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Earthquake hazard analyses rely on seismogenic source models. These are designed in various fashions, such as point sources or area sources, but the most effective is the three-dimensional representation of geological faults. We here refer to such models as fault sources. This study presents the European Fault-Source Model 2020 (EFSM20), which was one of the primary input datasets of the recently released European Seismic Hazard Model 2020. The EFSM20 compilation was entirely based on reusable data from existing active fault regional compilations that were first blended and harmonized and then augmented by a set of derived parameters. These additional parameters were devised to enable users to formulate earthquake rate forecasts based on a seismic-moment balancing approach. EFSM20 considers two main categories of seismogenic faults: crustal faults and subduction systems, which include the subduction interface and intraslab faults. The compiled dataset covers an area from the Mid-Atlantic Ridge to the Caucasus and from northern Africa to Iceland. It includes 1248 crustal faults spanning a total length of ∼95100 km and four subduction systems, namely the Gibraltar, Calabrian, Hellenic, and Cyprus arcs, for a total length of ∼2120 km. The model focuses on an area encompassing a buffer of 300 km around all European countries (except for Overseas Countries and Territories) and a maximum of 300 km depth for the subducting slabs. All the parameters required to develop a seismic source model for earthquake hazard analysis were determined for crustal faults and subduction systems. A statistical distribution of relevant seismotectonic parameters, such as faulting mechanisms, slip rates, moment rates, and prospective maximum magnitudes, is presented and discussed to address unsettled points in view of future updates and improvements. The dataset, identified by the DOI https://doi.org/10.13127/efsm20 (Basili et al., 2022), is distributed as machine-readable files using open standards (Open Geospatial Consortium). [ABSTRACT FROM AUTHOR]

In this work, we present both 1-D and 3-D shear wave velocity (Vs) models of the oceanic crust and uppermost mantle below the Deep OCean Test ARray area, located ∼ 70 km north of the central section of the Gloria Fault, in the eastern North-Atlantic Ocean. The velocity models are inferred from the dispersion of surface waves recorded on ocean bottom seismometers. Dispersion measurements are obtained from the analysis of ambient seismic noise at short periods (< 14 s) and teleseismic surface waves at long periods (> 14 s) using the two-station method. The 1-D Vs model is inferred from the joint inversion of Rayleigh wave phase velocities and Love wave group and phase velocities. The 3-D tomographic model is obtained by inversion of 2-D Love wave group velocity maps as a function of depth, further constrained by the average of Love wave phase velocities obtained from ambient noise (4–9 s) and the average Rayleigh and Love wave phase velocities calculated from teleseismic data (14–44 s). The 1-D Vs model shows a sediment layer with a low velocity of 1.05 km s−1, similar to previous studies in the region. Below the sediments, we find an oceanic crust with velocities ranging from 3.3 to 4.5 km s−1. The model reaches an unusually high velocity of 4.9 km s−1 in a 20 km thick layer at depths between 16 and 36 km. We interpret this fast velocity layer as indicative of the presence of harzburgite, a residue of enhanced melting that might have been formed by the proximity between the Mid-Atlantic Ridge and the Azores mantle plume. At greater depths the velocity decreases, forming a low-velocity zone that reaches a minimum at ∼ 70 km depth, which we interpret as the maximum depth for the lithosphere–asthenosphere boundary. The 3-D model shows a structure that is mostly horizontally layered, with Vs isocontours at 3.5–4.5 km s−1 highlighting oscillations of the crustal structure with wavelengths of ∼25–30 km. These oscillations may be due to changes in the rate of mantle upwelling and magma supply rate. [ABSTRACT FROM AUTHOR]

Seismic swarms have been observed for more than 40 yr along the coast of Nordland, Northern Norway. However, the detailed spatio-temporal evolution and mechanisms of these swarms have not yet been resolved due to the historically sparse seismic station coverage. An increased number of seismic stations now allows us to study a nearly decade-long sequence of swarms in the Jektvik area during the 2013–2021 time window. Our analysis resolves four major groups of seismic events, each consisting of several spatial clusters, that have distinct spatial and temporal behaviours. Computed focal mechanism solutions are predominantly normal with NNE–SSW strike direction reflecting a near-vertical maximum principal stress and a NW–SE near-horizontal minimum principal stress, which are controlled by local NW–SE extension. We attribute the swarms to fluid-saturated fracture zones that are reactivated due to this local extension. Over the time period, the activity tends to increase between February and May, which coincides with the late winter and beginning of spring time in Norway. We hypothesize that the seismicity is modulated seasonally by hydrological loading from snow accumulation. This transient hydrological load results in elastic deformation that is observed at local Global Navigation Satellite System stations. The loading is shown to promote failure in a critically stressed normal faulting system. Once a segment is activated, it can then also trigger neighboring segments via stress transfer. Our new results point to a close link between lithosphere and hydrosphere contributing to the occurrence of seismic swarm activity in northern Norway. [ABSTRACT FROM AUTHOR]

