Velocity model estimated from seismic refraction survey and MASW, at Flamengos site (Faial island, Azores)

The aim of this communication is to present the velocity models of propagation of seismic waves P and S using geophysical methods, such as refraction surveys and MASW (Multichannel analysis of surface waves). After determining the velocity models, the results were compared for the same location, with the lithology of the island. These results provide important physical parameters used for a near surface characterization of the soil structure and to predict seismic ground motion in this region

Caracterização da estrutura sub-superficial da ilha do Faial (Açores)

The aim of this communication is to present the velocity models of propagation of seismic waves P and S using geophysical methods, such as refraction surveys, MASW (Multichannel Analysis of Surface Waves), and Horizontal-to-Vertical spectral ratio ambient-noise in Faial Island (Azores). After determining the velocity models and ratios H/V, the results were compared for the same location, with previous works of ambient-noise and with lithology of the island. These results providing important physical parameters for a near surface characterization of the soil structure and to predict seismic ground motion in this region

Characterization of an Intraplate Seismogenic Zone Using Geophysical and Borehole Data: The Vila Franca de Xira Fault, Portugal

The Vila Franca de Xira (VFX) fault is a regional fault zone located about 25 km northeastof Lisbon, affecting Neogene sediments. Recent shear-wave seismic studies show thatthis complex fault zone is buried beneath Holocene sediments and is deforming thealluvial cover, in agreement with a previous work that proposes the fault as the sourceof the 1531 Lower Tagus Valley earthquake. In this work, we corroborate these resultsusingS-wave,P-wave, geoelectric, ground-penetrating radar and borehole data, con-firming that the sediments deformed by several fault branches are of Upper Pleistoceneto Holocene. Accumulated fault vertical offsets of about 3 m are estimated from theintegrated interpretation of geophysical and borehole data, including 2D elastic seismicmodeling, with an estimated resolution of about 0.5 m. The deformations affecting theTagus alluvial sediments probably resulted from surface or near-surface rupture of theVFX fault during M∼7 earthquakes, reinforcing the fault as the seismogenic source ofregional historical events, as in 1531, and highlighting the need for preparedness for thenext even

Interplay of tectonics and magmatism during post-rift inversion on the central West Iberian Margin (Estremadura Spur)

ABSTRACT: The combined effects of post-rift magma emplacement and tectonic inversion on the hyper-extended West Iberian Margin are unravelled in detail using multichan nel 2D/3D seismic data. The Estremadura Spur, acting as an uplifted crustal block bounded by two first-order transfer zones, shows evidence of four post-rift tectonic events each with a distinctive seismic-stratigraphic response that can be used to dem onstrate the tectono-magmatic interplay, namely: (a) the Campanian onset of mag matism (including the Fontanelas Volcano, the widespread evidence of multiple sill complexes and the detailed description of a >20 km long laccolith, the Estremadura Spur Intrusion; (b) the Campanian-Maastrichtian NE-SW event pervasively affecting the area, resulting in regional uplift, reverse faulting and folding; (c) the Paleocene mid Eocene inversion that resulted in widespread erosion and; (d) the Oligocene-mid Miocene evidence of rejuvenated NW-SE inversion marked by crestal faulting and forced-fault folding establishing the final geometry of the area. The distinct deforma tion styles within each tectonic phase document a case of decoupled deformation be tween Late Cretaceous and Tertiary units, in response to the predominant stress field evolution, revealing that the magnitude of Late Cretaceous inversion is far more sig nificant than the one affecting the latter units. A detailed analysis of the laccolith and its overburden demonstrate the distinct deformation patterns associated both with magma ascent (including extensional faulting, forced-folding and concentric reverse faulting) and its interference as a rigid intrusive body during subsequent transpres sive inversion. This reinforces the role that the combined tectono-magmatic events played on the margin. Also analysed is the wider impact of post-rift magmatism and the associate emplacement of sub-lithospheric magma on the rheology of a thinned continental crust. This takes into account the simultaneous tectonic inversion of the margin, the implied alternative views on characteristic heat flow, and on how these can be incorporated in source rock organic maturity modelling.info:eu-repo/semantics/publishedVersio

Prospecção geofísica aplicada à detecção de falhas activas – a falha de Vila Franca de Xira)

A falha de Vila Franca de Xira é considerada como a mais provável fonte de vários sismos destrutivos que afetaram a região de Lisboa. Contudo, não há evidência à superfície de deformação nos sedimentos Holocénicos pertencentes ao Vale Inferior do Tejo (VIT), devido à baixa taxa de deslizamento (<1mm/ano) e às altas taxas de erosão/sedimentação. O objetivo é confirmar estudos recentes e verificar se esta falha é ativa, contribuindo para a análise de risco sísmico no VIT, usando métodos geofísicos. Inicialmente, o ensaio de sísmica de reflexão deu indicação de quatro falhas prováveis, e por esta razão realizaram-se perfis de georadar e tomografia elétrica nestes locais específicos. Nos perfis obtidos observaram-se vários deslocamentos verticais, correspondendo aos traçados de falhas propostos em trabalhos anteriores