# Seismic Exploration Methods for Structural Studies and for Active Fault Characterization: A Review
## 5 Active Fault Characterization
The findings of the study demonstrated the usefulness of using dense, wide-aperture seismic reflection profiling for the high-resolution exploration of a basin-range fault system that exhibits minor surficial expressions and/or has long recurrence intervals. Figure 8: Simplified geological map of the Hansel Valley from [PERSON] et al. [136]. The figure, modified from [PERSON] et al. ([131]), shows the relationship of the CDP locations along the seismic profile (black line, yellow dots are the CDP locations) to the main surface ruptures associated to the 1934, M = 6.6 Hansel Valley earthquake and to other earthquakes in the valley. Surface ruptures intersecting the seismic profile or projected on it (dashed) are labeled R1 to R11. Symbols: (Qao) Older alluvial deposits; (Ql) Lake Bonneville deposits; (Qm) Marshes; (PP) Oquirrh Formation (see [PERSON] et al. [136]). (h1) Focal mechanism solution for the 1934, M 6.6 Hansel Valley earthquake. (h10); Focal mechanism solution for a 2013, M 3.6 earthquake. [PERSON] et al. [16] provide another fascinating application of high-resolution seismic imaging on active faults. Their research focused on the Alpine Fault system located on New Zealand's South Island (see [PERSON] et al. [137] and references therein). By utilizing high-resolution seismic reflection and ground-penetrating radar (GPR) data across the Alpine Fault, the authors aimed to enhance their understanding of this active fault beyond the limitations of conventional paleoseismological methods [13; 14]. New Zealand's South Island accommodates two active subduction zones: the west-striking Hikurangi subduction zone in the north is connected to the east-striking Puysegur subduction zone in the south through the Alpine Fault zone and a broad zone of oblique compression (Figure 10). Historical and instrumental records of seismicity do not fully capture the earthquake cycle of these fault zones due to the relatively short duration of available records (\(\sim\)200 years and \(\sim\)50 years for historical and instrumental seismicity, respectively) compared to the estimated recurrence intervals of the active faults, which span several hundred years [138]. Therefore, paleoseismic studies play a crucial role in characterizing the numerous active faults that extend across the country (see [PERSON] et al. [137] and references therein). These studies indicate that the Alpine Fault, in the central and southern parts of the South Island, accounts for two-thirds to three-quarters of the 35-38 mm/y of relative motion between the Australian and Pacific plates. The remaining motion is distributed over a 150-200 km-wide region encompassing the Southern Alps and adjacent areas to the east (Figure 10; see [PERSON] et al. [139] and references therein). Figure 9: Seismic interpretation of the first 500 m of the post-stack migrated seismic profile of the western portion of the basin ((**C**): CDP 1250–2540) overlain and compared with the uninterpreted seismic data (**D**) and with the results of Vp refraction tomography (**A**). All images are plotted with the same horizontal and vertical scale. Elevations (**B**) have instead a vertical exaggeration of \(\sim\)12.5%. Blue triangles indicate the surface projection of interpreted faults; red triangles show the location of the surface ruptures associated with the 1934, M 6.6 earthquake and intersecting the seismic profile. Pink triangles are surface ruptures projected on the seismic line. For rupture locations, see Figure 8. All other symbols and seismic units and unconformities are the same as in Figure 8. Modified from [PERSON] et al. [129]. To extend the capabilities of conventional paleoseismological methods, [PERSON] et al. [16] employed an ultra-high-resolution 2D seismic reflection data set and a pseudo-3D seismic reflection data set across the Alpine Fault zone (Figure 10). Their pseudo-3D survey involved detonating explosive charges, which were simultaneously recorded by receivers positioned along two parallel lines.