Earthquake hazard analyses rely on the availability of seismogenic source models. These are designed in different fashions, such as point sources or area sources, but the most effective is the three-dimensional representation of geological faults. We here refer to such models as fault sources. This study presents the European Fault-Source Model 2020 (EFSM20), which formed the basis for one of the primary input datasets of the recently released European Seismic Hazard Model 2020. The EFSM20 compilation was entirely based on reusable data from existing active fault regional compilations that were first blended and harmonized and then augmented by a set of derived parameters. These additional parameters were devised to enable users to formulate earthquake rate forecasts based on a seismic-moment balancing approach. EFSM20 considers two main categories of seismogenic faults: crustal faults and subduction systems. The compiled dataset covers an area from the Mid-Atlantic Ridge to the Caucasus and from northern Africa to Iceland. It includes 1,248 crustal faults spanning a total length of ~95,100 km and four subduction systems, namely the Gibraltar, Calabrian, Hellenic, and Cyprus Arcs. The model focuses on an area encompassing a buffer of 300 km around all European countries (except for Overseas Countries and Territories, OTCs) and a maximum of 300 km depth for the subducting slabs. All the parameters required to develop a seismic source model for earthquake hazard analysis were determined for crustal faults and subduction systems. A statistical distribution of relevant seismotectonic parameters, such as faulting mechanisms, slip rates, moment rates, and prospective maximum magnitudes, is presented and discussed to address unsettled points in view of future updates and improvements. The dataset, identified by the DOI https://doi.org/10.13127/efsm20, is distributed as machine-readable files using open standards (Open Geospatial Consortium). [ABSTRACT FROM AUTHOR]

We present a new high-resolution 3-D shear wave velocity (V s) model of the crust and uppermost mantle beneath Portugal, inferred from ambient seismic noise tomography. We use broad-band seismic data from a dense temporary deployment covering the entire Portuguese mainland between 2010 and 2012 in the scope of the WILAS project. Vertical component data are processed using phase correlation and phase weighted stack to obtain empirical Green functions (EGFs) for 2016 station pairs. Further, we use a random sampling and subset stacking strategy to measure robust Rayleigh-wave group velocities in the period range 7–30 s and associated uncertainties. The tomographic inversion is performed in two steps: First, we determine group-velocity lateral variations for each period. Next, we invert them at each grid point using a new trans-dimensional inversion scheme to obtain the 3-D shear wave velocity model. The final 3-D model extends from the upper crust (5 km) down to the uppermost mantle (60 km) and has a lateral resolution of ∼50 km. In the upper and middle crusts, the V s anomaly pattern matches the tectonic units of the Variscan Massif and Alpine basins. The transition between the Lusitanian Basin and the Ossa Morena Zone is marked by a contrast between moderate- and high-velocity anomalies, in addition to two arched earthquake lineations. Some faults, namely, the Manteigas–Vilariça–Bragança fault and the Porto–Tomar–Ferreira do Alentejo fault, have a clear signature from the upper crust down to the uppermost mantle (60 km). Our 3-D shear wave velocity model offers new insights into the continuation of the main tectonic units at depth and contributes to better understanding the seismicity of Portugal. [ABSTRACT FROM AUTHOR]

In this article, we validate the neuro‐fuzzy kinematic finite‐fault inversion method by studying the rupture process of the Mw6.2, Aug/24/2016, Amatrice, central Italy, earthquake. We jointly invert three different datasets to infer the spatio‐temporal slip distribution, namely static and high‐rate GNSS data (<=0.06 Hz) and strong‐motion data (0.06−0.5 Hz). Each data set is used to constrain a different frequency range of the source model, depending on the sensitivity of the data set. The inferred slip shows a slow nucleation phase at shallow depths of 3–4 km, followed by a bilateral rupture that forms two asperities, one to the NW (Norcia) and another to the SE (Amatrice) of the hypocenter. Our inferred slip is compared with those previously obtained using well‐established methods. In order to select an adequate number of fuzzy basis functions, we propose two alternative procedures, which yield the same general slip features. The first approach consists of ensuring that the inverse problem is formally over‐determined and uses the same number of basis functions at all frequencies. The second approach is based on a maximum‐likelihood analysis of the model misfit and selects a different number of basis functions for each frequency. The maximum‐likelihood approach allows for more basis functions at high frequencies, where more detail in the spatial slip distribution is needed. The solution obtained with the maximum‐likelihood approach provides a more physically plausible source time function, which shows less back slip artifacts. The accurate prediction of high‐rate GNSS traces not used in the inversion attests the robustness of the inferred slip model. Plain Language Summary: The accuracy of the earthquake's slip imaging method proposed in the companion article by Kheirdast et al. (2021), is tested using data recorded during the 2016 Mw6.2, Amatrice, earthquake. Many previously well‐understood features of the rupture process of this earthquake are well retrieved by the proposed method, including a slow nucleation phase, a bilateral rupture and a high‐amplitude slip patch to the NW of the hypocenter. We present a new strategy to spatially discretize the fault plane, which maximizes the inversion power by taking into account the uncertainty at different frequencies. Key Points: The neuro‐fuzzy kinematic finite‐fault inversion is used to study the Amatrice earthquake and the inferred slip model is compared with previous studiesWe present a new maximum‐likelihood strategy to select an adequate, problem‐specific number of fuzzy basis functionsThe inferred source model is able to correctly predict high‐rate GNSS waveforms not used in the inversion [ABSTRACT FROM AUTHOR]

