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We have studied the focal mechanisms of the 1980, 1997 and 1998 earthquakes in the Azores region from body-wave inversion of digital GDSN (Global Digital Seismograph Network) and broadband data. For the 1980 and 1998 shocks, we have obtained strikeslip faulting, with the rupture process made up of two sub-events in both shocks, with total scalar seismic moments of 1.9 × 10 19 Nm (M w = 6.8) and 1.4 × 10 18 Nm (M w = 6.0), respectively. For the 1997 shock, we have obtained a normal faulting mechanism, with the rupture process made up of three sub-events, with a total scalar seismic moment of 7.7 × 10 17 Nm (M w = 5.9). A common characteristic of these three earthquakes was the shallow focal depth, less than 10 km, in agreement with the oceanic-type crust. From the directivity function of Rayleigh (LR) waves, we have identified the NW-SE plane as the rupture plane for the 1980 and 1998 earthquakes with the rupture propagating to the SE. Slow rupture velocity, about of 1.5 km/s, has been estimated from directivity function for the 1980 and 1998 earthquakes. From spectral analysis and body-wave inversion, fault dimensions, stress drop and average slip have been estimated. Focal mechanisms of the three earthquakes we have studied, together with focal mechanisms obtained by other authors, have been used in order to obtain a seismotectonic model for the Azores region. We have found different types of behaviour present along the region. It can be divided into two zones: Zone I, from 30°W to 27°W; Zone II, from 27°W to 23°W, with a change in the seismicity and stress direction from Zone I. In Zone I, the total seismic moment tensor obtained corresponded to left-lateral strike-slip faulting with horizontal pressure and tension axes in the E-W and N-S directions, respectively. In Zone II, the total seismic moment tensor corresponded to normal faulting, with a horizontal tension axis trending NE-SW, normal to the Terceira Ridge. The stress pattern for the whole region corresponds to horizontal extension with an average seismic slip rate of 4.4 mm/yr.

The inclusion of site-specific conditions is essential to adequately represent the seismic hazard and the seismic risk for a region. We acquired, gathered and organized a near surface shear-wave velocity database for Portugal, and applied a three-step methodological approach for developing a V S30 site-conditions map using extrapolation based on surface geology. The methodology includes: 1) defining a preliminary set of geologically defined units; 2) calculating the probability distribution of log V S30 for each unit; and 3) merging the units according to the results of statistical tests. The final model comprises three geologically defined units characterized by log V S30 distributions that are statistically significantly different from each other: F1-Igneous, metamorphic and old sedimentary rocks; F2-Neogene and Pleistocene formations; and F3-Holocene formations. The site conditions for F3 unit may be further refined using correlations with topographic slope based on the SRTM3 dataset. We analysed the performance site-conditions models based on correlations with exogenous data (topographic slope and surface geology analogues). The results show that the residual distributions between log V S30 values measured and estimated from those proxies are strongly biased for some geological units, emphasizing the need for acquiring regional V S data.

S U M M A R YThis is the second paper of a series of two concerning strong ground motion in SW Iberia due to earthquakes originating from the adjacent Atlantic area. The aim of this paper is to use the velocity model that was proposed and validated in the companion paper for seismic intensity modelling of the 1969 (M s = 8.0) and 1755 (M = 8.5-8.7) earthquakes.First, we propose a regression to convert simulated values of Peak Ground Velocity (PGV) into Modified Mercalli Intensity (MMI) in SW Iberia, and using this regression, we build synthetic isoseismal maps for a large (M s = 8.0) earthquake that occurred in 1969. Based on information on the seismic source provided by various authors, we show that the velocity model effectively reproduces macroseismic observations in the whole region. We also confirm that seismic intensity distribution is very sensitive to a small number of source parameters: rupture directivity, fault strike and fault dimensions. Then, we extrapolate the method to the case of the great (M = 8.5-8.7) 1755 earthquake, for a series of hypotheses recently proposed by three authors about the location of the epicentral region. The model involving a subductionrelated rupture in the Gulf of Cádiz results in excessive ground motion in northern Morocco, suggesting that the source of the 1755 earthquake should be located further west. A rupture along the western coast of Portugal, compatible with an activation of the passive western Iberian margin, would imply a relatively low average slip, which, alone, would could not account for the large tsunami observed in the whole northern Atlantic ocean. A seismic source located below the Gorringe Bank seems the most likely since it is more efficient in reproducing the distribution of high intensities in SW Iberia due to the 1755 earthquake.

