深地震反射剖面揭示的海原断裂带深部几何形态与地壳形变

由于活动的青藏高原不断的隆升和推挤作用,在西南向东北的推挤作用和周缘块体的阻挡以及东北缘内部块体挤压形变的作用下,形成了多个走向不同的青藏高原东北缘构造体系.新生代构造变形和地震活动强烈,区内分布多条大型深断裂带.海原断裂是青藏高原东北缘发育的弧形活动断裂带中规模最大、活动最为强烈的一条左旋走滑型断裂带,是重要的大地构造区边界,也是控制现今强震活动的活断层.本文利用2009年完成的高分辨率深地震反射剖面的北段资料,对其进行初步构造解释,揭示出海原断裂带的深部几何形态和其两侧地壳上地幔细结构.结果显示海原断裂并不是简单的陡立或者较缓,其几何形态随着深度变化.在海原断裂之下的Moho并未错断的反射特征显示海原断裂并不是直接错断莫霍面的超壳断裂.海原断裂带及两侧岩石圈结构和构造样式的研究为探讨青藏高原东北缘岩石圈变形机制提供地震学依据.

Deep structure geometry features of Haiyuan Fault and deformation of the crust revealed by deep seismic reflection profiling

Because of the incessant uplifting and pushing of the active Qinghai-Tibet Plateau, a number of structural systems with different trends on the Qinghai-Tibet plateau northeastern margin are formed under the joint action of northeastward pushing, blocking of circumjacent blocks, and the squeezing and deformation in the internal block of the northeastern margin of the plateau. Cenozoic tectonic deformation and seismic activity is intense, several large deep fault zones are distributed in the area. The Haiyuan fault is a left strike-slip fault zone with the strongest activities and the largest scale among the arc and active fault zones of the northeastern margin of Qinghai-Tibet Plateau, which is an important tectonic zone boundary fault and also an active fault controlling earthquake activity. The northern part of the high-resolution deep seismic reflection profile completed by CAGS in 2009 was used in this paper, and the preliminary interpretation revealed the deep geometry of the Haiyuan fault zone and the fine structure of the crust and upper mantle of its both sides. The results showed that the Haiyuan fault is not simply steep or moderate, but its geometric shape changes with depth . The continuous reflection characteristics of the Moho under the Haiyuan fault show that Haiyuan fault is not a trans-crust fault breaking up the Moho directly. The research results provide seismological basis for studying the lithosphere deformation mechanism of the northeastern margin of the Qinghai-Tibet Plateau.