Kinematic finite‐fault source inversions aim at resolving the spatio‐temporal evolution of slip on a fault given ground motion recorded on the Earth's surface. This type of inverse problem is inherently ill posed due to two main factors. First, the number of model parameters is typically greater than the number of independent observed data. Second, small singular values are generated by the discretization of the physical rupture process and amplify the effect of noise in the inversion. As a result, one can find different slip distributions that fit the data equally well. This ill posedness can be mitigated by decreasing the number of model parameters, hence improving their relationship to the observed data. In this study, we propose a fuzzy function approximation approach to describe the spatial slip function. In particular, we use an Adaptive Network‐based Fuzzy Inference System (ANFIS) to find the most adequate discretization for the spatial variation of slip on the fault. The fuzzy basis functions and their respective amplitudes are optimized through hybrid learning. We solve this earthquake source problem in the frequency domain, searching for optimal spatial slip distribution independently for each frequency. The approximated frequency‐dependent spatial slip functions are then used to compute the forward relationship between slip on the fault and ground motion. The method is constrained through Tikhonov regularization, requiring a smooth spatial slip variation. We discuss how the number of model parameters can be decreased, while keeping the inversion stable and achieving an adequate resolution. The proposed inversion method is tested using the SIV1‐benchmark exercise. Plain Language Summary: Earthquake kinematic source inversions help seismologists infer key features of fault ruptures from the available recorded data. The technique faces inherent ill posedness from the viewpoint of its mathematical formulation. Furthermore, the limited available datasets render the problem even more challenging. In this study, we use an adaptive function approximation methodology that describes slip on the fault using a reduced number of model parameters. This innovative formulation helps us to achieve a good balance between available data (information) and model parameters (unknowns). The proposed technique decreases the degree of ill posedness of the inverse problem by adaptively improving the slip discretization and the slip amplitude using neural network learning. Key Points: We present a new method to kinematically image finite‐fault rupture which reduces the number of basis to spatially discretize the slipThe inversion employs a neural‐network based evolutionary method that improves model estimationWe discretize the fault using fuzzy basis functions that stabilizes the inversion and reduces the number of small singular values [ABSTRACT FROM AUTHOR]

The Canary and Madeira provinces in the Central‐East Atlantic Ocean are characterized by an irregular spatio‐temporal distribution of volcanism along the hotspot tracks, and several alternative scenarios have been suggested to explain it. Here, we combine results from seismic tomography, shear‐wave splitting and gravity along with plate reconstruction constraints to investigate the mantle structure and dynamics beneath those provinces. We find that the Central‐East Atlantic Anomaly (CEAA), which rises from the core‐mantle boundary and stalls in the topmost lower mantle, is the deep source of distinct upper‐mantle upwellings beneath the region. The upwellings detach intermittently from the top of the CEAA and appear to be at different evolutionary stages. We argue that the accumulation of plume material in the topmost lower mantle can play a key role in governing the first‐order spatio‐temporal irregularities in the distribution of hotspot volcanism. Plain Language Summary: The Canary and Madeira provinces, located in the Central‐East Atlantic Ocean, show lineaments of volcanic islands and seamounts, known as hotspot tracks, which differ from most other tracks for their irregular distribution. These lineaments cannot be easily explained by the African plate movement over a fixed, narrow plume of hot mantle material rising from the deep Earth and alternative mechanisms may be required. Here, we integrate observations from seismology and gravity to demonstrate that some first‐order spatio‐temporal irregularities of volcanism in both provinces are due to small‐scale upper‐mantle plumes ("plumelets"), which sporadically rise from the top of a wide lower‐mantle low‐velocity structure, here named "Central‐East Atlantic Anomaly" (CEAA). The CEAA extends vertically from the base of the African large low‐shear‐velocity province (LLSVP), a structure in the lowermost mantle situated under Africa and adjacent oceans and characterized by low‐shear seismic velocities. According to the interpretation of global and regional tomography models, the CEAA material stalls in the topmost lower mantle, between ∼700 and 1,200 km depth, intermittently generating plumelets under the Central‐East Atlantic. Plate reconstructions from Cenozoic to present confirm that the CEAA is underlying these and other volcanic provinces (e.g., Western Iberia and NW Morocco) since at least 90 Ma. Key Points: The Canary and Madeira hotspots are underlain by distinct upwellings sourced from the lower‐mantle Central‐East Atlantic Anomaly (CEAA)A "vote" analysis of 34 tomography models shows that the CEAA extends vertically from the African LLSVP up to the topmost lower mantleThe plumelets seem at different stages of evolution and rise sporadically from mantle material accumulated below the 660‐km discontinuity [ABSTRACT FROM AUTHOR]

