Integrated Passive Seismic Imaging of Active and Blind Faults in the North Tabriz Region, Northwestern Iran, Using MSM and HVSR

Blind faults beneath Quaternary sediments pose a seismic hazard in urbanizing regions because they may lack surface expressions. This study integrates two seismic investigations in northern Tabriz, northwestern Iran, to assess the effectiveness of the Microseismic Sounding Method (MSM) and Horizontal-to-Vertical Spectral Ratio (HVSR) analysis for detecting concealed fault-related structures associated with the North Tabriz Fault (NTF). Ambient vibrations were recorded along two profiles using ۲۹ and ۴۰ stations, with ۵۰ m spacing and ۹۰ min recording durations. Power spectral density analysis was used for MSM, while HVSR curves were calculated for one profile. The ۲-۱۰ Hz range provided more stable responses and clearer structural anomalies than the ۰.۲-۲ Hz range. Several vertically continuous low-intensity anomalies were interpreted as fractured or weakened zones. The anomaly near station S۱۷ is interpreted as the North Tabriz Blind Fault. MSM anomalies corresponded with lower HVSR resonance frequencies, demonstrating that their integration provides a practical, non-invasive, cost-effective approach for concealed-fault mapping in urban environments.

کلیدواژه ها:

Microseismic Sounding Method ، HVSR ، ambient vibration ، blind fault ، North Tabriz Fault ، passive seismic ، seismic hazard