High-resolution P- and S-wave reflection studies of an intraplate structure: The Azambuja fault, Portugal

The Azambuja fault is a NNE trending structure located 50 km north of Lisbon, the capital and most populous city Portugal. has been considered as possible source for historical, large earthquakes. Understanding this priority in seismic hazard evaluation region. clear morphological signature. Miocene Pliocene sediments are tilted eastward cut by steeply dipping mesoscale segments, presenting reverse normal offsets with net downthrow to east. Neotectonic studies indicate Quaternary slip on 0.05–0.06 mm/year. However, no direct evidence affecting Pleistocene or Holocene was found so far. Here, we present findings from high-resolution reflection using both P- S-waves over deposits. detection small-throw faulting ductile challenging task. We show that multiple signatures, like perturbations hyperbolae visible shot CMP gathers, interruptions reflectors stacked sections, lateral velocity variations obtained horizon analysis, all at coincident locations, strongly suggest activity affected study area. corroborated wavepath eikonal traveltime tomography analysis supported modeling. By means 2D viscoelastic modeling, explain absence fault-related diffractions negligible back-scattered energy fault. Using data nearby boreholes, find 15 ka old alluvium cover indeed disturbed presence shallow strands. Considering estimated vertical throws empirical relationships between length, co-seismic rupture magnitude, rate 0.07 mm/y, slightly larger than previously thought, expected