The fingerprint of structural inheritances in the W-Pyrenees revealed by machine learning detection of seismicity

Abstract

The orogenic evolution of the western Pyrenees and its relationship with ancient rift architecture are well-studied and therefore represent a natural laboratory for investigating the link between structural inheritance and the distribution of present-day seismicity. In this study, we use an automated method to detect and pick P and S waves from local earthquakes to characterize the distribution of seismicity in the region. The P and S picks are used to obtain a catalog of earthquakes and to perform a local earthquake tomography. We analyze 2-D sections and depth slices of the tomographic model and of the seismicity catalog, and confront them to the 3-D geological architecture of the inverted Mauléon rift system. Our results reveal that present-day deformation is mainly extensional, with a main cluster of aligned, steeply north-dipping seismicity localized along the former rift necking domain. In addition, the rift-inherited NNE-SSW Saison and Barlanès transfer zones either offset or disrupt the seismicity cluster and delimit three seismically active segments. The Chaînons Béarnais segment shows localized seismicity, whereas the eastern and western Mauléon segments show a westward extension of earthquake distribution in relation with the widening of both the orogenic wedge and the mantle body preserved at shallow depth. Our results suggest that the rift-inherited necking zone played a predominant role in the localization of the deformation during both orogenic and post-orogenic evolution, and as such represents a critical zone for seismic hazard assessment. Earthquakes diffusely distributed in and around the high-velocity mantle body could be partly related to ongoing serpentinization.