Crustal P-wave velocity structure in the northeastern margin of the Qinghai-Tibetan Plateau and insights into crustal deformation
Crustal P-wave velocity structure in the northeastern margin of the Qinghai-Tibetan Plateau and insights into crustal deformation
复制标题
青藏高原东北缘地壳纵波速度结构及地壳变形认识
DOI：
10.1007/s11430-017-9227-7
复制
发表时间：
2018-07
期刊：
影响因子：
--
通讯作者：
Liu BJ
中科院分区：
文献类型：
--
作者：
Wang Shuaijun;Liu Baojin;Tian Xiaofeng;Liu Baofeng;Song Xianghui;Deng Xiaoguo;Sun Yinan;Ma Cejun;Yang Yudong;Liu BJ
青藏高原东北缘、鄂尔多斯地块和阿拉善地块之间的过渡区，也是南北地震带的北段，具有相当高的地震活动水平和强震危险性。针对该区特殊的构造环境和深部构造背景，利用两条地震广角反射/折射剖面进行双重约束，以便更可靠地获得研究区各地块浅、深部地壳及其边界的精细速度结构特征，进一步探讨历史强震地震区的孕震环境。本文对这两条剖面的P波资料进行了处理和解释，并通过走时正演模拟建立了沿这两条剖面的二维地壳速度结构模型。结果表明，两条地震剖面采集的不同地块在速度结构、壳内界面形态和地壳厚度等方面存在较大差异。沿兰州-惠安布-榆林地震测深剖面(L1)的地壳厚度由鄂尔多斯地块西缘的∼43公里增加到祁连地块西缘的∼56公里。鄂尔多斯地块的速度等值线变化平缓，地壳平均速度约为6.30公里S−1，而祁连地块和弧形构造带的地壳速度结构变化较大，平均地壳速度比鄂尔多斯地块低约0.1公里S−1。此外，在祁连地块和弧形构造带的地壳中还发现了不连续的低速体(LVZ1和LVZ2)，其速度比周围的S−1低0.1-0.20公里。沿L2(铜川-惠安布-阿拉善左旗地震测深剖面)和L1剖面，鄂尔多斯地块的平均地壳厚度一直估计在43公里左右。鄂尔多斯地块沿L1剖面具有典型的稳定克拉通构造特征，其地壳界面和速度等值线变化平缓，而沿L2剖面的地壳结构则表现出相当复杂的变化。这表明鄂尔多斯地块内部存在明显的地壳结构差异。贺兰山-祁连地块和银川盆地的地壳结构以“隆降”起伏为特征，表现出局部挤压变形的特征。此外，贺兰山以下的中下地壳存在高、低速交替的低速带，速度比周围地区低约0.15-0.25kmS−。阿拉善地块的地壳厚度约为49公里，上地壳和中下地壳层速度等值线变化明显。两条地震测深剖面L1和L2的复杂地壳速度结构图像揭示了历史强震发震地震带不同构造块体之间的构造差异、耦合关系和速度结构特征。本研究的成像结果为进一步了解研究区的孕震环境和孕震机制提供了精细的地壳结构信息。
The transitional area between the northeastern margin of the Qinghai-Tibetan Plateau, Ordos Block and Alxa Block, also being the northern segment of the North-South Seismic Belt, is characterized by considerably high seismicity level and high risk of strong earthquakes. In view of the special tectonic environment and deep tectonic setting in this area, this study used two seismic wide-angle reflection/refraction cross profiles for double constraining, so as to more reliably obtain the fine-scale velocity structure characteristics in both the shallow and deep crust of individual blocks and their boundaries in the study area, and further discuss the seismogenic environment in seismic zones with strong historical earthquakes. In this paper, the P-wave data from the two profiles are processed and interpreted, and two-dimensional crustal velocity structure models along the two profiles are constructed by travel time forward modeling. The results show that there are great differences in velocity structure, shape of intra-crustal interfaces and crustal thickness among different blocks sampled by the two seismic profiles. The crustal thickness along the Lanzhou-Huianbu-Yulin seismic sounding profile (L1) increases from ∼43 km in the western margin of Ordos Block to ∼56 km in the Qilian Block to the west. In the Ordos Block, the velocity contours vary gently, and the average velocity of the crust is about 6.30 km s−1; On the other hand, the velocity structures in the crust of the Qilian Block and the arclike tectonic zone vary dramatically, and the average crustal velocities in these areas are about 0.10 km s−1lower than that of the Ordos Block. In addition, discontinuous low-velocity bodies (LVZ1 and LVZ2) are identified in the crust of the Qilian Block and the arc-like tectonic zone, the velocity of which is 0.10–0.20 km s−1lower than that of the surroundings. The average crustal thickness of the Ordos Block is consistently estimated to be around 43 km along both Profile L2 (Tongchuan-Huianbu-Alashan left banner seismic sounding profile) and Profile L1. In contrast to the gently varying intra-crustal interfaces and velocity contours in the Ordos Block along Profile L1, which is a typical structure characteristic of stable cratons, the crustal structure in the Ordos Block along Profile L2 exhibits rather complex variations. This indicates the presence of significant structural differences in the crust within the Ordos Block. The crustal structure of the Helan Mountain Qilian Block and the Yinchuan Basin is featured by “uplift and depression” undulations, showing the characteristics of localized compressional deformation. Moreover, there are low-velocity zones with alternative high and low velocities in the middle and lower crust beneath the Helan Mountain, where the velocity is about 0.15–0.25 km s−1lower than that of the surrounding areas. The crustal thickness of the Alxa Block is about 49 km, and the velocity contours in the upper and middle-lower crust of the block vary significantly. The complex crustal velocity structure images along the two seismic sounding profiles L1 and L2 reveal considerable structural differences among different tectonic blocks, their coupling relationships and velocity structural features in the seismic zones where strong historical earthquakes occurred. The imaging result of this study provides fine-scale crustal structure information for further understanding the seismogenic environment and mechanism in the study area.
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影响因子：
12.1
作者：
Zhang, Zhongjie;Yang, Liqiang;Teng, Jiwen;Badal, Jose
通讯作者：
Badal, Jose
影响因子：
2.9
作者：
Mingjun Liu;W. Mooney;Songlin Li;N. Okaya;S. Detweiler
通讯作者：
Mingjun Liu;W. Mooney;Songlin Li;N. Okaya;S. Detweiler
DOI：
10.1007/s11430-017-9092-8
发表时间：
2017-09
期刊：
Science China Earth Sciences
影响因子：
--
作者：
Y. Ling;Ling Chen;Zigen Wei;M. Jiang;Xu Wang
通讯作者：
Y. Ling;Ling Chen;Zigen Wei;M. Jiang;Xu Wang
影响因子：
2
作者：
C. Qin
通讯作者：
C. Qin
影响因子：
--
作者：
Q. Deng;Yuhua Liao
通讯作者：
Q. Deng;Yuhua Liao