用GPS分析天山现今地壳变形与应变率场

PRESENT-DAY CRUSTAL DEFORMATION AND STRAIN RATE FIELD OF TIANSHAN MOUNTAIN ANALYZED WITH GPS DATA

基于中国地壳运动观测网络1999-2013年和中国大陆构造环境监测网络2009-2013年的GPS区域网观测资料,并结合境外天山、帕米尔等地区公开发布的速度场结果,获取整个天山及邻区较为完整的地壳运动图像以及应变率场分布特征。初步结果表明：1）天山地区现今应变率场分布的整体特征与该地区长期的地质构造背景具有一定的继承关系,天山以近南北向挤压缩短变形为主要特征,主压应变率由其西段（77°E附近）的约45×10-9/a,逐渐降至东段（86°E附近）的约10×10-9/a;2）天山西南部的帕米尔高原北缘逆冲断裂带及其北侧的阿莱山脉附近为面压缩区,主压应变率约为（50-60）×10-9/a,面膨胀率约为（40-50）×10-9/a,与已有GPS剖面观测到的该区域（10-15）mm/a的地壳缩短速率十分一致;3）与塔里木盆地相邻的帕米尔高原东部地区（38°N附近）,其现今地壳活动、应变率场分布与该地区目前处于拉张的地震、地质构造背景有很好的一致性,主应变率和面膨胀率显示存在一定程度的拉张变形,拉张应变率约为（10-20）×10-9/a,方向为近东西向;4）最大剪应变率结果显示天山地区存在一定程度的剪切变形,最大剪应变率高值区对应于西南天山的帕米尔北缘逆冲断裂带附近,幅度最大值约为40×10-9/a;5）另一最大剪应变率高值区位于天山西部（78°E附近）,幅度约为30×10-9/a。

Using GPS data of Crustal Movement Observation Network of China observed from 1999 - 2013 and data of Continental Tectonic Environment Monitoring Network of China from 2009 -2013, combined with other published GPS velocity field were analyzed and a more complete horizontal velocity field covering the Tianshan mountain and its vicinity was obtained. Preliminary results Indicare that present-day strain rate field is consistent with the long-term tectonic settings in the Tianshan mountain and its vicinity. The deformation of Tianshan mountain is mainly characterized by nearly north-south crustal shortening, and the principal compressive strain rate is about 45 × 10^-9/a in the western part （-77°E） ,and about 10 × 10^-9/a in the eastern part （-86°E）. The northern Pamir thrusting fault zones and its northern Trans-Alay Range are in a compression, state, with a principal compressive strain rate of about（50- 60） × 10^-9/a and with dilation rate of about（40- 50） ×10^-9/a, consistent with previous studies of 10 - 15mm/a crustal shortening rates observed from GPS velocity profiles in this region. In the eastern part of Pamir （-38°N） ,which is adjaeent to the Tarim Basin, prineipal strain rate and dilation rate demonstrate that there is certain extension with a rate of about（ 10 -20） ×10^-9/a. Direction of the extension is nearly westeast, which is consistent with the extensional strain state observed from previous geologic and seismic studies in this region. The other maximum shear strain rate,40 × 10^- 9/a,appears in the northern Pamir thrusting fault zones,and another high value,30 × 10^-9/a,appears in the western Tianshan mountain （-78°E）.