Ground-Motion Simulation in the Lower Tagus Valley Basin

Abstract

Abstract-Throughout history, the Lower Tagus Valley (LTV) region has been shaken by several earthquakes, including some with moderate to large magnitudes and with sources located inside the basin, for example the 1344 (M6.0) and 1909 (M6.0) earthquakes. Previous simulations (BEZZEGHOUD et al. Natural Hazard 69: 1229-1245, 2011 have revealed strong amplification of the amplitude waves in the region, because of the effect of the lowvelocity sediments that fill the basin. The model used in those simulations was updated in this work by including new highresolution geophysical and geotechnical data available for the area (seismic reflection, aeromagnetic, gravimetric, deep wells, standard penetration tests, and geological data). To contribute to improved assessment of seismic hazard in the LTV, we simulated propagation of seismic waves produced by moderate earthquakes in a 3D heterogeneous medium by using elastic finite-difference wave propagation code. The method, successfully used by GRANDIN et al. (Geophys J Int 171: 1144-1161, involves evaluation of the seismic potential of known faults in the area studied and threedimensional seismic ground motion modelling by use of finite difference methods. On the basis of this methodology, we calculated the ground motion for the April 23, 1909, Benavente (Portugal) earthquake (Mw = 6.0) in dense grid points, then computed the synthetic isoseismic map of the area by use of appropriate relationships between seismic intensity (MMI) and peak ground velocity (PGV). The synthetic results, in contrast with available macroseismic and instrumental data, enable validation of the source models proposed for the area, identification of the sources of historical earthquakes, and could also indicate which areas are more exposed to seismic ground motion.

Effects of Earthquakes on Buildings in the Ibero-Maghrebian Region

“…The greatest damage to buildings in Portugal was registered in the Algarve region, with total or partial collapses spread over different locations, amplified by the so-called site effect [13,14], that is, the amplification of the seismic waves due to the geological characteristics of soils in superficial layers and the soil-structure interaction of buildings. Settlements built on younger tectonic formations, such as poorly consolidated alluvial soils, felt the shakes more strongly [15], increasing the vulnerability of traditional constructions made with extremely poor materials and techniques.…”

Regional correlations for estimating seismic amplification. Implications for loss assessment in SW Iberia

“…The latter are based on data that rely on relationships from earthquake motions elsewhere and surface geology (Borges et al, 2015). The seismic activity of SW Iberia is moderate and earthquakes of Mw<5 are probable (Amaro-Mellado et al, 2017b).…”