| 南北地震带北段的地壳速度结构及其构造启示 |
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| 引用本文： | 郭慧丽,丁志峰. 南北地震带北段的地壳速度结构及其构造启示[J]. 地震学报, 2018, 40(5): 547-562. DOI: 10.11939/jass.20180006 |
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| 作者姓名： | 郭慧丽 丁志峰 |
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| 作者单位： | 1.中国北京 100081 中国地震局地球物理研究所 |
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| 基金项目： | 国家自然科学基金（41704060）、中国地震局地球物理研究所基本科研业务专项（DQJB15A03）和国家公益性地震行业科研专项（201308011）共同资助 |
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| 摘 要： | 收集和拾取了“中国地震科学台阵”探测项目在南北地震带北段布设的680个流动地震台站和中国地震台网217个固定台站所记录的地震事件的P波和S波初至到时，通过层析成像研究获得了南北地震带北段水平网格间距为0.33°×0.33°的地壳P波和S波速度分布。结果显示:在30 km深度上青藏高原东北部表现为显著的整体性低速异常，低速异常区向南延伸至龙门山断裂，以106°E为界线将秦岭造山带分为西侧的低速异常和东侧的高速异常，并沿银川—河套地堑向东北展布，向北穿过河西走廊，在阿拉善地块表现为低速异常，这可能暗示了青藏高原向东的扩展被较为坚固的四川盆地和秦岭造山带阻挡，而向北的扩展可能影响到了河西走廊至阿拉善地块，并沿银川—河套地堑影响到鄂尔多斯西北缘；在50 km深度上，阿拉善地块、祁连造山带东段显示高速异常，有可能是阿拉善地块向祁连东段下方俯冲所致。研究区内大部分地震分布在P波和S波高低速异常相间及速度剧烈变化的地区，M≥6.0强震几乎全部投影在30 km深度的低速异常区域内，说明强震发生的背景可能与地震源区下方的低速区有关。
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| 关 键 词： | 南北地震带北段 地震层析成像 地壳速度结构 低速层 青藏高原东北缘 |
| 收稿时间： | 2018-01-05 |
Crustal velocity structure beneath the northern North-South Seismic Zone from local seismic tomography and its tectonic implications |
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| Affiliation: | 1.Institute of Geophysics，China Earthquake Administration，Beijing 100081，China2.Key Laboratory of Seismic Observation and Geophysical Imaging，China Earthquake Administration，Beijing 100081，China |
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| Abstract: | We collected and picked the first arrivals of P and S waves of local and regional events recorded by 680 portable broadband seismic stations of the ChinArray-Himalaya Ⅱ and 217 fixed stations of the Chinese Seismic Network located on the northern North-South Seismic Zone （96°E?110°E, 30°N?44°N）. We got a 3D P and S wave velocity （vP and vS） structure of the crust beneath the northern North-South Seismic Zone with a horizontal grid space of 0.33°×0.33° by tomography. The tomography results reveal obvious integrated low velocity anomalies at 30 km depth beneath the northeastern Tibetan Plateau. The low velocity zone extends southward to the Longmenshan fault and extends eastward to the 106°E, dividing the Qinling orogenic belt into low velocity zone at westside and high velocity zone at eastside. The low velocity zone also extends northeast along the Yinchuan-Hetao graben, and extends northward through the Hexi Corridor, and it shows low velocity anomalies beneath the Alxa block at 30 km depth. This implicates that the extension of the Tibetan Plateau may be blocked by the relatively strong Sichuan basin and Qinling block in the east, while the extension affects the Hexi Corridor and the Alashan block, as well as the northwestern margin of Ordos along the Yinchuan-Hetao graben. At 50 km depth, it shows high velocity anomalies beneath the Alxa block and eastern Qilian orogenic belt, indicating possible southward subduction of the Alxa block beneath the eastern Qilian orogenic belt. Most crustal earthquakes in the studied region generally occurred along the fault zones between low velocity and high velocity zones where vP and vS change drastically over a short distance. The projections of large earthquakes （M≥6.0） at 30 km depth are almost located in the low velocity zone, which may indicate that the background of strong earthquakes is related to the low velocity zone beneath the source area. |
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