中文摘要：

2006年7月4日河北省文安县发生的5．1级地震是1998年1月10日张北6．2级地震后首都圈内最大的一次地震。该震震中烈度偏低，而远在100km以外的北京等地区却出现较高的烈度异常。本文根据首都圈数字强震台网及其烈度速报系统测定的地震动强度等值线图，对该地震的烈度异常情况进行了分析，并对首都圈内3个烈度异常区的成因进行了初步的分析。结合震源的发震机理、地质结构和地震波射线路径等，分析了造成该次地震震中低烈度、小灾情，而外围烈度较高的基本因素。

英文摘要：

An earthquake measuring M5.1 on the Richter scale has struck Wen＇an County, Hebei Province on July 4, 2006. No casualties have been reported, there was just slight damage. The disaster conditions of this time is the lightest on the record tally from 4.9 - 5.1 since the CCDSN （China Center of Digital Seismic Network） was build in 1999. The epicenter intensity of this earthquake was not strong, while in areas like Beijing which is 100km far away, there appeared abnormal high intensity. This article discusses the reasons behind this strange phenomenon, with the diagrams of intensity isolines drawn by the Capital Zone Strong Motion Observation Center as reference, as well as the mechanism of earthshaking in the epicenter, and the seismic histories, geological structure and ways of spreading of the seismic waves in areas 150 km around the epicenter. And it is concluded that the special dynamic and geological situations were the main causes of the strange phenomenon of low intensity degree in epicenter, slight damages, yet high intensity in the surrounding areas.