华东中强震的构造分类及地震活动图像中、短期异常特征

Structure classification of moderately strong earthquakes in East China and the characteristics of medium-and short-term anomalies of seismicity pattern

基于在相似外加载荷作用下结构相似的构造可表现出类似的破裂图像及前兆演化特征的实验室研究结果,对华东地区现代中强地震进行了初步构造分类,在此基础上分析研究了19次震例前地震活动图像异常的统计特征。结果表明:①大多数震例前具有2～3年尺度的地震学异常,图像以"条带"和"增强"为主;②多数地震在条带异常后有1～2年的中期平静,震前0.5～1年左右在中期平静背景上出现"集中、收缩"图像;③震前3个月左右的较短时间内,多数震例震中附近以短期"平静"为主;④部分震例前短时间内震中附近有"显著性地震"事件发生;⑤不同构造类型震例前,地震异常图像可能存在差异;⑥华东地区中强地震可能更多是属于沿原存断裂继承性破裂导致的地震,震源力学性质多为拉张型。拉张与挤压型地震的异常特点也可能存在差异。但由于震例较少,其确定性和成因还需进一步探讨。

The current moderately strong earthquakes in East China have been preliminarily classified according to the tectonics based on information from laboratory study results-it presents the similar fracture pattern and characteristics of precursory evolution to similar structural tectonics on the action of extra adding loads. Furthermore, we have analyzed and studied the seismicity patterns and some general and specific characteristics of seismic pattern before 19 earthquakes. The results show some features as follows: ① Most cases have medium-term seismological anomaly of 2 years, being mainly seismic band and enhancement of patterns; ② Medium-short term of 1 year calm occurs after the emerging of seismic bands, and then the concentrated or contracted patterns of 0.5 year before the earthquakes; ③ In most cases, there is principally seismic quiescence around epicenter about a short period of 3 to 6 months before the earthquakes; ④ Partly, for a short time before the earthquakes, significance seismic events occurred near the epicenter region; ⑤ Seismic anomaly patterns might be different before various tectonic types of earthquakes; ⑥ Moderately strong earthquakes occurred in East China are mostly dislocation slip type of earthquakes that its fracture along with pre-existing faults, and the focal mechanical behavior mainly belong to stretch type, the anomaly characteristics of stretch and compression type probably have some differences. Nevertheless, it's necessary to discuss further the cause and definition because of insufficiency of earthquake examples.