Thrust–wrench interference between major active faults in the Gulf of Cadiz (Africa–Eurasia plate boundary, offshore SW Iberia): Tectonic implications from coupled analog and numerical modeling

Abstract

Analog and numerical modeling experiments were carried out to investigate the tectonic interference between intersecting major active strike–slip and thrust faults in the Gulf of Cadiz (Africa–Eurasia plate boundary, offshore SW Iberia). The obtained results show that newly mapped tectonic features located in the fault intersection area (corner zone) consist mostly in oblique (dextral-reverse) faults that accommodate significant strain partitioning. Modeling of this corner-zone faults show that they have endured some degree of rotation, displaying successive evolving geometries and kinematics. Numerical modeling results further show that an interbedded shallow soft layer, accounting for a regional (Late Miocene) gravitational “Chaotic” unit, could explain the mild bathymetric expression of the fault pattern in the corner-zone. Moreover, a recognized depth discrepancy, between the (upper crust) interference fault-pattern and the (lithospheric mantle) seismicity, is interpreted as a manifestation of similar thrust–wrench tectonic interference at different lithospheric depths. Accordingly, an intermediate lower crust–upper mantle aseismic (i.e. softened) depth-domain could be explained by pervasive alteration/serpentinization, prompted by fluid percolation through fault-related fractures associated with the newly revealed corner zone fault-network. Overall obtained results reinforce the relevance of a thrust–wrench multi-rupture seismic scenario as the main cause for the moderate seismicity (Mw<6.0) in the study area.