In typical subduction systems, plate convergence is subperpendicular to the trench. The Gibraltar Arc System is exceptional, with its narrow subduction arc oriented N‐S and laterally "squeezed" by the NNW‐SSE tectonic convergence between Nubia and Iberia. The extent to which the slab is still coupled to the surface and how it interacts actively with the surrounding mantle is a matter of ongoing debate. Here, we analyze new densely spaced GPS data, together with crustal and mantle observations, to better understand the slab kinematics, plate dynamics, and mantle flow. In light of previous and current research, we find that subduction below the Gibraltar Arc is currently in the middle of a disruption process, with parts of it already detached and others yet coupled to the surface. In particular, the slab seems to be detached to the north of the Gibraltar Strait, with a small portion still attached to the surface or in the process of detaching below the western Betics. South of Gibraltar, the slab is still coupled to the overriding plate, although the subduction seems to be very slow or stopped. Flow of mantle material around the detached portions of the slab causes most of the surface uplift and a positive residual topography anomaly. Our findings show that the interplay between slab dynamics, mantle flow, and plate convergence explains much of the observed residual topography, surface motion, seismicity, and mantle structure. Key Points: The Gibraltar subduction is undergoing a phase of progressive lateral disruption, with some segments still attached to the surface in the Rif and western BeticsThe slab appears segmented into two domains, one north and the other south of the Gibraltar strait; the segmentation is likely driven by Eurasia‐Nubia convergenceMantle flow around the slab seems still active and causing most of the surface uplift, although the slab is not retreating anymore [ABSTRACT FROM AUTHOR]

Independent models of P wave and S wave velocity anomalies in the mantle derived from seismic tomography help to distinguish thermal signatures from those of partial melt, volatiles, and compositional variations. Here we use seismic data from SW Europe and NW Africa, spanning the region between the Pyrenees and the Canaries, in order to obtain a new S‐SKS relative arrival‐time tomographic model of the upper mantle below Iberia, Western Morocco, and the Canaries. Similar to previous P wave tomographic results, the S wave model provides evidence for (1) subvertical upper‐mantle low‐velocity structures below the Canaries, Atlas Ranges, and Gibraltar Arc, which are interpreted as mantle upwellings fed by a common lower‐mantle source below the Canaries; and (2) two low‐velocity anomalies below the eastern Rif and Betics that we interpret as the result of the interaction between quasi‐toroidal mantle flow induced by the Gibraltar slab and the mantle upwelling behind it. The analysis of teleseismic P wave and S wave arrival‐time residuals and the conversion of the low‐velocity anomalies to temperature variations suggest that the upwellings in the upper mantle below the Canaries, Atlas Ranges, and Gibraltar Arc system may be solely thermal in nature, with temperature excesses in the range ~100–350 °C. Our results also indicate that local partial melting can be present at lithospheric depths, especially below the Atlas Ranges. The locations of thermal mantle upwellings are in good agreement with those of thinned lithosphere, moderate to high heat‐flow measurements, and recent magmatic activity at the surface. Key Points: We present a new high‐resolution teleseismic S wave tomographic model of the upper‐mantle structure below the Ibero‐western Maghrebian regionMantle upwellings below Canaries, Atlas, and Gibraltar arc are sourced in the lower mantle and interact with the retreating Gibraltar slabThe main signature of the mantle upwellings is thermal in nature with temperature excesses of ~100–350 °C [ABSTRACT FROM AUTHOR]

