Abstract:

The Yishu fault zone is located in the middle section of the Tanlu fault zone, consisting of multiple nearly north-northeast trending faults. Significant variations in crustal structure are present on both sides of the fault zone. The seismic velocity and velocity variations are important parameters for understanding the deep structural characteristics of the earth and the potential damage of the medium. Based on the continuous seismic waveforms from permanent stations in the Yishu fault zone and surrounding regions from January 2011 to December 2014, we perform ambient noise tomography to monitor the phase velocity variations of Rayleigh wave. The results show that the velocity variations correlate well with the small earthquake activities. The earthquakes (M>2) are mainly concentrated near the velocity reduction and velocity transition zones. The velocity variations near the Yishu fault zone are not significant, indicating that the fault activity is relatively weak recently. The velocity variations in the Jiaobei uplift are notable between 2013 and 2014, which is related to surface deformation. It is speculated that the compression effect of regional stress is the main factor for the velocity increase in the Jiaobei uplift.

Key words: Yishu fault zone')">Yishu fault zone, ambient noise tomography, velocity variation, small earthquake activity