SISMOD / LISMOT - Finite Seismic Source Modeling by Joint Inversion of Seismic and Geodesic Data and Strong ground motion in the Lower Tagus Valey

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Publications

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

Publication . Carvalho, João; Alves, Daniela; Cabral, João; Ghose, Ranajit; Borges, José Fernando; Dias, Ruben Pereira; Ramalho, Elsa; Caldeira, Bento; Casacão, J.; Leote, Jaime

ABSTRACT: The Vila Franca de Xira (VFX) fault is a regional fault zone located about 25 km northeast of Lisbon, affecting Neogene sediments. Recent shear-wave seismic studies show that this complex fault zone is buried beneath Holocene sediments and is deforming the alluvial cover, in agreement with a previous work that proposes the fault as the source of the 1531 Lower Tagus Valley earthquake. In this work, we corroborate these results using S-wave, P-wave, geoelectric, ground-penetrating radar and borehole data, confirming that the sediments deformed by several fault branches are of Upper Pleistocene to Holocene. Accumulated fault vertical offsets of about 3 m are estimated from the integrated interpretation of geophysical and borehole data, including 2D elastic seismic modeling, with an estimated resolution of about 0.5 m. The deformations affecting the Tagus alluvial sediments probably resulted from surface or near-surface rupture of the VFX fault during M similar to 7 earthquakes, reinforcing the fault as the seismogenic source of regional historical events, as in 1531, and highlighting the need for preparedness for the next event.

2020Journal article

Open access

SedDARE-IB: an open-access repository of sediment data for the Iberian Peninsula and its continental margins

Publication . Torne, Montserrat; Alves, Tiago M.; Jimenez-Munt, Ivone; Carvalho, João; Ayala, Conxi; Ramalho, Elsa; Gomez-Garcia, Angela Maria; Matias, Hugo; Heida, Hanneke; Balaguera, Abraham; Garcia-Lobon, Jose Luis; Verges, Jaume

ABSTRACT: Sediments provide valuable information for geologists and geophysicists whenever they strive to understand, and reproduce, the geological evolution, lithology, rock properties, seismic response, and geohazards of a region. The analysis of sedimentary sequences is thus useful for the interpretation of depositional environments, sea-level change, climate change, and recognition of the sediments' source areas. By integrating sedimentary data into geophysical modeling, such interpretations are improved in terms of their accuracy and reliability. To further help our understanding of the Iberian Peninsula's geological evolution, geological resources, and geohazards, this work presents to the scientific community the SedDARE-IB data repository. This repository includes available data on the depth to the Base of the Cenozoic and Top of the Paleozoic stratigraphic markers for the Iberian Peninsula, the surrounding West Iberian Atlantic Margin and Western Mediterranean Neogene basins, or the acoustic basement as interpreted for the Valencia Trough and Alboran Mediterranean basins. As an example of the broad applicability of the data included in SedDARE-IB, we investigate how sediment thickness affects the depth to the 150 degrees C isotherm in specific basins, as commonly used in geothermal exploration. The calculated trend suggests that, given constant measured surface heat flow and thermal conductivity, the 150 degrees C isotherm becomes shallower as the sediment thickness increases, until a critical threshold value is reached for the latter. The SedDARE-IB database has been compiled thanks to a Portuguese-Spanish collaboration promoting open data exchange among institutions and research groups. SedDARE-IB is freely available at 10.20350/digitalCSIC/16277 (Torne et al., 2024), bringing opportunities to the scientific, industrial, and educational communities for diverse applications.

2025-03Journal article

Open access