繁峙-太仆寺旗剖面 S 波资料解释及深部构造特征与地震相关性分析

Interpretation of S wave Data from Fanshi Taipusiqi DSS Profile and Analysis of Correlation between Deep Structural Characteristics and Seismicity

通过对繁峙－怀安－太仆寺旗三分向深地震测深宽角反射＼折射剖面的Ｓ波资料进行处理，结合Ｐ波处理结果，给出了地壳上地幔的Ｓ波速度ＶＳ及介质物性参数泊松比σ的二维结构；综合地质及其它地球物理资料，参照国内外岩石物理参数的实验结果，对地壳深部结构、构造及岩性进行了解释和推测。其结论为：中上地壳大部分地区σ值不大于０２５，岩石主要由花岗岩组成，整体呈脆性；其中阳原－怀安间的上地壳下层岩体，含有来自上地幔的无机ＣＯ２气体并还原释放出碳；下地壳及壳幔过渡层σ值大部分大于０２６，整体呈相对塑性；下地壳岩性在怀安以北地区为中酸性麻粒岩、怀安至阳原为英角闪片麻岩、阳原以南为石英岩；莫霍＼过渡层主要由剖面两端的基性麻粒岩－闪岩和剖面中部地区的石英云母片岩－中性麻粒岩所组成。根据σ值的横向变化并结合震相特征，推断了阳原及张北附近的超壳断裂带和怀安的深断裂带。结合地震活动性，对地震较为集中发生的阳原上地壳下层进行了解释，认定是由于该岩体较脆硬且“漂浮”在下部的较塑性岩体之上，受超壳断裂带、区域应力场及上地幔物质上涌的影响，岩体容易在σ值显著变化的部位产生错动、滑动，引发地震，且地震多集中于σ值较小的脆硬岩体一侧。

By processing S wave data from Fanshi Huai′an Taipusiqi DSS profile,which is a three component wide angle reflection/refraction profile,and in the light of the results from P wave interpretation,2 D structures of the crust and upper mantle are presented,including S wave velocity V S and the physical parameter of medium Poissn′s ratio σ .Taking other geological and geophysical information into account,and with reference to the results from petrophysical experiments at home and abroad,we carried out interpretation and inference with respect to deep crustal structure,tectonics and lithologic character.It has been concluded that:in the upper and middle crust, σ values are mostly not greater than 0 25, and rocks,which generally assume brittle,are mainly composed of granite,rocks in the lower layer of upper crust between Yangyuan Huai′an contain inorganic CO 2 which itself releases carbon;In the lower crust and crust mantle transitional zone,which is comparatively plastic, σ values are mostly greater than 0 26,rocks in the lower crust are intermediate acidity granulite north of Huai′an,quartzic amphibole gneiss between Huai′an Yangyuan,and quartzite south of Yanyuan;M discontinuity is mainly composed of basic granulite amphibolite at both ends of the profile and quartzmica gneiss intermediate granulite in the middle area of the profile. On the basis of lateral variation in σ values,taking seismic phase characteristics into consideration,the ultra crustal fault near Yangyuan and Zhangbei and the abyssal fault at Huai′an are deduced.Taking seismicity into account,we interprete the lower layer of the upper crust under Yangyuan which is an earthquake prone area,and believe that the rock mass here is comaratively brittle and hard and “floats” over the compartively plastic rock mass under it;Affected by the ultra crustal fault regional stress field and the upwelling of material from upper mantle,dislocation and slide may take place in the rock mass where σ values vary obviously,thus,triggering earthquakes which tend to center on the trittle and hard side of the rock mass with low σ values.