中文摘要：

康拉德界面既是上地壳和下地壳的分界面,也是地壳内部花岗岩与玄武岩的分界面,其对于研究地壳稳定性、区域地质构造活动和地块演化历史等具有重要的指示意义。位于青藏高原东北缘的甘东南地区是多个地块的交汇区域,发育了多个断层和多次历史大地震。根据早期的研究结果,在构造活动比较强烈的大陆地壳内康拉德界面有可能是缺失的,但在该区域近震波形资料中清楚地记录到了振幅要比直达波大2~3倍的来自康拉德界面的震相。通过波形模拟和走时拟合,对这些震相进行了进一步核实。该结果提供了青藏高原东北缘存在康拉德界面的直接地震学证据。本文研究结果表明在构造活动活跃区域也可能存在康拉德界面,同时该结果对于该区域震相的准确识别、地震三要素的准确计算等也具有重要的参考价值。

英文摘要：

Conrad discontinuity,a boundary between the upper and the lower crusts and also a boundary between granite and basalt,plays an important role in the study of the stability of the earth's crust,the regional tectonic activity and the evolution of the block.The northeast margin of the Tibetan Plateau is located at the junction of several blocks and characterized by the development of large faults and strong historical earthquakes.The previous results hold that the Conrad discontinuity might be missing beneath the area with strong tectonic activity.In this study,several phases caused by the Conrad discontinuity,whose amplitudes are2~3times larger than those of the direct waves,were observed in southeast Gansu Province on the northeastern margin of the Tibetan Plateau.These phases were conformed to be derived from the Conrad discontinuity through wave form modeling and travel time fitting.The results not only provide direct evidence of seismology for the existence of the Conrad discontinuity on the northeastern margin of the Tibetan Plateau but also indicates that this discontinuity may also exist in the region of active tectonic activity.Moreover,this study is helpful to the accurate identification of the seismic phases of the regional earthquakes and the accurate calculation of the three elements of earthquake.