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Universitat de Barcelona, Spain
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- PublicationOpen AccessEvidence for past earthquakes in an area of low historical seismicity: the Catalan coastal ranges, NE Spain(1996-05)
; ;Masana, E.; Departament de Geologia Dinàmica, Geofisica i Paleontologia, Universitat de Barcelona, SpainThe Catalan coastal ranges are situated far away from a plate margin and thus are characterised by low rates of deformation and low seismicity. Nevertheless, up to six morphological scarps in quaternary alluvial fans, large landslides and liquefaction features were detected in the southern half of these ranges and motivated a more detailed geomorphologic and palaeoseismologic study. In the Baix Ebre Fault zone, the morphological analysis of the mountain front and the fluvial network showed evidence of alternative periods of uplift and quiescence and suggested a sub-actual reactivation of the fault after a recent stable period. In El Camp zone the Almadrava andMont-roig scarps were analysed in detail. The first shows evidence of fault control and of two probably seismic deformation events. A normal semi-hidden fault that folds the surface was suggested to explain the deformation observed in this scarp. The second is also considered to be controlled by a fault which was active between 100000 and 4490-4790 year B.C. If creep deformation could be rejected the Mont-roig scarp fault may be considered an active fault able to generate large earthquakes (M > 6.5). In summary, although the zone shows low historical seismicity, evidence that can be referred to past earthquakes was detected. Further palaeoseismologic studies should be carried out in these structures in order to better constrain the active behaviour of the faults.213 522 - PublicationOpen AccessEffects of repeated paleoearthquakes on the Alhama de Murcia Fault (Betic Cordillera, Spain) on the Quaternary evolution of an alluvial fan system(2003)
; ; ; ; ;Martínez-Díaz, J. J.; Departamento de Geodinámica, Universidad Complutense de Madrid, Spain ;Masana, E.; Departamento de Geologia Dinàmica i Geofísica, Universitat de Barcelona, Spain ;Hernández-Enrile, J. L.; Departamento de Geodinámica, Universidad Complutense de Madrid, Spain ;Santanach, P.; Departamento de Geologia Dinàmica i Geofísica, Universitat de Barcelona, Spain; ; ; In this work we present a study of an alluvial fan system, which is affected by the Quaternary activity of the leftlateral, reverse Alhama de Murcia Fault (Betic Cordillera). Paleoseismic studies in this area yield data that can be compared and correlated with the morphologic and tectono-sedimentary evolution of the alluvial fan. The spatial arrangement of the sedimentary alluvial fan units near the fault zone, shown in trenches, is controlled by the recurrent reverse, left-lateral coseismic events. We analysed the morphology of the drainage network using a 1:5000 scale orthoimage to identify and measure horizontal deflections along the fault. The channel pattern analysis allowed us to estimate the average horizontal slip rate of the SAMF for the last 130 ka. This value is 0.21 mm/a, which is slightly higher than the range of values obtained by trenching analysis for the last 30 ka, (0.06 to 0.15 mm/yr). The interpretation of the stratigraphic sequence exposed along the trench walls constrained the occurrence of at least two surface faulting earthquakes during the last 30000 years. The most recent event happened after the El Saltador Creek dissected the alluvial fan. The penultimate event occurred while the alluvial fan was still active.910 357 - PublicationRestrictedPaleoseismicity of the 1981 Corinth earthquake fault: Seismic contribution to extensional strain in central Greece and implications for seismic hazard(1998-12-10)
; ; ; ; ; ; ;Collier, R. E. L.; Department of Earth Sciences, University of Leeds, Leeds, England, United Kingdom ;Pantosti, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;D'Addezio, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;De Martini, P. M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Masana, E.; 3Departament de Geologia Dinàmica, Geofísica i Paleontologia, Universitat de Barcelona, Barcelona, Spain ;Sakellariou, D.; National Centre for Marine Research, Agios Kosmas, Hellenikon, Athens, Greece; ; ; ; ; We present paleoseismological trenching results for the active Skinos Fault, which ruptured the surface on the Alkyonides Gulf basin margin in the 1981 Gulf of Corinth earthquake sequence. Three trenches expose evidence of up to six previous events which are comparable to the 1981 deformation in terms of size and geometry. Vertical displacement produced by the 1981 earthquake ranged from 0.45 to 1.3 m at the Bambakies Fan trench sites, decreasing towards the eastern fault tip east of the trenches. Trench 1 reveals two previous events with vertical displacements between 0.5 and 1.2 m since 390 A.D. Trench 2 reveals five or six previous events, but these are not dated. Trench 3 reveals four previous events since 670 A.D. Vertical displacements associated with interpreted paleoearthquakes at the trench sites are ≤1.2 m. The recurrence interval on the Skinos Fault is estimated to average 330 years. However, significant variation in recurrence interval is allowed by the available radiometric dates. Average vertical displacement rates derived from the trenches are in the range 0.7-2.5 mm/yr. A similar long-term average vertical displacement rate of 1.2-2.3 mm/yr is estimated for the lifespan of the basin-bounding fault. This equates to a horizontal seismic strain contribution of ≤2.5 mm/yr from the Skinos Fault. This local seismic strain rate overlaps, within error, with geodetically determined velocities across the Alkyonides Gulf assumed to represent uniform deep-crustal strain. Thus seismic deformation on the basin-bounding fault system may take up the major part of extension across the basin, and aseismic strain is not necessitated by the data. If correct, this would imply that geodetically determined strain rates may be used as a proxy for potential seismic moment release in seismic hazard analyses for this region.191 27 - PublicationOpen AccessActive tectonics around the Mediterranean region: site studies andMore than 25 years have passed since the definition of Active Tectonics as "tectonic movements that are expected to occur within a future time span of concern to society", formulated in a milestone book by the National Research Council on this topic (Studies in Geophysics, Active Tectonics, National Academy Press, Washington, D.C. 1986), and those words have still to be considered the most suitable and exhaustive way to explain this branch of the Earth Sciences. Indeed only bridging together basic studies ("tectonic movements"), rates of occurrence ("time span") and hazard assessment ("society") can we fully evaluate ongoing tectonic activity and its associated hazards. The broad Mediterranean Sea region is a paradigmatic area from this point of view, as on one hand this region displays in a relatively limited geographic extent a great variety of tectonic processes such as plate collision, subduction, volcanic activity, large-magnitude earthquakes, active folding and faulting, vertical uplift and/or subsidence. On the other hand, all the above mentioned tectonic processes can potentially affect a total population of about 450 million, mostly concentrated in fast-growing urban areas and/or close to industrial compounds and critical facilities often located nearby hazard sources.
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