基于重复地震研究川滇地区主要断裂带的深部变形

发生在同一断层部位上0.5~4.0级的重复地震（也称重复微震）是研究断裂带深部变形的天然（有力）工具.本文系统汇集了川滇地区主要断裂带识别出的76组重复地震研究结果，构建了川滇地区重复地震的时空分布图像和断裂带深部变形时空演化特征，结果表明：丽江-宁蒗断裂带在脆韧转换带约23 km深处的滑动速率为4.3~5.4 mm·a^-1，小江断裂带3.0~12.3 km深处的滑动速率为1.6~10.1 mm·a^-1，红河断裂带北段在6.0~13.4 km深处的滑动速率为2.3~10.0 mm·a^-1，鲜水河断裂带南段3.0~18.7 km深处的滑动速率为3.0~10.2 mm·a^-1，龙门山断裂带在4.0~17.3 km的汶川8.0级地震孕育深处的滑动速率为3.5~9.6 mm·a^-1，龙门山断裂带南端3.6~18.7 km处滑动速率为5.8~10.2 mm·a^-1.综合分析认为：川滇地区主要边界断裂带的深部滑动速率较为一致，揭示了川滇地块和巴颜喀拉地块整体协同变形的特征.由重复微震与深部滑动速率变化构建了孕震深处的变形模式，即重复微震与断裂带局部闭锁段在空间位置上存在密切的关联性，强震前孕震闭锁区存在明显的深浅部构造形变差异，震前存在的深部加速变形过程可能是断层亚失稳阶段的具体表征.

Repeating microearthquakes and deep deformation along the major faults in the Sichuan-Yunnan region,China

Repeating microearthquakes (M < 4) are recurrent ruptures at small fault patches, which provide in-situ information for studying the spatial variation and temporal evolution of subsurface deformation at seismogenic depth. In this study, we compiled a total of 76 repeating earthquake sequences occurring at major faults in the Sichuan-Yunnan region in southwest China. We then employed these sequences to estimate fault slip rates based on their sizes and recurrence intervals. The slip rates estimated at various parts of the study area are 4.3~5.4 mm·a-1 at~23 km deep along the Lijiang and Ninglang faults, 1.6~10.1 mm·a-1 in the depth range of 3.0~12.3 km along the Xiaojiang fault, 2.3~10.0 mm·a-1 at depths between 6.0 and 13.4 km along the northern segment of Honghe fault, 3.0~10.2 mm·a-1 in the depth range of 3.0~18.7 km along the southern segment of Xianshuihe fault, 3.5~9.6 mm·a-1 at depths between 4.0 and 17.3 km along the Longmenshan fault, and 5.8~10.2 mm·a-1 in the depth range of 3.6~18.7 km at the southernmost Longmenshan fault. The observed slip rates among different faults are roughly in the similar range, which may reflect the characteristic of deformation within the Sichuan-Yunnan block and the Bayan Har block. Our results also showed that most of the repeating sequences tend to occur at the edge of asperities of strong earthquakes, suggesting a close spatial correlation between repeating microearthquakes and impending large devastating earthquakes. The slip rates estimated from deep sequences appears to systematically larger than those derived from shallow events. More importantly, there is a sudden acceleration in deep slip rate before strong earthquakes, which may suggest that the asperity is entering its meta-instable state.