张北6.2级地震的连续形变前兆异常时空特征

采用首都圈连续形变观测网内倾斜及应变的观测资料,对张北地震的前兆异常及其特征进行了分析研究,得到如下结果:震前1年半到两年(即1996年)在这一地区存在较大区域的连续形变异常;在这种中长异常背景的基础上,倾斜、应变观测结果再次出现新一轮异常,并且新的异常在观测地点和时间上一致,异常点相对于中长期时的空间范围缩小,向震中区集中(约200 km范围内).新一轮异常从其中最早的异常开始到地震发生在1年以内,并且随发震时间的逼近,不同观测项目和不同观测方向的各种参量的异常表现更为一致和显著,其中以离震中最近的张家口的异常变化最为突出.

THE ABNORMAL VARIETY CHARACTERISTIC OF THE EARTH TIDE OBSERVATION AND PRECURSOR OF THE ZHANGBEI EARTHQUAKE (Ms6.2)

The precursory anomalies and its characteristics of the Zhangbei earthquake are analyzed and researched using the observed data of the tilt and strain tides in the capital area. The results show that from one year and half to two years before the earthquake, there were widely anomalies of the deformalion in the area. On the basis of the background of the long-mid anomalies, a new round of anomalies were observed again. These new ones were coincident in place and starting time, and the abnormal points were reduced and concentrated into the epicenter (in a ramge of about 200 km). The duration of the new round of abnormalities was less than 1 year before the earthquake, the anomalies of various parameters in different observation items and different directions were more consistent and obvious when the earthquake approaching. The abnormal changes of observation at Zhangjakou which is nearest to the epicenter were the biggest.