LTV - SourceMod4PSHA Construction of a seismic source model for the Lower Tagus Valley to use in future probabilistic seismic hazard assessment

When aiming for the probabilistic earthquake hazard assessment (PSHA) for a given region, one studies the sources of the seismic waves which might cause damage, their propagation through the earth, and their potential amplification at the sites of interest. 

This project focuses on the first aspect (the construction and the evaluation of models for the seismic sources relevant for the 

Lower Tagus Valley (LTV)), while carrying out the hazard analysis to the production of probabilistic hazard maps. Large earthquakes happened in the past on the SW margin of Portugal and were strongly felt in Lisbon and in its surrounding region (in 1755, moment magnitude Mw 8.5 and on Feb. 28 1969, Mw 7.3). However, large events can also initiate in the LTV itself (see the Mw 6 to 7 earthquakes in 1344, 1531, and 1909). Geophysically-determined fault offsets also point to the recurrence of Mw 6 earthquakes every 2 to 5 thousands of years. Because of the short distances between sites and sources within the LTV, information on the 

lateral extension of faults or seismic source zones will be essential, to use with Ground Motion Prediction Models. The 

challenges will be to collect, combine, and possibly complement information of various types: the historical and 

instrumental earthquake catalogues, mapped active faults, geophysical subsurface data on fault geometry and offsets, and 

paleoseismological information as they become available. A probabilistic modeling framework will be designed and used to 1) 

study the correspondence between faults and earthquakes, and 2) to test the pertinence of different ways of characterizing the 

sources (faults, diffuse zones, etc.) in terms of the robustness of the resulting hazard maps (i.e., maps of expected ground 

shaking level for given return periods). Forward numerical fault modeling will also be instrumental in 1) studying the geometry of 

the faults and the tectonic regimes with respect to the boundary conditions on the region (indeed, discrepancies in the numerical 

models might indicate where probable, yet unknown faults might lie), and 2) propose physics-based renewal models for 

characteristic strong earthquakes. The project will propose a seismicity model ready for use in a PSHA for the LVT, and will identify the inputs the estimation of PSHA in the LTV are most sensitive to. The results of this research will be useful for any region of the world displaying similar seismic activity, and similar tectonic patterns.