2013年通辽5.3级地震及余震的破裂特征讨论

DISCUSSION ON RUPTURE CHARACTERISTICS OF THE 2013 TONGLIAO M5.3 EARTHQUAKE AND ITS AFTERSHOCKS

对比使用了2种速度模型,采用Hypo DD方法对通辽5.3级地震序列进行了精确定位,采用CAP方法反演了5.3级地震的震源机制解,利用精确定位后的小震分布和区域应力场定量拟合了发震断层面参数,综合判定了通辽5.3级地震的断层面几何形态、破裂特征及可能的发震构造。Hypo DD定位结果显示,通辽5.3级地震的位置为42.95°N,122.37°E,序列整体呈NW向展布,早期余震分散分布于NW方向,晚期余震则集中分布于NEE方向;随着时间推移,余震活动逐渐向地壳浅部扩展。通过与主震的震源机制解对比分析,认为以NNW向余震分布进行断层拟合的结果比较符合主震的断层面破裂特征;即通辽5.3级主震的发震断层面的空间顶点坐标为左上角(43.00°N,122.35°E;深度3.3km)、左下角(43.00°N,122.35°E;深度8.9km)、右上角(42.92°N,122.37°E;深度8.9km)、右下角(42.92°N,122.37°E;深度3.3km)。按照假定的矩形进行断层形状规划,则通辽5.3级主震断层面的扩展范围为5.6km×9.0km,断层面走向349°(NNW向)、倾角86°、滑动角15°,断层面错动类型为左旋走滑型;由此推断主震破裂的整体过程自震源处向断层的NW和SE两侧剪切破裂,东南侧破裂程度较大,晚期破裂集中于此但破裂未及地表。

On two velocity models,the Hypo DD method is used to accurately locate the Tongliao M5. 3 earthquake sequence,then the CAP method is used to invert the focal mechanism solutions. The parameters of the seismogenic fault plane are fitted quantitatively by the small earthquake distribution and the regional stress field. The geometry,rupture features and possible seismogenic structure of the Tongliao M5. 3 earthquake are comprehensively determined. The Hypo DD relocation results show that this earthquake is located at 42. 95° N,122. 37° E,the whole sequence trends in NW and major aftershocks（ ML≥3. 0） strike in NEE direction. With the time elapsed,the aftershocks extended to the shallow crust gradually. Comparing the focal mechanism solutions and relocation results,we determine that the fitted causative fault based on NNW-trending aftershock distribution is reliable,which has the top left corner（ 43. 00°N,122. 35°E,depth 3. 3 km）,lower left corner（ 43. 00°N,122. 35°E,depth8. 9 km）,upper right corner（ 42. 92° N,122. 37° E,depth 3. 3 km）,lower right corner（ 42. 92° N,122. 37°E,depth 8. 9 km）,extending range 3 km × 7 km,trending in 349°（ NNW）,dip angle 86°（ nearly vertical）,and slip angle 15°. It is inferred that whole process of main shock rupture is from the source to the NW and SE sides as a shear. The rupture degree is larger in southeast where the late rupture concentrated,and did not reach the surface.