Characteristics of Fault Structure in Tianjin Area

Having processed and interpreted some gravity data,we have understood,to a certain degree,of the fault structures in Tianjin area.Fault Ⅰ and Ⅱ are the master faults in the area,they are large in scale,good in controlling,and long period of time in inherited activity.In addition,they are mainly the boundary lines for different kinds of structural zones or divide this area into sub-structural units.So these faults play an important controlling role for the formation,development,and evolution.Most of the faults are characterized by stages/phases and long-term inherited activity,although the activity is different in different development period or in the same period,forming a fault system mainly composed by large-scale faults.Horizont ally,this structural frame is mainly the NE,NW,and Nearly EW directions,with the SN being the secondary.At the same time,we infer that the Ⅰ,Ⅱ grade fractures were formedduring the earlier time,mostly Paleozoic,Mesozoic generation and that the majority of fracture after the formation of the transformation of repeated tectonic movements have repeatedly rise and the charact eristics of long-ter mactivities.Ⅲ,Ⅳ-level of fault were formed later,mostly in the Paleogene and is characterized by intense activity,with the Paleogene period being the intense activity.