2013年通辽MS5.3地震及其前震序列判定

The Tongliao MS5． 3 earthquake and its foreshock determination

摘要:

以2013年4月22日内蒙古通辽MS5.3地震为研究对象，在序列统计分析的基础上，通过HypoDD双差定位和震源机制求解，分析了之前的ML4.4地震与MS5.3地震的关系。结果表明，通辽MS5.3地震是在震中区中小地震长期平静和震前短期活动增强的背景下发生的一次中强地震;地震精确定位结果显示，通辽MS5.3地震序列整体呈NW向展布，延伸约10km，ML≥3.0余震集中发生于主震南侧约2km处;MS5.3主震和ML4.4前震的震中相距约1.8km，震源深度分别为7.208、7.089km，表明两者的震源位置比较接近，可能发生于同一断层面;震源机制结果表明，通辽MS5.3主震的震源机制为走滑型，余震震源机制类型比较凌乱，由前期的走滑为主转变为后期的正断层和逆冲型;3次较大前震的震源机制解具有一致性，均为正断层，一定程度上表现了震中区地壳介质在宏观破裂前存在明显的各向异性，具体表现为裂隙的定向排列，这种“一致性”的震兆状态在应力的进一步作用下孕育发生了主震。根据地震序列的时空分布特点和震源机制相似性，综合判定通辽MS5.3地震应为前震-主震-余震型。

Abstract:

The paper took the 2013 Tongliao MS5. 3 earthquake as the research object and analyzed and discussed the relationship between ML4. 4 an MS5. 3 earthquakes on basis of statistical analysis of earthquake sequence and HypoDD location and focal mechanism solutions． The results showed that，the Tongliao MS5. 3 earthquake occurred with the background of longterm quiescence of medium-small earthquakes and short-term enhancement activity in epicentral area． The results of accurate seismic location showed that the Tongliao MS5． 3 earthquake sequence distributes on the NW trending，with an extension of 10km． ML ≥3. 0 aftershocks concentration occurred southern of main shock． The distance between MS5. 3 and ML4. 4 earthquakes is about 1. 8km with focal depths of 7． 208km and 7． 089km，respectively． Their focal location is very close and they might have occurred on the same fault plane． The results of focal mechanism showed that the Tongliao MS5. 3 earthquake was of a strike-slip type． Focal mechanism of aftershocks were in disorder with time lapse． The type changed from strike-slip to thrust and normal fault． The bigger foreshocks had similar focal mechanism． They were all normal fault，and to some extent exhibited a obvious crustal medium anisotropy in epicentral area before macroscopic fracture． The fracture was directional alignment with stress action enhanced，and the “consistency” of seismic precursor state would gestate the main shock． According to the characteristics of temporal-spatial distribution of earthquake sequence and similarity of focal mechanism，we judge that the Tongliao MS5. 3 earthquake is a foreshock-mainshock-aftershock type．