Contribution of active faults in the intraplate area of Iberia to seismic hazard: The Alentejo-Plasencia Fault

Villamor, Pilar; Capote, Ramón; Stirling, Mark; Tsigé, Meaza; Berryman, Kelvin; Martínez‐Díaz, J. J.; Martín-González, Fidel

doi:10.5209/rev_jige.2012.v38.n1.39207

Cited by 25 publications

(14 citation statements)

References 18 publications

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“…Of all these faults, only the Lower Tagus Valley and Vidigueira-Moura faults have been convincingly documented as potentially active (Basili et al, 2013;Canora et al, 2015;da Silveira et al, 2009). The Messejana fault (also known as Alentejo-Plasencia or Odemira-Ávila) is a major tectonic structure of Iberia, whose geomorphology suggests left-lateral strike-slip motion (e.g., Villamor et al, 2012). It is still debated whether the fault is currently active, and if so, along which segments (Basili et al, 2013;Villamor et al, 2012).…”

Section: Seismotectonic Framework and Geological Inheritancementioning

confidence: 99%

“…The Messejana fault (also known as Alentejo-Plasencia or Odemira-Ávila) is a major tectonic structure of Iberia, whose geomorphology suggests left-lateral strike-slip motion (e.g., Villamor et al, 2012). It is still debated whether the fault is currently active, and if so, along which segments (Basili et al, 2013;Villamor et al, 2012). Interestingly, in our study region, the Messejana fault seems to separate a region of lower seismic activity, to its SE, from a region of higher seismic activity, to its NW.…”

Section: Seismotectonic Framework and Geological Inheritancementioning

confidence: 99%

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An Active Seismic Zone in Intraplate West Iberia Inferred From High‐Resolution Geophysical Data

et al. 2018

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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.

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Section: Seismotectonic Framework and Geological Inheritancementioning

confidence: 99%

Section: Seismotectonic Framework and Geological Inheritancementioning

confidence: 99%

An Active Seismic Zone in Intraplate West Iberia Inferred From High‐Resolution Geophysical Data

et al. 2018

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“…[2] also suggest that seismotectonic activity in western Iberia could not account for the Iberia-Eurasia relative motion predicted by [4]. However, recent works [52] confirm that such zone is dissected by a number of active NNE-striking faults, whose slip rates could reach 0.8 mm/yr, which roughly matches the amplitude of the Iberia-Eurasia relative motion predicted by [4]. In our opinion, the fact that both the boundary zones between the presumed Iberia plate and Eurasia are affected by significant seismicity (Figure 4) cannot easily be reconciled with a null relative motion between such plates.…”

Section: Southern Adria Kinematics and Nubia-eurasia Relative Motionmentioning

confidence: 99%

Present Velocity Field in the Italian Region by GPS Data: Geodynamic/Tectonic Implications

Mantovani

Viti

Cenni³

et al. 2015

IJG

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The analysis of geodetic observations carried out by 478 continuous GPS stations in the Italian region\ud since 2001 has allowed a fairly good definition of the ongoing horizontal velocity field with\ud respect to Eurasia. It is argued that such evidence can provide important insights into the geodynamic\ud context in the central Mediterranean area. Numerous velocity vectors in the Apulia zone\ud coherently indicate that the southern Adriatic domain is moving roughly NE ward. Since no significant\ud decoupling zone between this domain and Nubia has so far been recognized, one could\ud expect that the kinematics of these two plates is compatible. However, this condition is not fulfilled\ud if the Nubia-Eurasia relative motion is taken from the global kinematic models, either deduced\ud by long-term evidence [1] or short-term geodetic data [2] [3]. This problem is considerably\ud reduced if the alternative Nubia-Eurasia rotation pole suggested by [4] is taken into account. This\ud choice is also suggested by other major long-term evidence in the Mediterranean region. The numerous\ud geodetic vectors available in two Adriatic sectors, the Apulia zone and the Venetian plain,\ud would imply an Adria-Eurasia rotation pole incompatible with all Nubia-Eurasia Eulerian poles so\ud far proposed. Since a significant relative motion between these plates is not compatible with the\ud absence of a tectonic decoupling zone, we suppose that the short-term kinematics of Adria might\ud be influenced by a transient non-rigid behaviour of that plate. This hypothesis is compatible with\ud the expected effects (post seismic relaxation) of the major decoupling earthquakes that have occurred\ud along Periadriatic zones in the past tens of years. The compatibility of the GPS kinematic\ud pattern in the Apennine belt, Calabria Arc and Sicily with the implications of the geodynamic/tectonic\ud interpretations so far proposed for the central Mediterranean area is then discussed

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“…However, given the wide uncertainties on earthquake ages, and the structure of the fault system, any correlation with canyon-flushing events would be largely speculative. There are multiple other intraplate faults that may trigger canyon-flushing, but without accurate paleoseismic records it is impossible to imply causation (Buforn et al, 1988;Zitellini et al, 2004;Villamor et al, 2012;Custódio et al, 2015). The lack of convincing evidence for earthquake triggered canyon-flushing along this margin highlights the problems of applying turbidite paleoseismology methods to structurally complex margins.…”

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confidence: 99%

Different frequencies and triggers of canyon filling and flushing events in Nazaré Canyon, offshore Portugal

Allin¹,

Talling²,

Clare³

et al. 2017

Preprint

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Submarine canyons are one of the most important pathways for sediment transport into ocean basins. For this reason, understanding canyon architecture and sedimentary processes has importance for sediment budgets, carbon cycling, and geohazard assessment. Despite increasing knowledge of turbidity current triggers, the down-canyon variability in turbidity current frequency within most canyon systems is not well constrained.NewAMS radiocarbon chronologies from canyon sediment cores illustrate significant variability in turbidity current frequency within Nazaré Canyon through time. Generalised linear models and Cox proportional hazardsmodels indicate a strong influence of global sea level on the frequency of turbidity currents that fill the canyon.Radiocarbon ages from basin sediment cores indicate that larger, canyon-flushing turbidity currents reachingthe Iberian Abyssal Plain have a significantly longer average recurrence interval than turbidity currents that fillthe canyon. The recurrence intervals of these canyon-flushing turbidity currents also appear to be unaffectedby long-term changes in global sea level. Furthermore, canyon-flushing and canyon-filling have very differentstatistical distributions of recurrence intervals. This indicates that the factors triggering, and thus controllingthe frequency of canyon-flushing and canyon-filling events are very different. Canyon-filling appears to be predominantly triggered by sediment instability during sea level lowstand, and by storm and nepheloid transportduring the present day highstand. Canyon-flushing exhibits time-independent behaviour. This indicates that atemporally random process, signal shredding, or summation of non-random processes that cannot be discerned from a random signal, are triggering canyon flushing events.

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Contribution of active faults in the intraplate area of Iberia to seismic hazard: The Alentejo-Plasencia Fault

Cited by 25 publications

References 18 publications

An Active Seismic Zone in Intraplate West Iberia Inferred From High‐Resolution Geophysical Data

An Active Seismic Zone in Intraplate West Iberia Inferred From High‐Resolution Geophysical Data

Present Velocity Field in the Italian Region by GPS Data: Geodynamic/Tectonic Implications

Different frequencies and triggers of canyon filling and flushing events in Nazaré Canyon, offshore Portugal

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