| 三峡库区上地壳S波衰减成像研究 |
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| 引用本文： | 吴海波,王杰,杜承宸,申学林,陈俊华.三峡库区上地壳S波衰减成像研究[J].地震学报,2016,38(2):188-198. |
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| 作者姓名： | 吴海波 王杰 杜承宸 申学林 陈俊华 |
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| 作者单位： | 1.中国武汉 430071 中国地震局地震研究所(地震大地测量重点实验室) |
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| 基金项目： | 中国地震局测震台网青年骨干培养专项20150418中国地震局地震科技星火计划项目XH14035YSX |
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| 摘 要： | 利用三峡数字地震台网2009年1月—2015年2月记录的1300多次ML>1.5小震事件6000多条射线的S波数据， 利用S波衰减层析成像技术获得了三峡库区秭归—巴东段上地壳QS成像分布图． 结果显示， 三峡库区上地壳QS值存在明显的横向不均匀性， 沿水库近岸区主要为QS高值区， 外围NE， NW， SW和SE 等4个方向上均存在QS低值异常区， 这是由于这些异常区位于不同地层转换带， 岩层较易破碎， 易于库水渗流所致． 在巫山—秭归段剖面上， 本文QS成像结果与人工地震测深剖面上基底至上地壳底部之间岩层的Q值变化形态基本一致， 前者均值比后者低， 反映了上地壳深部介质对地震波衰减特性的影响． 2013年巴东MS5.1震群活动和2014年秭归MS4.5， MS4.7震群活动均分布在QS高值与低值过渡区， 这种区域的地下介质位于“软”、 “硬”转换带上， 岩层易破碎， 应力和能量易集聚， Q值易受水的渗透引起变化， 从而降低发震断层抗剪切强度而诱发地震．
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| 关 键 词： | Q值 衰减系数 QS值成像 人工测深剖面 |
| 收稿时间： | 2015-08-17 |
Tomography of the S wave attenuation in the upper crust of Three Gorges Reservoir region |
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| Institution: | 1.Key Laboratory of Earthquake Geodesy, Institute of Seismology, China Earthquake Administration, Wuhan 430071, China2.Earthquake Administration of Hubei Province, Wuhan 430071, China |
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| Abstract: | A 2-D S-wave QS values of the upper crust of Zigui-Badong segment beneath the Three Gorges Reservoir region are estimated by means of S wave attenuation tomography based on more than 6000 S wave-rays of 1300 small seismic events with ML>1.5 recorded by digital seismic network of Three Gorges from January 2009 to February 2015. The results show that QS exhibits a significantly lateral heterogeneity distribution in Three Gorges Reservoir region, with high QS value mainly in the nearby riversides and low QS value in the surrounding area in the northeast, northwest, southwest and southeast directions. Particularly, the low QS value is closely related to seepage of reservoir water due to the conversion and fragment of rock stratum. The variation of QS value in this paper is in accord with Q value of rock stratum from rock-basement to the bottom of the upper crust from the Wushan-Zigui deep seismic sounding (DSS) profile, which reflects that the deep media of upper crust have influence on the seismic wave attenuation. The MS5.1 Badong earthquake swarm in 2013 and the MS4.5, MS4.7 Zigui earthquake swarms in 2014 were basically converged to transitional edge regions of high and low QS values. That is because that, the physical property of the crustal medium is located on the weak-soft transitional region, strain energy is prone to accumulate, and QS value also decreses due to the permeation of the water, furthermore, the shear strength of the seismogenic fault is reduced so as to induce earthquakes. |
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