Fault slip rate is one of the most crucial parameters to characterize earthquake occurrence in fault‐based seismic hazard assessments (SHA). Accordingly, paleoseismic studies have increasingly ...focused on constraining this parameter in active faults worldwide. We present a comprehensive paleoseismic study in the Alhama de Murcia Fault (AMF), one of the most active faults in SE Spain and source of destructing earthquakes such as the 2011 Mw 5.2 Lorca event. Contrasting with previous studies, we integrate paleoseismic data from four fault strands in the AMF and, based on trench slip analysis and numerical dates, we derive slip rate estimates of each strand over the whole transect and assess their time variability. The AMF has a minimum net slip rate between 1.35+0.16/−0.10 and 1.64+0.16/−0.11 mm/yr for the past 18 ± 1 to 15.2 ± 1.1 ka. These results prove the importance of accounting for the complete sections of a geological structure as they are almost twice the previous estimates for a single fault branch. Slip rate variability is identified in the AMF, with cyclic acceleration‐quiescence patterns that could be related to stress field changes driven by fault interaction or synchronicity with neighboring faults (e.g., Carrascoy). We hope that the data presented here motivates their inclusion into forthcoming fault‐based SHAs. In this regard, limitations related to the lack of paleoseismic data for one fault strand, along with poor characterization of the strike component of slip and insufficient age control of the units for another strand are highlighted and need to be accounted for by modelers.
Key Points
Multi‐site paleoseismic surveys allow to improve the estimations of the geological slip rates in the Alhama de Murcia Fault (AMF)
The AMF shows a geological slip rate between 1.35 and 1.64 mm/yr for the past 18–15 ka
Late Quaternary slip rate fluctuations suggest strain rate variations and highlight possible synchronicities with neighboring faults
Complete rupture of the Padul Fault represents one of the largest plausible earthquakes in the Sierra Nevada Range, one of the most seismically active regions of Spain. We performed a regional ...assessment of earthquake-triggered slope instabilities in the western part of the range to determine the most likely types of failures from such an earthquake in the region and suggest where such failures have a higher likelihood of occurring. These results are broadly useful for management of regional life-lines and future development. First, a slope-instability inventory of the Sierra Nevada was produced to identify the most common instability types. Subsequently, the Newmark’s sliding rigid-block methodology, implemented in a geographic information system, was used to obtain the distribution of Newmark displacements in the area considering a M w 6.6 earthquake on the Padul Fault. The Newmark displacements were then compared to the distribution of the inventoried slope instabilities to identify the areas where seismicity could reactivate old slope instabilities or generate new ones, and to identify the involved landslide typology. The most likely seismically induced slope instabilities in the Sierra Nevada are rock falls and rock slides. These types of instabilities could be triggered by Newmark displacements of 2 cm or less.
The state of Chiapas (SE México) conforms a territory of complex tectonics and high seismic activity. The interaction among the Cocos, North American and Caribbean tectonic plates, as well as the ...active crustal deformation inside Chiapas, determines a variety of seismogenic sources of distinct characteristics and particular strong ground motion attenuation. This situation makes the assessment of seismic hazard in the region a challenging task. In this work, we follow the methodology of probabilistic seismic hazard analysis, starting from the compilation of an earthquake catalogue, and the definition of seismogenic source-zones based on the particular seismotectonics of the region: plate-subduction-related sources (interface and intraslab zones), active crustal deformation zones and the shear zone between the North American and Caribbean plates formed by the Motagua, Polochic and Ixcán faults. The latter source is modelled in two different configurations: one single source-zone and three distinct ones. We select three ground motion prediction equations (GMPEs) recommended for South and Central America, plus two Mexican ones. We combine the GMPEs with the source-zone models in a logic tree scheme and produce hazard maps in terms of peak ground acceleration and spectral acceleration for the 500-, 1000- and 2500-year return periods, as well as uniform hazard spectra for the towns of Tuxtla Gutiérrez, Tapachula and San Cristóbal. We obtain higher values in comparison with previous seismic hazard studies and particularly much higher than the output of the Prodisis v.2.3 software for seismic design in México. Our results are consistent with those of neighbouring Guatemala obtained in a recent study for Central America.
