09 Aug 2023
 | 09 Aug 2023
Status: this preprint is open for discussion.

Networks of geometrically coherent faults accommodate Alpine tectonic inversion offshore SW Iberia

Tiago M. Alves

Abstract. The structural styles and magnitudes of Alpine tectonic inversion are reviewed for the Atlantic margin of SW Iberia, a region known for its historical earthquakes, tsunamis, and associated geohazards. Reprocessed, high-quality 2D seismic profiles provide new images of 26 faults, which were mapped to a depth exceeding 10 km for the first time in this work. The faults are mostly syn-rift structures accommodating vertical uplift and horizontal advection (shortening) during Alpine tectonics. At a regional scale, tectonic reactivation has been marked by: a) the exhumation of parts of the present-day continental shelf, b) local folding and thrusting of sediment at the foot of the continental slope, and c) oversteepening of syn- and post-rift strata near reactivated faults (e.g. ‘passive uplift’). This work proves, for the first time, that geometric coherence dominated the growth and linkage of offshore faults in SW Iberia; thus, they are prone to reactivate as a kinematically coherent fault network. Importantly, they form 100–250 km long structures, the longest of which may generate earthquakes with a momentum magnitude (Mw) greater than 8.0. Tectonic inversion started in the Late Cretaceous and its magnitude is greater close to where magmatic intrusions are identified at depth. In contrast to previous models, this work postulates that regions where Late Mesozoic magmatism was more intense comprise thickened, harder crust, forming lateral buttresses to NW-SE compression. It shows these structural buttresses to have promoted the development of early stage fold-and-thrust belts – typical of convergent margins – in two sectors of SW Iberia.

Tiago M. Alves

Status: open (until 14 Oct 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on egusphere-2023-1671', Gang Rao, 08 Sep 2023 reply
  • RC1: 'Comment on egusphere-2023-1671', Gang Rao, 09 Sep 2023 reply
    • AC1: 'Reply on RC1', Tiago Alves, 21 Sep 2023 reply

Tiago M. Alves


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Short summary
Alpine tectonic inversion is reviewed for SW Iberia, known for its historical earthquakes and tsunamis. High-quality 2D seismic data image 26 faults mapped to a depth exceeding 10 km. Normal faults accommodated important vertical uplift and shortening. They are 100–250 km long and may generate earthquakes with Mw > 8.0. Regions of Late Mesozoic magmatism comprise thickened, harder crust, forming lateral buttresses to compression, promoting the development of fold-and-thrust belts.