从青藏高原航磁资料分析尼泊尔8.1级地震构造背景

Analysis to Tectonic Background of M8.1 Nepal Earthquake Using Aeromagnetic Data in Qinghai-Tibet Plateau

利用小波分析处理青藏高原航磁资料,得到多尺度的航磁异常分布图。一阶小波结果反映地壳浅部的构造特征,在第Ⅰ和第Ⅱ缝合带位置,存在多条明显的北西西向弧形构造,由正负相间的磁异常带组成;在格尔木附近第Ⅳ缝合带位置存在近东西向的负磁异常条带。三阶小波结果反映地壳深部的构造特征,在约84°~91°E存在明显的近南北向的负磁异常条带,是研究区主要的深部构造特征。尼泊尔8.1级地震和3次7级强余震发生在近南北向的负磁异常条带的南端。该位置是近东西向的喜马拉雅构造带和近南北向的深部负磁异常条带的交汇部位。总体来说,青藏高原航磁资料揭示的浅部构造为多条近东西走向的带状构造,而深部构造是以近南北走向为主要特征,复杂的立交构造交汇部位是发生尼泊尔8.1级大地震的深部构造背景。

Using wavelet analysis method to process aeromagnetic data in the Qinghai-Tibet plateau, aeromagnetic anomaly maps with different scales are obtained. Results from the first order wavelet a- nalysis reveals the structure feature of shallow crust. In the suture Ⅰ and suture Ⅱ regions, there ex- ist several clear arcuate structures with NWW-striking, as shown by alternatively positive and nega- tive magnetic anomaly belts. There exists a negative magnetic anomaly belt with near EW-striking in suture Ⅳ near Golmud. The results from the third order wavelet analysis show the structure feature of deep crust. The main feature of deep structure in this region is represented by an obvious negative magnetic anomaly belt with near NS-striking between 87°N and 93°N. The Nepal M8.1 earthquake and its three strong aftershocks with magnitude 7 all occurred near the southern end of this magnetic anomaly belt, where the EW strike Himalaya tectonic belt intersects with the NS-striking negative magnetic anomaly belt. In general, the aeromagnetic data in Qinghai-Tibet plateau shows that, the main feature of shallow structures is near EW-striking, but the deeper structure is SN-striking. It im- plies that the intersection of the complex overpass structures is the tectonic background of the Nepal M8.1 earthquake.