansion of the northeastern Tibetan plateau has evolved by distributed crustal thickening and removal of the lower crust, and the frontier of northeastern growth has already reached to the southern margin of the Alxa block.