Integrated Application of Microseismic Sounding and HVSR Methods for Subsurface Fault Detection in the North Tabriz Region, Iran

Abstract

Seismic hazard assessment before earthquake occurrence is a critical component of risk mitigation in urban environments, particularly in seismically active metropolitan areas such as Tabriz, Iran. One of the foundational steps in detailed seismic micro-zonation is the accurate identification and characterization of seismic sources, including active and blind faults. This study integrates geotechnical and passive geophysical methods to delineate fault zones in the northern Tabriz region, with a focus on detecting the North Tabriz Fault and associated blind faults concealed beneath Quaternary alluvial deposits. Two passive seismic techniques, the Horizontal-to-Vertical Spectral Ratio method and the Micro-seismic Sounding Method, were employed to process ambient vibration data collected along two profiles. The joint interpretation of the results, in conjunction with geological and geomorphological information, enabled the identification of several subsurface anomalies. Notably, the subsurface imaging revealed clear signatures of the North Tabriz Blind Fault and other previously unmapped faults. The findings demonstrate a strong correlation between passive seismic data, geological observations, and geoelectrical surveys, validating the reliability and effectiveness of the Horizontal-to-Vertical Spectral Ratio method and the Micro-seismic Sounding Method for detecting subsurface faults in complex tectonic settings.