古雷—石城地区地壳与上地幔地震波速度结构及莫霍面特征

CHARACTERISTICS OF SEISMIC VELOCITY STRUCTURE OF THE CRUST AND UPPER MANTLE AND MOHO DISCONTINUITY IN GULEI-SHICHENG AREA

本文是1986年古雷—石城剖面及嵩口—宜城剖面深地震测深资料的初步研究结果。 对古雷—石城的纵剖面资料,分析了震相特征,共识别出五个波组:P_2、P_3~0、P_4~0、P_5~0及P_n(P_n^0)。通过对波的走时反演,正演拟合和理论地震图方法等计算,得到了该区地壳与上地幔结构模型。 古雷—石城地区地壳具有多层结构,并可划分为上、中、下三层。古雷炮点给出的厚度分别为1.0km、15.7km、12.8km,地壳平均速度为6.29km/s,深度为29.5km,上地幔顶面P_n波速度为7.83km/s。石城炮点给出厚度分别为1.8km、18.3km、12.4km。地壳平均速度为6.29km/3,深度为32.4km,土地幔顶面P_n速度为8.00km/s。 在中地壳下部存在一低速层,其厚度为2.8km,速度为5.85km/s。根据其它研究结果,初步判断低速层介质是半熔融物质组成。 测区内横向变化比较强烈。从东向西有长乐—诏安、政和—海丰和邵武—河源三个大断裂穿过该区,并且都深切至莫霍面;在漳州盆地之下莫霍面隆起约3km,戴云山区下莫霍面凹陷近2km;永安—梅州莫霍面隆起接近3km。莫霍面分布显示出从东南向西北逐渐加深。 宜城—连城—嵩口非纵剖面显示了莫霍面在两处有明显断错,错距约2km邵。表明昭武—河源断裂是切割莫霍面的深大断裂。

This paper describes the result of preliminary study on the deep seismic sounding data along the Gulei-Shicheng profile and the Songkou - Yicheng profile. After analysis the phase characteristics in the data along the Gulei -Shicheng profile, five waves are distinguished, namely, P6, P3, P4, P5 and Pn (Pno) . After calculation of wave traveltime by inversion, direct fitting and on theoretical seismogram, a structural model of upper mantle in the area is constructed. The structure of the crust in Gulei-Shicheng area is multilayer. It can be distinguished into three layers , the upper , middle and lower. Their thichness under the Gulei shot point is 1. 0 km, 15. 7km and 12. 8 km , respectively. The average velocity of the crust is 6. 29 km/s, the depth is 29. 5 km, Pn wave velocity of the top surface of upper mantle is 7. 83 km/s. The thichness under the Shicheng shot point is 1. 8 km, 18. 3 km and 12. 4 km , respectively. The average velocity of the crust is 6. 29 m/s, the depth is 32. 4 km and Pn wave velocity of the top surface of upper mantle is 8. 00 km/s. According to other results, we infer preliminarily that a low-velocity zone composed of semi -molten materials exists in the lower part of the middle crust. In the studied area the lateral variation in velocity is stronger. Three major faults. Changle-Zhaoan. Zhenghe-Haifeng and Shaowu-Heyuan faults from east to west, pass through this area and cut deeply down to the Moho discontinuity. Moho discontinuity swells up 3. 0 beneath the Zhangzhou basin, depresses near 2. 0 in the Daiyunshan area ; and again swells up nearly 3 km in Yongan - MeiZhou area. The depth of Moho discontinuity gradually increases from southeast to northwest. Along the non-longitudinal Yicheng-Liancheng-Songkou profile, the Moho discontinuity is obviously offset at two sites with amplitude about 2. 0 km. It indicates that the Shaowu-Heyuan fault is a deep fault cutting the Moho discintinuity.