Abstract: Intraplate Iberia is a region of slow lithopsheric deformation (<1 mm/yr) with significant historical earthquake activity. Recent high‐quality instrumental data have shown that small‐magnitude earthquakes collapse along clusters and lineaments, which however do not bear a clear relationship to geologically mapped active structures. In this article, we investigate the controls of these earthquake clusters. In particular, we study two of the identified clusters—the Arraiolos and the Évora seismic zones (ASZ and ESZ), located in the Western Ossa Morena Zone, southwest Iberia. The ASZ marks a sharp boundary between a seismically active region to its south and a more quiet region to its north. We revise historical earthquakes in order to clarify whether earthquake activity in the region is persistent. We use data from a local network to compute accurate epicenters, focal depth, focal mechanisms, and spatiotemporal clustering, thus characterizing ongoing small‐scale fracturing. Finally, we analyze complementary data sets, including tomographic models, Global Navigation Satellite Systems data, magnetic anomalies, and gravity anomalies, in order to discuss the factors that control seismogenesis in the two seismic zones. Consistency between earthquake locations, focal mechanisms and Global Navigation Satellite Systems data suggests that the ASZ is an active right‐lateral shear zone, which divides two blocks within the Western Ossa Morena Zone. The ESZ seems to localize microseismicity due to its granitic lithology. These results suggest that high‐resolution geophysical data have the potential to reveal blocks with different seismogenic and rheological behaviors, which may be used to improve our understanding of fault systems and the assessment of earthquake hazard in slowly deforming regions. [ABSTRACT FROM AUTHOR]

In this paper we present evidence of earthquake dynamic triggering in southeast Africa. We analysed seismic waveforms recorded at 53 broad-band and short-period stations in order to identify possible increases in the rate of microearthquakes and tremor due to the passage of teleseismic waves generated by the Mw8.6 2012 Indian Ocean earthquake. We found evidence of triggered local earthquakes and no evidence of triggered tremor in the region. We assessed the statistical significance of the increase in the number of local earthquakes using ß-statistics. Statistically significant dynamic triggering of local earthquakes was observed at 7 out of the 53 analysed stations. Two of these stations are located in the northeast coast of Madagascar and the other five stations are located in the Kaapvaal Craton, southern Africa. We found no evidence of dynamically triggered seismic activity in stations located near the structures of the East African Rift System. Hydrothermal activity exists close to the stations that recorded dynamic triggering, however, it also exists near the East African Rift System structures where no triggering was observed. Our results suggest that factors other than solely tectonic regime and geothermalism are needed to explain the mechanisms that underlie earthquake triggering. [ABSTRACT FROM AUTHOR]

Seismic ambient noise tomography is applied to central and southern Mozambique, located in the tip of the East African Rift (EAR). The deployment of MOZART seismic network, with a total of 30 broad-band stations continuously recording for 26 months, allowed us to carry out the first tomographic study of the crust under this region, which until now remained largely unexplored at this scale. From cross-correlations extracted from coherent noise we obtained Rayleigh wave group velocity dispersion curves for the period range 5-40 s. These dispersion relations were inverted to produce group velocity maps, and 1-D shear wave velocity profiles at selected points. High group velocities are observed at all periods on the eastern edge of the Kaapvaal and Zimbabwe cratons, in agreement with the findings of previous studies. Further east, a pronounced slow anomaly is observed in central and southern Mozambique, where the rifting between southern Africa and Antarctica created a passive margin in the Mesozoic, and further rifting is currently happening as a result of the southward propagation of the EAR. In this study, we also addressed the question concerning the nature of the crust (continental versus oceanic) in the Mozambique Coastal Plains (MCP), still in debate. Our data do not support previous suggestions that the MCP are floored by oceanic crust since a shallow Moho could not be detected, and we discuss an alternative explanation for its ocean-like magnetic signature. Our velocity maps suggest that the crystalline basement of the Zimbabwe craton may extend further east well into Mozambique underneath the sediment cover, contrary to what is usually assumed, while further south the Kaapval craton passes into slow rifted crust at the Lebombo monocline as expected. The sharp passage from fast crust to slow crust on the northern part of the study area coincides with the seismically active NNE-SSW Urema rift, while further south the Mazenga graben adopts an N-S direction parallel to the eastern limit of the Kaapvaal craton. We conclude that these two extensional structures herald the southward continuation of the EAR, and infer a structural control of the transition between the two types of crust on the ongoing deformation. [ABSTRACT FROM AUTHOR]

