# Seismic Exploration Methods for Structural Studies and for Active Fault Characterization: A Review
## 5 Active Fault Characterization  
Seismic exploration provides key data to understand subsurface structures and processes associated with faulting. The ability to image with high resolution the earth's subsurface using seismic techniques has significantly contributed to a better understanding of the mechanism of surface rupture of seismogenic faults and holds a great potential to improve hazard assessment [16; 31; 126; 127; 128; 129]. In recent years, the application of high-resolution seismic profiling has emerged as a powerful tool for studying the surface characteristics of active faults. The identification and the study of seismogenic faults at the surface is crucial for seismic hazard assessment. Seismic exploration allows us to investigate fault geometries, fault slip rates, fault segmentation, and associated geological features [17; 128; 130; 131]. Moreover, by analyzing the seismic data in conjunction with other geophysical and geological data sets, we can unravel the geometric and physical attributes of active fault zones, thereby yielding advantageous implications for the assessment of surface faulting hazards and comprehending the intricate interplay between faults and subsurface fluid dynamics (e.g., [PERSON] et al. [17]). The case studies presented below aim to highlight the significance of seismic exploration methods in studying the near-surface features of seismogenic faults. The first example is from [PERSON] et al. [131], who utilized high-resolution seismic profiling to investigate the faulting associated with the 1934 Ms 6.6 Hansel Valley earthquake in Utah, USA. Hansel Valley, situated north of the Great Salt Lake, is a fault-controlled extensional basin within the northeastern basin and range province [132; 133; 134; 135]. The earthquake, which occurred on 12 March 1934, resulted in surface rupture in the southernmost part of Hansel Valley (Figure 8: [PERSON] et al. [131]) and is recognized as Utah's only historic surface-faulting earthquake and one of the largest within the eastern basin and range province and Intermountain Seismic Belt [134]. The earthquake produced an 8 km-long by 3 km-wide zone of north-south trending surface deformation. Despite surface measurements indicating less than 0.5 m of vertical displacement, seismological data suggested mostly strike-slip faulting at depth. The study of [PERSON] et al. [131] aimed to assess the origin of the ruptures occurred during the 1934 Hansel Valley earthquake to gain insights into the way complex fault ruptures accommodate regions of continental extension and transtension. By employing a 6.6 km-long, high-resolution seismic survey, [PERSON] et al. [131] found that the 1934 surface ruptures were not secondary in nature but represented the direct expression of coseismic deformation along numerous shallow faults beneath the valley floor. The seismic data indicate a complex tectonic framework for Hansel Valley, characterized by diffuse faulting and a broad negative flower structure that extends to depths of at least 1 km. Their results suggested that normal-oblique slip faulting is active in Hansel Valley, which is consistent with geological observations made shortly after the earthquake and focal mechanisms [134] implying primarily left-lateral, strike-slip faulting at a seismogenic depth of approximately 8.5 km. [PERSON] et al. [131] explained the apparent discrepancy between shallow and deep fault kinematics through slip partitioning during fault propagation. The researchers proposed that the causative rupture of the 1934 Hansel Valley earthquake occurred most probably along an immature fault zone, where surface deformation was redistributed within a \(\sim\)3 km wide off-fault damage zone. The damage zone is characterized by numerous small-offset, shallow normal-fault strands (Figure 9) that may have been alternately and differentially activated during multiple earthquake episodes at seismogenic depths.