利用宽角反射/折射和深反射探测剖面揭示三河-平谷大震区深部结构特征

利用三河—平谷8.0级大震区实施的深地震反射剖面与宽角反射剖面探测方法获得的结果进行了综合研究和解释. 结果表明：两种探测方法给出的地壳基本分层是一致的，在三河—平谷大震区上地壳的埋深为21～23km，莫霍界面的深度为36～37km；该地区基底结构起伏变化较大，浅部断裂发育，在确定的数条断裂构造带中夏垫断裂是一条特征明显、深浅共存的断裂构造带；震源区周围差异明显的速度异常结构和特殊而复杂的地质构造环境意味着这些部位是发生大地震的有利部位；该地区莫霍界面起伏变化和较厚的反射叠层以及局部复杂的楔形反射带的存在等现象表明，该地区地壳结构发生过强烈的挤压、变形，同时也反映出岩浆活动对下地壳结构进行了物质的和结构的强烈改造，从而构成了该地区复杂的地壳深部结构，可将其视为三河—平谷8.0级大地震孕育和发生的深部要素.

DEEP STRUCTURAL FEATURES OF THE SANHE-PINGGU GREAT EARTHQUAKE AREA IMAGED BY WIDE-ANGLE AND DEEP SEISMIC REFLECTION PROFILING

In this paper, the data from deep seismic reflection and wide angle reflection profiling completed in the Sanhe—Pinggu great earthquake (M=8.0) area are comprehensively studied and interpreted. The results shows that the layered crustal structures obtained by the two investigation methods are basically consistent. In the Sanhe—Pinggu earthquake area, where the fluctuation and variation of basement structures are conside rable and shallow faults well developed, the thickness of the upper crust and the depth of Moho interface are 21～23km and 36～37km, respectively. Among several fault zones determined by this study, the Xiadian fault is a tectonic zone with obvious characteristics and coexistence of both shallow and deep faults. Surrounding the focus, anomalous velocity structures which exhibit apparent differences along with special and complex geological tectonic environment mean that these parts are favora ble for earthquake occurrence. The phenomena of Moho interface fl uctuation and rather thick overlapping reflection layers and existence of locall y complex cuneiform reflection zones and so on, indicate that the strong compression and deformation of the crustal structures had taken place in this region, and magmatic activity caused strong reformation of materials and st ructures in lower crust, further more resulted in complicated deep crustal struc tures in the area and maybe regarded as the deep background for the development and occurrence of Sanhe—Pinggu M8 earthquake.