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Copyright of Revista de Enfermagem Referência is the property of Escola Superior de Enfermagem de Coimbra and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We present a method to assess the uncertainty of earthquake focal mechanisms based on the standard theory of linear inverse problems. We compute the uncertainty of the moment tensor, M, then map it into uncertainties of the strike, dip, and rake. The inputs are: source and station locations, crustal model, frequency band of interest, and an estimate of data error. The output is a six-dimensional (6D) error ellipsoid, which shows the uncertainty of the individual parameters of M. We focus on the double-couple (DC) part of M. The method is applicable both with and without waveforms. The latter is particularly useful for network design. As an example we present maps of DC resolvability for earthquakes in southwest Europe, computed without waveforms. We find that the resolvability depends critically on frequency range and source depth. Shallow DC sources (10 km) are theoretically better resolved than deeper sources (40 km and 60 km). The DC resolvability of a 40-km-deep event improves considerably when the Portuguese network is supplemented by stations in Spain and Morocco. The DC resolvability can be further improved by using a few ocean bottom seismometer (OBS) stations or a dense land network. A dense land network is able to resolve M well in spite of the large azimuthal gap, which spans ~200°. The theoretical resolution analysis also explains the success of single-station inversions when using a broad frequency range, as exemplified by an application using waveforms of a Mw 6 earthquake offshore Iberia. [ABSTRACT FROM AUTHOR]

An MW 5.9 earthquake occurred beneath the Horseshoe abyssal plain (HAP), offshore southwest Iberia, on 12 February 2007. The region where the earthquake occurred has a high seismogenic and tsunamigenic potential. The purpose of this paper is twofold: (1) to extract information about the source of the earthquake that contributes to the understanding of regional tectonics; and (2) to evaluate the applicability of a fast algorithm to study a moderate earthquake offshore mainland Portugal. We employed the KIWI tools, which implement a multistep inversion algorithm, to infer both the pointand finite-source properties of the earthquake. In order to assess the robustness of our solutions, we performed independent sets of inversions that take different datasets and assumptions (e.g., Green's functions, passbands, wave types) as inputs. We also performed bootstrap analyses in order to appraise the robustness of the source parameters. We concluded that the 2007 HAP earthquake centroid is located at 35.841°N, 10.611°W, at a depth of 39 km. Scalar moment, MO, is consistently retrieved with an average value of 1.00 × 1018 N m (moment magnitude MW 5.9). The finite-fault parameters are difficult to resolve given the existing data. Approximately 70% of our bootstrap solutions indicate a true rupture plane that trends westnorthwest-east-southeast (strike = 128°, dip = 46°, and rake 138°). The location and strike of this fault plane coincide with the southwest Iberian margin (SWIM) faults. However, the 46° dip is difficult to reconcile with the subvertical nature of the SWIM faults. [ABSTRACT FROM AUTHOR]

The 2004 M 6.0 Parkfield earthquake yielded one of the largest amounts of near-source strong ground motion seismic data ever. We invert strong-motion seismograms to obtain a model for the space--time distribution of coseismic slip on the fault. To reduce noise in the inversion, we take into account local amplifications that affect each station by using records of the 1983 M 6.5 Coalinga earthquake. Site amplification correlates well with large peak ground velocities registered during the 2004 Parkfield mainshock. The inversion for a kinematic rupture model yields a nonunique solution: we therefore analyze various rupture models that explain the data equally well. Our preferred rupture model identifies a primary zone of high slip surrounding the hypocenter, where the maximum slip is 57 cm. A secondary slip area. over which contours are not well resolved, is located northwest of the hypocenter. The rupture speed is highly heterogeneous. We infer an average rupture velocity of ∼2.8 km/sec close to the hypocenter, and of ∼3.3 km/sec in the secondary region of large slip to the northwest of the hypocenter. By correlation of our rupture model with both microseismicity and velocity structure, we identify six patches on the fault plane that behave in seismically distinct ways. [ABSTRACT FROM AUTHOR]

ORFEUS (Observatories and Research Facilities for European Seismology; https://www.orfeus-eu.org/) is a collaborative non-profit foundation that promotes seismology in the Euro-Mediterranean area through the collection, archival and distribution of digital seismic waveform data, metadata and derived products. ORFEUS is one of the three pillars of the Thematic Core Service for Seismology within the European Plate Observing System (EPOS Seismology). Hence, all ORFEUS services are developed in coordination with EPOS and are EPOS compliant. Among the goals of ORFEUS are: (a) the development and coordination of waveform data products; (b) the coordination of a European data distribution system, and the support for seismic networks in archiving and exchanging digital seismic waveform data; (c) the encouragement of the adoption of best practices for seismic network operation, data quality control and data management; (d) the promotion of open access to seismic waveform data, products and services for the broader Earth science community. These goals are achieved through the development and maintenance of services targeted to a broad community of seismological data users. Two Service Management Committees (SMCs) are established within ORFEUS devoted to managing, operating and developing (with the support of one or more Infrastructure Development Groups): (i) the European Integrated waveform Data Archive (EIDA; https://www.orfeus-eu.org/data/eida/); and (ii) the European Strong-Motion databases (SM; https://www.orfeus-eu.org/data/strong/). The establishment of two additional SMCs is being considered to represent the computational seismology and mobile pools communities within ORFEUS. Access to ORFEUS EIDA and SM products is ensured through state-of-the-art information and communications technologies, with strong emphasis on federated web services that considerably improve seamless user access to data gathered and/or distributed by ORFEUS institutions. The web services also facilitate the automation of downstream products. Particular attention is paid to adopting clear data policies and licences, and to acknowledging the crucial role played by data providers / owners, who are part of the ORFEUS community. The products and services delivered by ORFEUS are assessed and improved though the technical and scientific feedback of a User Advisory Group, comprised of European Earth scientists with expertise encompassing a broad range of disciplines. This contribution presents the products and services of ORFEUS and introduces the planned key future developments. We welcome community feedback about the ORFEUS strategies aimed at the continuous optimisation of data quality, access, dissemination and use. [ABSTRACT FROM AUTHOR]

