青藏高原东缘龙门山冲断带与四川盆地的现今构造表现:数字地形和地震活动证据

ACTIVE TECTONICS IN THE LONGMEN THRUST BELT TO THE EASTERN QINGHAI-TIBETAN PLATEAU AND SICHUAN BASIN:EVIDENCE FROM TOPOGRAPHY AND SEISMICITY

龙门山冲断带位于四川盆地与青藏高原东缘之间,其现今地貌和构造活动表现对于理解青藏高原东缘和四川盆地晚新生代的演化具有非常重要的意义。已有的认识多数是从“山”的角度得出的,我们尝试从“盆”这一角度,利用近20年来的地震活动资料和地震反射剖面,结合数字高程模型(DEM),通过三维可视化分析软件来探讨四川盆地及龙门山的地貌特征和现代构造活动表现。初步研究结果表明:1)龙门山的现今地貌和地震分布具有明显的南北分段性;2)青藏高原东缘活动块体边界表现为由龙门山南段北东向构造在安县附近转折为岷山的南北向构造;3)龙门山南段的现代地震活动已深入四川盆地内部,形成地壳规模的楔形逆冲构造,地震活动、现代地貌和地震反射剖面的证据揭示了龙门山及四川盆地存在晚新生代构造缩短的可能性。

The Longmen thrust belt is located between the Sichuan Basin and eastern margin of the Qinghai-Tibetan plateau, whose characterized topography and active structures in this area must be very important for understanding the tectonic evolution of the eastern margin of the plateau and the western Sichuan Basin from Late Cenozoic. So far, most of study on the area was based on the ＂plateau＂ point. We tried to analyze the features of the topography and active structures in the area by both of the earthquakes occurring in recent twenty years and Digital Elevation Model （DEM） by the help of 3d-visualization software. Our results were as follows. 1 ） By the characteristics of topography and the distribution of earthquakes, the Longmen Mts. could be divided into two segments, with a boundary near Anxian county. 2） the active margin of the eastern of the plateau extended northeastwards along the southern sector of the Longmen Mountains, then turned to the north along the Minshan Mts. near Anxian. 3）The earthquakes diffused into the western Sichuan Basin and appeared as a crustal wedge-shaped form toward the interior of the basin. In short words, all of the seismicity, topography and the seismic profile suggested the possibility of tectonic shortening in the Longmen Mts. and in the western Sichuan Basin from Late Cenozoic.