南北构造带中北部地下低速体的分层联合反演及梯度分布

南北构造带中北部地处中国大陆地质构造东西分界处，地下深浅部构造复杂且地震灾害严重。该区域广泛分布的地震波低速异常体在壳幔解耦和孕震构造等关键地球动力学问题中扮演着重要的角色。受限于以往该区域天然地震和台站分布，该区域深浅部的低速体分布细节仍未达成共识，制约了对其构造边界和造山模式等深入研究。本研究拟在新近密集台阵的基础上，采用分层地震联合成像反演的策略，首先结合天然地震和人工地震数据的初至P波和后续震相PmP获取精细的三维地壳P波速度结构，再对岩石圈深部的近远震联合反演结果进行地壳校正，最后进行速度结构的三维相对梯度分析。旨在降低浅部剧烈构造和目标模型外带来的误差干扰，提高对岩石圈深浅部的低速现象的解析度。研究结果有助于刻画南北构造带中北部地区深部构造边界，对于了解该地区大陆地块间的相互作用和构造成因具有重要意义。

The mid-north part of the north-south tectonic belt with the highest level of seismicity in Mainland China is the main tectonic boundary between the east and west parts of Chinese continent, where tectonic structure underground is complicated and need to be updated. Widespread low-velocity zones (LVZs) play an important role of regional geodynamic problem, including seismogenic structure and decoupling between the crust and the mantle. Limited by inadequate earthquakes and loose seismic station, the details of LVZ underground remain controversy, which confine intensive study on regional tectonic boundary and orogenic model. Several dense seismic arrays have been recently deployed in the mid-north part of the north-south tectonic belt and recorded a large number of seismic events that will benefit this project significantly. Based on the strategy of the hierarchically seismic joint imaging, we plan to firstly apply high-quality first P wave and later PmP-wave arrival-time data from local earthquakes and seismic explosions to determine a high-resolution crustal structure, then take a crustal correction for inversion of deep structure of our study area by jointly using arrival-time data from local and teleseismic events, and finally carry out a 3-D relative gradient analysis for velocity anomaly structure. So that we can reduce the uncertainty of tomographic image that induced by severely heterogeneous crust and outside space of model, and improve the resolution of LVZs in whole lithospheric space. The result will help to depict deep tectonic boundary below the mid-north part of the north-south tectonic belt, and improve understanding for interaction among regional tectonic blocks and cause of tectonic activities.