新构造运动背景下天津中部地区活动断裂浅层地震勘探及新认识

天津地处渤海湾盆地北西西向北京-蓬莱断裂带与北东向唐山-河间-磁县新生断裂带交汇部位,盆地内沉积盖层(N1-2-Q)覆盖较厚,新构造运动频繁,为了进一步揭示活动断裂浅部特征,本文利用浅层地震勘探方法查明了天津中部地区部分断裂(杨柳青断裂、杨村断裂)新构造运动背景下的表现形式及展布特征.结果表明,杨柳青断裂(FP3、FP6)在新构造运动时期仍继续活动,形成截切主断裂而反向复活的继续活动断裂(FP4、FP5),且为第四纪活动断裂;杨村断裂(FP2)于新构造运动时期在主断裂上直接复活,为第四纪活动断裂;同时识别出多条发育于新近系明化镇-第四系(N1-2-Q)沉积盖层中的新生断裂(FP1,FP7~FP10).新构造运动背景下天津中部地区活动断裂发育,既有继承性活动的继续活动断裂,也有具盖层断裂特征的新生断裂.

Shallow seismic exploration and new understanding of active faults in central tianjin under the background of neotectonic movement

Tianjin is located at the intersection of northwest beijingpenglai fault zone and northeast tangshan hejian-cixian cenozoic fault zone in bohai bay basin.The sedimentary cover(N1-2-Q)in the basin is thick and neotectonic movements are frequent.Shallow seismic exploration method is the main method to detect concealed active faults in the overlying area at present.No need for surface drilling,non-destructive detection,high precision,but at the same time in the city can not use explosive source,the construction cost is high.In order to further reveal the characteristics of the shallow active faults in central tianjin under the background of neotectonic movement,some active faults in wuqing-panzhuang area were taken as research objects.Through comprehensive analysis of the previous gravimetric results and geological data,three shallow seismic exploration lines were laid.In order to ensure that the detection results could reveal the geological structure characteristics of greater depth and higher resolution,the observation system used unilateral vibroseis excitation,and large receiving array,and the full coverage times adopted more than 37 times,and obtained reliable original data.Through fine data processing,high quality detection results have been obtained.The distribution of faults(Yangliuqing fault and Yangcun fault)in the central area of tianjin under the background of neotectonic movement have been ascertained.The results show that the Yangliuqing fault(FP3、FP6)continues to be active during the neotectonic movement period.Continuous active faults(FP4,FP5)intercept the main fault and resurrect reversely.The Yangcun fault(FP2)was revived directly along the main fault during the neotectonic movement period.The Yangliuqing fault and Yangcun fault are quaternary active faults.Additionally,several newly formed faults(FP1,FP7~FP10)were also identified in this study,which strictly developed in the Neogene Minghuaten-Quaternary(N1-2-Q)sedimentary cover.So it can be concluded that active faults developed in the middle of tianjin under the background of neotectonic movement.There are both continuous-active faults with inheritable activities and new-born faults with the characteristics of caprock faults.