四川松潘—平武地震前后的地壳垂直形变

VERTICAL GROUND SURFACE DEFORMATION BEFORE AND AFTER THE 1976 SONGPAN-PINGWU EARTHQUAKE

  • 摘要: 松潘—平武地震前后的地壳形变资料表明, 在震中周围地形变具有规律性变化.1975年7—9月第一次复测, 发现1960年以来岷江断裂两盘存在年速率约3毫米的缓慢相对运动;1975年底再次复测, 证明东盘加速上升.当临近震前2—3月时, 一些构造敏感点附近出现短期形变异常.与此同时, 松潘川主寺短水准亦呈短期异常.震后漳腊盆地相对下沉, 较场迭溪弧形构造南侧相对抬升, 南坪西侧余震延伸方向上形变则呈弹性恢复, 从震源外围反映了地震的孕育释放过程.文中还通过地形变与地震要素的探讨, 初步建立了用垂直形变量估算震级的关系式.计算结果符合实际, 说明用于中长期预报具有一定意义.

     

    Abstract: Before and after the Songpan—Pingwu earthquake of 1976, results of repeated geodetic surveys show certain regularities in ground surface deformation around the epicentral area. The first survey carried out in July—September of 1975, indicated a slow vertical relative displacement of rate 3mm/year on both sides of the Minjiang fault, since 1960. In 1975, another survey revealed accelerated rise of the east side of the same fault and 2—3 months preceding the earthquake, anomalous ground surface deformation took place near certain sensitive points of some tectonic structure. At the same time, the result of repeated surveys of a short base-line, laid at Songpan also gave short-range anomalies.After the earthquake, the Zhangla Basin descended relative to the surroundings, while the area south of the Jiaochang Diexi arc structure uplifted. West of Nanping, along the extension of the aftershock belt, vertical surface deformation seems to show elastic recovery of the crust. Deformations in the regions around the epicenter, reflected the stages of the process of development and energy release of the earthquake.Based on certain discussions on the connection between crustal deformation and earthquake parameters, a preliminary relationship of vertical ground surface deformation and earthquake magnitudes has been established. Some numerical computations gave no conflicting results which perhaps suggest certain usefulness.

     

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