1985～2003京津唐张地区重力变化

Gravity variation in the Beijing-Tianjin-Tangshan-Zhangjiakou region during the period of 1985～2003

本文分析了京津唐张地区1985～2003年详实的重复重力测量资料，重力变化的图像显示该地区的重力变化具有明显的区域性特征；最为显著的变化是测网南部地区出现的较大范围重力增加，增加幅值在(100～300)×10^(-8)m·s^(-2)之间，从可搜集到的高程及地下水资料分析，造成这一变化的主要原因是该地区大量开采地下流体而引起的大面积地面沉降；测网北部山区重力趋势性减小，19年减小幅值约30×10^(-87)m·s^(-2)，与香山绝对重力点的变化量相当，高程及地下水对此种趋势的影响不大，大面积山区继承性、同步性的构造运动可能是造成地表重力趋势性变化的主要原因；而东部地区重力变化的明显特征是1990年6月至1994年6月间有一重力的快速下降然后上升过程，这可能是与1995年10月滦县 M 5.9地震有关的重力变化．相比之下地下水位的变化对重力趋势的影响较微弱．

Repetitive gravity observation data with high resolution in the Beijing-Tianjin-Tangshan-Zhangjiakou(BT-TZ)region during 1985～2003 is analyzed and the features of gravity variations typifying the regional characteristicsare obtained.The most obvious feature is the increase of gravity value with an increment of(100～300)×10^(-8)m·s^(-2) appearing in the southern plain area.According to the data of elevation and underground water tables,the incre-ment may result from the ground subsidence in a vast area induced by serious fluid withdrawal.On the other hand,gravity drop tendency is shown in the northern mountain area with a total decrease of about 30×10^(-8)m·s^(-2) in theperiod of 19 years,which corresponds with the gravity decrease at Xiangshan station located at the edge of mountainarea,where 2 or 3 times of absolute gravity measure are carried out every year.According to the study,deep-site tec-tonic movement may be the main cause of the gravity variation trend in the north,and elevation variations and the wa-ter table fluctuations may not have much influence on the trend.In the eastern region,gravity variations in a large ar-ea undergo an increasing process after a rapid decreasing stage during the period of June 1990 to June 1994,whichmay be related to Luanxian M5.9 earthquake in Oct.1995.The effect of the water table variation on the gravity vari-ation is relatively small.