# Seismic Exploration Methods for Structural Studies and for Active Fault Characterization: A Review
## 5 Active Fault Characterization
This acquisition strategy ensured a uniform and dense distribution of seismic traces with offset and allowed us to simplify critical processing steps, although it had limitations on the azimuthal range of source-receiver raypaths. According to [PERSON] et al. [16], this cost-effective acquisition strategy may be an alternative to full 3D surveying methods in those fault zones where variations in structure along the fault strike are expected to be less pronounced than in the orthogonal direction. Preliminary interpretations from their study suggest that the primary strand within the shallow Alpine Fault zone exhibits a steep dip and relatively planar characteristics in the late Quaternary sediments and basement down to a depth of at least 150 m. The authors also show that the  
Figure 10: **(Upper left)**: Plate tectonic setting of New Zealand’s South Island showing the west-directed Hikurangi subduction zone in the north, the east-directed Puysegur subduction zone in the south, and the Alpine Fault (modified from [PERSON] et al. [16]). Also labeled with (1) is the northern section of the Alpine Fault zone, i.e., site of the ultra-high-resolution investigation conducted by [PERSON] et al. [16]. **(Upper right)**: Migrated pseudo-3D volume, highlighting the Alpine Fault strand and geological units A1-to-C2 discussed in [PERSON] et al. [16]. **(Lower panel)**: Migrated and depth-converted ultra-high-resolution 2D section showing a borehole intersects gravels (white), an unidentifiable zone (gray), and schist basement (black) in which it terminates at 83 m (from [PERSON] et al. [16]). joint interpretation of 2D and pseudo-3D seismic images, with GPR data, provides further insights into the distribution of subtle deformation structures within the shallow sediments. The two examples above show that seismic methods can deliver additional information useful to enhance our understanding of near-surface active faults. However, when dealing with complex fault structures or weak surface expressions, the real breakthrough lies in the integration of multi-parametric data. A case of complex structure is represented by the Irpinia Fault, the source of the 4 th largest Italian earthquake of the last century (1980, Ms 6.9, Irpinia earthquake; [140; 141], which was recognized solely after the 1980 earthquake throughoseismic scarps and the timing of paleo-events observed on different sectors of the fault by [PERSON] et al. [141]. Their findings suggest that the Irpinia Fault represents a major seismogenic source in the southern Apennines, which is a region of Italy known for its potential to generate up to M7 earthquakes and is therefore included among the areas with the highest seismogenic potential in the Mediterranean region. Recently, [PERSON] et al. [142] conducted a multidisciplinary geophysical study on an active fault strand of the Irpinia Fault in an intramontane basin of the southern Apennines. Their aim was to achieve an accurate 3D geophysical imaging of the shallow structure of the fault zone by integrating a conspicuous multivariate dataset. The test site had previously been the focus of several high-resolution 2D seismic surveys by [PERSON] et al. [131], who highlighted the three-dimensional nature of the fault strand and emphasized the fact that in the southern Apennines, often, the classical analysis of short-term morpho-tectonic indicators observed at the surface alone is insufficient for active fault detection and characterization. [PERSON] et al. [142] complemented the geophysical survey initiated in 2010 with a comprehensive dataset composed of a microgravitmetric survey, 3D and 2D electrical resistivity measurements, 3D and 2D seismic reflection data, aeromagnetic and GPR surveys conducted by drone, and a detailed sampling of CO\({}_{2}\) surface degassing across the fault surface rupture. In general, the integration of multivariate datasets has the potential to greatly reduce the interpretation risk and increase our understanding of the mechanism of active faulting in the near surface.