In probabilistic seismic-hazard analysis (PSHA), seismic source zone (SSZ) models are widely used to account for the contribution to the hazard from earthquakes not directly correlated with geological structures. Notwithstanding the impact of SSZ models in PSHA, the theoretical framework underlying SSZ models and the criteria used to delineate the SSZs are seldom explicitly stated and suitably documented. In this paper, we propose a methodological framework to develop and document SSZ models, which includes (1) an assessment of the appropriate scale and degree of stationarity, (2) an assessment of seismicity catalog completeness-related issues, and (3) an evaluation and credibility ranking of physical criteria used to delineate the boundaries of the SSZs. We also emphasize the need for SSZ models to be supported by a comprehensive set of metadata documenting both the unique characteristics of each SSZ and the criteria used to delineate its boundaries. This procedure ensures that the uncertainties in the model can be properly addressed in the PSHA and that the model can be easily updated whenever new data are available. The proposed methodology is illustrated using the SSZ model developed for the Azores-West Iberian region in the context of the Seismic Hazard Harmonization in Europe project (project SHARE) and some of the most relevant SSZs are discussed in detail.Online Material: Tables describing characteristics and boundaries of the seismic source zones.

a b s t r a c t a r t i c l e i n f oIn this paper we present a new basement (defined here as Paleozoic, Precambrian and Mesozoic igneous rocks) map of the Lower Tagus Valley area. This map is a contribution to the understanding of the structural evolution of the top of the basement in the Lower Tagus Valley area during the Mesozoic and Cenozoic Eras. The map was produced using aeromagnetic, well, seismic reflection and geological outcrop data. It shows unprecedented details of the geometry of the basement rock's surface with higher resolution and covers a larger area than the previous basement map of the study area. In spite of an estimated average error of 200 m in depth and an horizontal resolution of 4 km, our map not only reproduces with accuracy several well known basement structures but it also emphasizes previously unknown features. Major basement faults were inferred from large depth variations at the top of the basement, magnetic 2D Euler deconvolution and horizontal gradient analysis and are compatible with surface geological structures, well data and hydrogeological information. Implications to the geodynamic evolution of the SW European Variscides and consequences to Meso-Cenozoic tectonics are discussed. The correlation of the basement structures with instrumental seismicity is carried out and their neotectonic activity is discussed on the basis of existing geological outcrop data.

This study examines the long profiles of tributaries of the Tagus and Zêzere rivers in Portugal (West Iberia) in order to provide new insights into patterns, timing, and controls on drainage development during the Quaternary incision stage. The studied streams are incised into a relict culminant fluvial surface, abandoned at the beginning of the incision stage. The streams flow through a landscape with bedrock variations in lithology (mainly granites and metasediments) and faulted blocks with distinct uplift rates. The long profiles of the analyzed streams record an older transitory knickpoint/knickzone separating (1) an upstream relict graded profile, with lower steepness and higher concavity, that reflects a long period of quasi-equilibrium conditions reached after the beginning of the incision stage, and (2) a downstream rejuvenated long profile, with steeper gradient and lower concavity, particularly for the final reach, which is often convex. The rejuvenated reaches testify to the upstream propagation of several incision waves, interpreted as the response of each stream to increasing crustal uplift and prolonged periods of base-level lowering by the trunk drainages, coeval with low sea level conditions. The morphological configurations of the long profiles enabled spatial and relative temporal patterns of incisions to be quantified. The incision values of streams flowing on the Portuguese Central Range (PCR; ca. 380-150 m) are variable but generally higher than the incision values of streams flowing on the adjacent South Portugal Planation Surface (SPPS; ca. 220-110 m), corroborating differential uplift of the PCR relative to the SPPS. Owing to the fact that the relict graded profiles can be correlated with the Tagus River T1 terrace (1.1-0.9 My) present in the study area, incision rates can be estimated (1) for the streams located in the PCR, 0.38-0.15 m/ky and (2) for the streams flowing on the SPPS, 0.22-0.12 m/ky. The differential uplift inferred in the study area supports the neotectonic activity of the bordering faults, as proposed in previous studies based upon other geological evidence.

Over the past decade, high-resolution noninvasive sensors have been widely used in explorations of the first few meters underground at archaeological sites. However, remote sensing actions aimed at the study of structural elements that require a very high resolution are rare. In this study, layer characterization of the floor mosaic substrate of the Pisões Roman archaeological site was carried out. This work was performed with two noninvasive techniques: 3D ground penetrating radar (3D GPR) operating with a 1.6 GHz central frequency antenna, which is a very high-resolution geophysical method, and photogrammetry with imagery obtained by an unmanned aerial vehicle (UAV), which is a very high-resolution optical method. The first method allows penetration up to 30-40 cm depth and 3D models can be obtained, and with the second method, very high detail surface images and digital surface models can be obtained. In this study, we analyze a combination of data from both sensors to study a portion of the floor mosaic of the Pisões Roman Villa (Beja, Portugal) to obtain evidence of the inner structure. In this context, we have detected the main structural levels of the Roman mosaic and some internal characteristics, such as etched guides, internal cracking, and detection of higher humidity areas. The methodology that we introduce in this work can be referenced for the documentation of ancient pavements and may be used prior to carrying out preservation activities. Additionally, we intend to show that a Roman mosaic, understood as an archaeological structure, does not consist of only beautiful superficial drawings defined by the tesserae, but these mosaics are much more complex elements that must be considered in their entirety for preservation.