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1998年 1月 1 0日在河北省张北县和尚义县之间 (41°0 6′N,1 1 4°1 8′E)发生 6.2级地震 ,震源深度为 1 0 km。震前一二年发现有明显的地震前兆异常 :4级地震条带明显 ,区域地震活动增强并出现低 b值异常等 ;震前数天至数月有赤城、张家口地倾斜异常 ,阳原、宝昌地电阻率异常 ,延庆地下水位异常 ,呼和浩特、北京地磁 ,地磁低点位移以及热红外等前兆异常。中、短期地震前兆较丰富 ,临震前兆异常不够明显。1 997、1 998年初北京西北至晋、冀、内蒙古交界地区被列为可能发生 5～ 6级地震重点危险区。张北 6.2级地震虽然有较好的年度中期预报 ,但没有作出临震 (几天内 )预报
On January 10, 1998, a magnitude 6.2 earthquake occurred between Zhangbei County and Shangyi County of Hebei Province (41 ° 0 6’N, 114 ° 180’E) with a focal depth of 10 km. A significant earthquake precursory anomaly was found in one or two years before the earthquake: obvious bands of magnitude 4 earthquakes, enhanced regional seismicity and low b-value anomalies, etc. There were anomalies in Chicheng and Zhangjiakou days before the earthquake, Baochang resistivity anomalies, Yanqing groundwater anomalies, Hohhot, Beijing geomagnetism, geomagnetic low displacement and thermal infrared precursory anomalies. Medium and short-term earthquake precursors are abundant, and precursory anomalies are not obvious enough. 1 997,1 At the beginning of 1998, the area from the northwest of Beijing to Jin, Ji and Inner Mongolia was listed as the key danger area of 5-6 earthquakes that may occur. Despite the good annual medium-term forecast, the 6.2-magnitude Zhangbei earthquake did not make a temporary earthquake (within a few days) forecast