Geometrical heterogeneity and variation of mechanical properties along and across active fault zones may affect the seismicity of such faults. Additionally, the nature of host-rocks juxtaposed by the fault representing lithological units of distinct mechanical property plays a key role in controlling the deformation associated with faulting. In this study, we utilized excellent outcrops in Baza sub-basin of Southern Spain along a 30km active intrabasinal fault; namely, Galera Fault (GF), which is geographically exposed at different structural positions. GF acts as a transfer fault that is kinematically coupled with the normal Baza fault to the west. As part of our investigation, we conducted scanline surveys that included structural analysis, in-situ measurements such as Young's Modulus (E) using Schmidt hammer, permeability as well as P-wave velocity (Vp) and XRD analysis from the collected samples. Structural analysis reveals that the orientation of the segments of GF strike slightly changes from north to south, mostly along NE-SW to ENE-WSW and show strike-slip or normal fault kinematics. In the northern sector of GF, XRD analysis suggests that the fault rocks and the corresponding host rocks are calcite rich (~94-99%). On the other hand, the host-rock is very heterogeneous in the central and southern segments with either dolomite or gypsum as the most dominant mineral. E estimates generally show lower values along the fault planes relative to the adjacent host rocks due to the presence of higher proportion of clay minerals in the fault rocks (Figure 1). However, E and Vp in fault rocks exhibit higher values as compared to their adjacent host-rock only when the proportion of calcite in the fault rocks is high coupled with no detectable clay minerals. Our study reveals that compartmentalization of geomechanical properties at different structural positions of active fault zone in Tertiary rocks is significantly controlled by the mineral composition of the host rocks through which the faults cut across. Therefore, we conclude that in addition to the regional tectonic forces, the distribution of the different types of host-rock representing the mechanical stratigraphy of the basin is expected to play a vital role in influencing the style of faulting and seismicity.
Figure 1. Plots showing the distribution of Young's Modulus and location of subsidiary faults along two scanlines oriented along and across the strike of the major fault (GF) in its central segment.