This work summarises the seismic hazard analysis performed for the complete characterisation of strong ground-motion at the site of the Itoiz dam (Western Pyrenees, Spain). The hazard analysis ...includes the compilation of a composite catalogue from French and Spanish agencies, the definition of an original hybrid seismogenic source model (including zones and major faults) and the selection of ground motion prediction equations (GMPEs). Hazard results are provided as hazard curves and acceleration response spectra on rock for the 1000- and 5000-year return periods, which correspond respectively to the operating basis earthquake (OBE) and safety evaluation earthquake (SEE). The impact of truncating GMPEs at a number of standard deviations (epsilon) has been found not critical here for the return periods targeted. Subsequently, an analysis of the contribution of each source to total hazard and a hazard disaggregation analysis are performed in order to establish the earthquake-source parameters for both the OBE and SEE scenarios consistently with the seismotectonics of the region. The European Strong Motion database is then searched and a selection of records is proposed for each of the scenarios. Our results suggest that seismic hazard in the region is underestimated by the official Spanish seismic hazard map included in the current version of the code (NCSE-02), which is the reference document for the definition of seismic actions for dam projects in the whole Pyrenees.
A probabilistic seismic hazard assessment of the Province of Murcia in terms of peak ground acceleration (PGA) and spectral accelerations SA(T) is presented in this paper. In contrast to most of the ...previous studies in the region, which were performed for PGA making use of intensity-to-PGA relationships, hazard is here calculated in terms of magnitude and using European spectral ground-motion models. Moreover, we have considered the most important faults in the region as specific seismic sources, and also comprehensively reviewed the earthquake catalogue. Hazard calculations are performed following the Probabilistic Seismic Hazard Assessment (PSHA) methodology using a logic tree, which accounts for three different seismic source zonings and three different ground-motion models. Hazard maps in terms of PGA and SA(0.1, 0.2, 0.5, 1.0 and 2.0 s) and coefficient of variation (COV) for the 475-year return period are shown. Subsequent analysis is focused on three sites of the province, namely, the cities of Murcia, Lorca and Cartagena, which are important industrial and tourism centres. Results at these sites have been analysed to evaluate the influence of the different input options. The most important factor affecting the results is the choice of the attenuation relationship, whereas the influence of the selected seismic source zonings appears strongly site dependant. Finally, we have performed an analysis of source contribution to hazard at each of these cities to provide preliminary guidance in devising specific risk scenarios. We have found that local source zones control the hazard for PGA and SA(T≤1.0 s), although contribution from specific fault sources and long-distance north Algerian sources becomes significant from SA(0.5 s) onwards.PUBLICATION ABSTRACT
During the 2000 and 2001 R/V Cornide de Saavedra cruises a vast field of hydrocarbon-derived carbonate chimneys was discovered and sampled along the Cádiz Contourite Channel and Guadalquivir Diapiric ...Ridge. Photographs taken on board using an underwater camera revealed a spectacularly high density of pipe-like chimneys lying on the sea floor, though some of them were also found protruding from muddy sediment. The major axes of the fallen chimneys, which can be as long as 1
m, exhibit a regular spatial distribution showing a conspicuous NW-SE trend. Furthermore, their basal morphology shows a characteristic angular breakage associated to a flexo-traction process. Both the uniform distribution of the major axis and the basal morphology of the chimneys imply that the cause of the rupture could be related either to strong bottom sea currents or to inertia forces associated with oscillatory ground motion due to seismic shaking. The preferential orientation of the broken chimneys, their mechanical properties, the geological and topographical conditions of the area in relation to seismic ground motion amplification and the flow speed of the Mediterranean Outflow Water (MOW) along the Cádiz Contourite Channel, suggest that the most probable cause of the chimneys’ rupture was an earthquake. The minimum magnitude of this seismic event is estimated to be more than 7.0, the causative fault being located directly under the chimney field or as far as 30–60
km away. The chimneys’ rupture took place between ca 5
ka to Present.
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