In Fonseca et al. we put forward the first results of the paleoseismological investigations underway in the Lower Tagus Valley (LTV), near the Portuguese capital; a region of well-documented historical intraplate earthquakes of magnitude M6.5–M7. Our study focused on the right bank of the Tagus River from Lisbon to Santarem, where a persistent NNE-SSW scarp can be followed in the landscape morphology. We identified deformation of recent deposits in trenches on that scarp, and interpreted it as a thrust geometry with significant left-lateral component. We dated the deformed layers as Holocene using archeological criteria, as well as C14, and measured a minimum displacement of ∼3 m over the last 4000 years. These observations were correlated with the intensity distribution of the destructive 1531 Vila Franca earthquake [Justo and Salwa, 1998], and we concluded that the structure now discovered was the surface rupture due to that earthquake.
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