We discuss crustal surface velocities in the Gibraltar Arc System derived from around 150 GPS sites in Iberia and Morocco operating between 1995 and 2018. The estimated velocity field shows patterns that are strongly correlated with other geophysical constraints (tomographically imaged velocity anomalies, SKS-splitting, etc.) including seismicity patterns. Broad-scale surface uplift characterizes the Rif-Betics belts, which appear underlain by seismically slow, presumably relatively hot, mantle. Significant rates of subsidence are observed around Cartagena and east of El Hoceima where high-velocity seismic anomalies are imaged in the mantle. This abrupt change of the sign of vertical crustal motions coincides with the location of the Trans-Alboran Shear Zone (TASZ), which is marked by lineaments of mostly strike-slip and trans-tensional shallow earthquakes. We interpret the surface uplift as result of the quasi-toroidal mantle flow induced by the interaction of the retreating Gibraltar slab and the resulting sub-slab upwelling. The part of the Gibraltar slab that is still attached to the crust imaged east of the TASZ may contribute to the observed subsidence rates. The trend of the residual topography also suggests that topography may be controlled in part by mantle-driven processes. Around the Gibraltar slab the contrasting signal between the negative residual topography and positive vertical GNSS data is likely due to the fact that the surface, which was previously depressed by the load of the subduction, is now isostatically recovering. Our results on the Gibraltar Arc System suggest that both surface deformation along the arc and shallow earthquake activity are strongly controlled by coupling between the lithosphere and underlying mantle dynamics. [ABSTRACT FROM AUTHOR]

The Gloria fault is a major strike-slip oceanic plate boundary fault, which links the Azores triple junction, in the west, to the oblique convergent boundary between Iberia and NW Africa, in the east. This fault hosted some of the largest strike-slip earthquakes in the oceanic domain, notably the 1941 M8.3 earthquake. In 1975, a M8.1 earthquake hit the intraplate region south of the Gloria fault, in the intersection between an old transform fault and the Madeira-Tore rise. In spite of its seismo-tectonic relevance, the Gloria fault has remained poorly studied, due mostly to its remote location in the north Atlantic.The dataset of the Deep Ocean Test Array (DOCTAR) project encompasses data collected for 10 months at 12 broadband (60-sec) ocean bottom seismometers (OBSs) located about 100 km north of the Gloria fault. This dataset was used to image crustal and mantle discontinuities using receiver function analysis and to infer the S-wave velocity structure of the oceanic lithosphere north of the Gloria fault from P-wave polarization. The seismic structure studies indicate a typical oceanic crustal and mantle structure, influenced by the nearby Gloria fault. In particular, these studies indicate a slight crustal thickening towards the Gloria fault, as well as an increase in uppermost mantle S-wave velocities towards the fault.In this work, we further explore the crustal and uppermost mantle oceanic structure North of the Gloria fault by applying the techniques of ambient noise tomography. We extracted the empirical Green's functions from ambient noise phase cross-correlation (Schimmel et al., 2011), followed by time-frequency phase weighted stack (Schimmel et al., 2007) of continuous seismic and hydrophone data recorded at the array. Our results indicate that the EGFs have a higher signal-to-noise ratio when they are computed from hydrophone-hydrophone or hydrophone-vertical channel data. Pairs of stations oriented NE-SW, show a much highly symmetric cross-correlation on both sides. In HH, HZ, ZH, and ZZ, the record sections highlight a move-out velocity of 1.3 km/s while in the RR and TT shows two different waves with velocities of ~1.3 and 3.2 km/s, respectively. Observed dispersion curves of group velocity over the period range 2 – 25 sec show almost a constant velocity until 15 seconds. After 15 s, we do not obtain reliable dispersion measurements. We compared our results with synthetics computed using a local velocity model, which results from the combination of two different velocity models proposed for the region, and locating the source at 1 m depth in the sediments. The synthetics thus obtained show a good agreement with our observations, suggesting that an ambient noise tomography can be computed from this ocean bottom dataset.The authors acknowledge support from the Portuguese FCT – Fundação para a Ciência e a Tecnologia, I.P., within the scope of project UTAP-EXPL/EAC/0056/2017 and with the FCT grant PD/BD/135069/2017. [ABSTRACT FROM AUTHOR]

