基于重复微震的小江断裂带深部滑动速率研究

利用云南数字地震台网1999~2011年的波形资料,通过辨识源于同一位置破裂的重复微震来估算小江断裂带不同段落、不同深度的断层滑动速率.针对研究区台站分布稀疏的客观情况,应用了在子采样条件下基于S-P相对到时差来约束地震相对位置的方法,在小江断裂带识别出29组重复微震,其复发间隔存在差异变化.重复微震的时空分布初步分析表明:准周期的重复微震在空间上相对独立,远离其它重复微震和背景地震; 在重复微震集中分布的区域,位置相近的重复微震可能会相互作用而影响其复发间隔;在背景地震活跃阶段,相邻背景地震发生引起的应力变化可能缩短重复微震的复发间隔.利用重复微震的地震矩和重复间隔,估算出小江断裂带孕震深处3~12 km的滑动速率为1.6~10.1 mm·a-1,显示不同破裂段的深部滑动速率存在明显差异.

Estimates of deep slip rate along the Xiaojiang fault with repeating microearthquake data

Deep slip rates at different segments of the Xiaojiang fault zone were estimated using repeating microearthquakes between 1999 and 2011 recorded by the Yunnan Digital Seismic Network. Due to the sparsity of the network in the study area, we used an empirical method to constrain the relative distance between event pairs based on S-P differential times measured at subsample accuracy. We used this method to identify a total of 29 sequences of repeating microearthquakes along the Xiaojiang fault zone,which show substantial variations in the recurrence intervals. Based on the spatial-temporal distribution of repeating sequences, we find that the quasi-periodic repeating sequences tend to be isolated in space, away from other repeating sequences and the background seismicity. The interactions between closely located repeating sequences concentrated in small areas may affect the their recurrence intervals. During seismically active periods, a reduction of recurrence interval can be seen from the data, which is likely related to the changing stress field. The fault slip rate computed from the size and recurrence intervals of the 29 sequences varies from 1.6 to 10.1 mm·a^-1 at the depth range of 3~12 km, and shows substantial difference among segments.