2017年九寨沟MS7.0地震序列活动特征分析

中强地震序列的主震发生后，短时间内受台站距震中较远、尾波干扰和波形重叠等因素的影响，往往会遗漏大量的地震，而地震目录的完整性会直接影响到震后趋势判定和余震序列特征分析的科学性和可靠性。本文利用基于GPU加速的模板匹配方法对2017年8月1～12日的连续波形进行扫描计算，检测九寨沟M_S7.0地震前后遗漏的地震事件，选取台网目录中信噪比较高的1033个地震事件作为模板，在主震前7天至震后5天期间识别出4854个检测地震事件，为台网可定位目录的3.3倍，除去对台网单台地震事件的修正外，还检测到1797个遗漏地震事件，将完备震级从1.6级降低到1.4级。基于补充了遗漏地震的完整地震目录，对2017年8月8日九寨沟M_S7.0地震序列活动特征进行分析。结果表明，前震序列在主震前短时间内出现了地震活动的密集增强，b值也显示为低值状态，可能是深部断层发生破裂之前的加速蠕动的结果。随着时间的推移，余震序列的完备震级逐渐下降并趋于稳定，b值存在缓慢升高的趋势，未来较长时期内余震序列仍将处于持续衰减的状态。

Temporal evolution of the seismicity of the 2017 Jiuzhaigou MS7.0 earthquake sequence

After the mainshock occurred in moderately strong earthquake sequence, a large number of earthquakes are likely to be missed due to the far distance from the epicenter, the interference of the coda wave and the overlap of the waveform in the short time, but the integrity of seismic catalog directly affects the scientific and reliability analysis of post earthquake trend determination and aftershock sequence characteristic analysis. In this paper, we adopt a matched filter technique based GPU parallel computing method to detect the missing seismic events in the period from August 1, 2017 to August 12, and obtained 4854 detected events by using 1033 events with high signal-to-noise ratio listed in the seismic network catalog as templates. The number of earthquakes detected was 3.3 times as much as that of the network catalog. In addition to the correction of the single earthquake event in the network, 1797 missing earthquake events were detected, and the complete magnitude was reduced from 1.6 to 1.4. Based on the complete earthquake catalog supplemented with missing earthquakes, we analyzed the activity characteristics of the M_S7.0 earthquake sequence on August 8, 2017 in Jiuzhaigou, Sichuan. The results show that:the foreshock sequence had intensive seismicity enhancement, in a short period of time before the mainshock, and the b-value also showed a low value state, which may be the result of accelerated creep before the rupture of a deep fault. As time went by, the complete magnitude of the aftershock sequence decreased gradually and tended to be stable, and the b-value had a slowly rising trend, so the aftershock sequence would remain in a state of sustained decay in the long term.