Fifty years ago, on 28 February 1969, at 3:41 local time, an earthquake located offshore SW Iberia strongly shook all the south of Portugal. Maximum intensities of VIII were recorded in the SW tip of Portugal, with intensities VII widespread in the south of Portugal and north of Lisbon. The earthquake was felt up to 1300 km from the epicenter, particularly in Bordeaux, France, and in the Canaries, north Atlantic. With an estimated magnitude of Ms 7.9, this event is currently the highest magnitude felt earthquake in the European historical catalog. One WWSSN seismic station operated in Portugal at the time, in Oporto, while another two seismic observatories (Lisbon and Coimbra) also recorded the earthquake. One strong-motion accelerometer located in the 25th of April bridge, which links Lisbon to the southern margin of the Tagus river, provided the closest non-clipped record of the earthquake. The earthquake occurred at a time when Plate Tectonics was just developing. According to studies carried out in the 70s and 80s, the earthquake, with epicenter in the middle of the Horseshoe Abyssal Plain, had a depth of 22-33 km, Ms 7.9, and the focal mechanism indicates reverse faulting, on a fault striking NE-SW (40 to 70 degrees), a dip of ~50 deg, with a small component of left-lateral faulting. Current microseismic studies indicate that earthquakes in this region frequently occur at depths of ~40 km, indicating brittle failure in the lithospheric mantle, which has classically been attributed to the old and cold nature of the lithosphere in the region. The relationship between instrumental seismicity, historical earthquakes, geologically mapped faults, Earth structure and rheology in this region, which acts as a diffuse plate boundary between the EU and AF plates, and which may have also unleashed the great 1755 Lisbon earthquake, remains enigmatic until today.Taking advantage of the 50th anniversary of this earthquake, of the fact that many citizens still remember well this impressive earthquake, and of currently available technology, a collaborative enterprise between seismologists and engineers, from academic institutions and from the Portuguese seismic network, is launching a Did You Feel It (DYFI) questionnaire for citizens to report back on felt and observed effects of this landmark earthquake that occurred 50 years ago. The resulting macroseismic information will be analyzed with a particular focus on regional attenuation, site effects, and social response of the population. In this presentation, we will review main aspects of this earthquake and report on the first results of the DYFI questionnaire.The authors acknowledge support from the Portuguese FCT – Fundação para a Ciência e a Tecnologia, I.P., within the scope of project SPIDER PTDC/GEO-FIQ/2590/2014 and Instituto Dom Luiz UID/GEO/50019/2019. [ABSTRACT FROM AUTHOR]

The article reviews the book "Natural Disasters," by Patrick L. Abbott.

Upper-mantle upwellings are often invoked as the cause of Cenozoic volcanism in the Ibero-western Maghreb region. However, their nature, geometry and origin are unclear. This study takes advantage of dense seismic networks, which cover an area extending from the Pyrenees in the north to the Canaries in the south, to provide a new high-resolution P -wave velocity model of the upper-mantle and topmost lower-mantle structure. Our images show three subvertical upper-mantle upwellings below the Canaries, the Atlas Ranges and the Gibraltar Arc, which appear to be rooted beneath the upper-mantle transition zone ( MTZ ). Two other mantle upwellings beneath the eastern Rif and eastern Betics surround the Gibraltar subduction zone. We propose a new geodynamic model in which narrow upper-mantle upwellings below the Canaries, the Atlas Ranges and the Gibraltar Arc rise from a laterally-propagating layer of material below the MTZ , which in turn is fed by a common deep source below the Canaries. In the Gibraltar region, the deeply rooted upwelling interacts with the Gibraltar slab. Quasi-toroidal flow driven by slab rollback induces the hot mantle material to flow around the slab, creating the two low-velocity anomalies below the eastern Betics and eastern Rif. Our results suggest that the Central Atlantic plume is a likely source of hot mantle material for upper-mantle upwellings in the Ibero-western Maghreb region. [ABSTRACT FROM AUTHOR]

A correction to the article "Kinematic Inversion of the 2004 M 6.0 Parkfield Earthquake Including an Approximation to Site Effects" that was published in a previous issue is presented.