澜沧地震前昆明弥渡重力场变化特征

CHARACTERISTICS OF GRAVITATIONAL FIELD VARIATIONSIN KUNMING AND MIDU AREAS PRIOR TO THELANCANG EARTHQUAKE

本文用澜沧—耿马地震前后昆明台和弥渡台的重力固体潮观测资料对震前昆明、弥渡的重力场进行了潮汐变化和非潮汐变化的分析研究。研究表明澜沧—耿马地震前昆明、弥渡的重力场变化有如下特征:1.重力值变化和重力值差分值变化不明显。2.重力潮汐因子有较明显的负异常变化。3.重力潮汐因子变化的异常时间和1976年5月29日龙陵7.3、7.4级地震异常时间半年多接近;异常的最大变幅处于同一量级,但澜沧地震前昆明台的最大变幅4.7%比龙陵地震前的最大变幅3.4%稍大。4.重力潮汐因子变化有较明显的中期异常,短期异常也有一定反映,但临震异常不明显。

Using observational data of gravitational earth tidela registered at Kunming and Midu stations prior to and after the Lancang-Gengma earthquake, this paper analyses and studies the tidal and non-tidal variations of the gravitational field in Kunming and Midu areas prior to that earthquake. The study throws light on the following features of gravitational field variations prior to the La-ncang-Genma earthquake in Kunming and Midu.1. Variations of gravitational values and the differential gravitational values were not obvious;2. Fairly evident negative changes in gravitationnl tidal factor did occur;3. The duration of anomalies in gravitational tidal factor lasted more than half a year which nearly coincided with the preshock anomalies occurred before the M 7.3 and M 7.4 Longling earthquake occurred on May 29, 1976. The maximum variation amplitude of the anomalies fell in the same magnitude, yet the maximum variation amplitude reached 4.7% at Kunming station before the Lancang earthquake which was slightly greater than 3.4% variation registered before the Longling earthquake.4. Evident mid-time anomalies of gravitational tidal factor were observed, whereas there were certain indications of short-time anomalies nevertheless, no observable anomalies were detected immediately before the earthquake.