Approach to the Lower Pliocene marine-continental correlation from southern Spain. The micrommamal site of Alhaurín el Grande-1 (Málaga Basin, Betic Cordillera, Spain)

A new micromammal site at Alhaurín el Grande (Málaga, southern Spain) located above early Pliocene marine deposits allows an approach to the marine-continental correlation for this age. The early Pliocene marine filling throughout the Málaga Basin is developed in three transgressive-regressive sequences (Pl-1, Pl-2, and Pl-3 units) bounded by discontinuities. At the top of the intermediate sequence Pl-2, peaty sediments have yielded fossils of Rodentia, Lagomorpha, Insectivora, and Crocodylia. The presence of Cricetus barrieri Mein & Michaux, 1970 in combination with murids, both of primitive morphology, such as Apodemus gudrunae Van de Weerd, 1976, and more advanced forms (i.e. Occitanomys brailloni Michaux, 1969 and Stephanomys donnezani cordii Ruiz Bustos, 1986), points to an early Ruscinian age (MN 14 biozone). Based on the planktonic foraminifers, the biostratigraphic data indicate that marine sediments just below the micromammal beds belong to the MPl-2 biozone of the early Zanclean. Available paleomagnetic data from the marine sediments show that the micromammal bed must be located between the normal geomagnetic subchron C3n3n (4.89-4.80 Ma) and the subchron C3n2n (4.63-4.49 Ma), limiting the age of this site to the late part of the early Zanclean

Paleoseismological evidence of Holocene activity of the Los Tollos Fault (Murcia, SE Spain): A lately formed Quaternary tectonic feature of the Eastern Betic Shear Zone

The Los Tollos Fault is a recent and important feature of the Eastern Betic Shear Zone, one of the major tectonic structures in South Iberia accommodating the convergence between Nubian and Eurasian plates in the western Mediterranean. The Los Tollos Fault became active by the end of Middle Pleistocene introducing some paleogeographical modifications. Previously mapped as a secondary normal fault related to the Carrascoy Fault, recent research evidences that the Los Tollos Fault is an independent Holocene active left-lateral reverse fault extending for at least 15 km. Data analysis from 4 trenches dug across the fault has revealed the occurrence of at least two paleo-earthquake events during the Holocene. The most recent event is dated between 2,740 and 2,140 yr BP (8th to 2nd centuries BC). The size of the paleoevents is calculated to be Mw 6.3 – 6.6 following empirical regressions on surface rupture length. The recurrence interval is estimated to be between 2,200-6,860 years, fitting a slip rate for the fault between 0.12 and 0.17 mm/yr. Such parameters highlight the Los Tollos Fault as a tectonic structure with a considerable activity located relatively close to densely populated areas. These seismogenic parameters should be considered in future reassessments of the seismic hazard of the region.La falla de Los Tollos es una estructura reciente e importante de la Zona de Cizalla de la Bética Oriental, la principal estructura del sureste de la Península Ibérica que acomoda gran parte de la convergencia entre las placas de Eurasia y Nubia en el Mediterráneo Occidental. La falla de Los Tollos, descrita inicialmente como una falla normal secundaria relacionada con la falla de Carrascoy, comenzó su actividad a finales del Pleistoceno Medio generando algunas modificaciones paleogeográficas significativas. El trabajo que aquí presentamos demuestra su activad durante el Holoceno con una cinemática lateral sinestral con componente inversa a lo largo de una longitud de 15 km, e independiente de la Falla de Carrascoy. Del análisis de los datos obtenidos en 4 trincheras paleosismológicas realizadas a lo largo de la traza de la falla, se han podido interpretar la ocurrencia de al menos 2 paleoterremotos durante el Holoceno, acotándose el evento más reciente entre hace 2.740 y 2.140 años (siglos VIII a II a.C.). La magnitud máxima de estos paleoterremotos, estimada mediante correlaciones empíricas que consideran la longitud de rotura en superficie de la falla, se encuentra entre Mw 6,3 y 6,6, con un periodo de recurrencia comprendido entre 2.200 y 6.860 años. La tasa de deslizamiento neta calculada para la falla se estima entre 0,12 y 0,17 mm/a. Estos parámetros identifican la falla de Los Tollos como una estructura activa situada en las cercanías de áreas densamente pobladas y ponen de manifiesto el interés que tendría considerarla en futuras reevaluaciones de la peligrosidad sísmica en la región

Primeros resultados sobre la aplicación de la técnica de racemización de aminoácidos en la Región de Murcia (SE de la Península Ibérica) y su interés en estudios de paleosismología

Geochronology is a critical issue in paleoseismological research. The aminoacid racemization technique shows important advantages respect to more traditional dating methods; not just for the lower costs and promptness, also because the object to analyze is relatively frequent, in this study: terrestrial gastropods. Furthermore, the costs of the analysis are by far faster and cheaper compared to other dating techniques. Racemization results allow comparing the relative age from different sedimentary units from one trench to another.Additionally, the racemization technique can also be used as a geochronological tool, provided a calibration curve has been first obtained for the particular climate for the area and, ideally, for a particular genus. In this study we show the results obtained from the analysis of 40 samples of terrestrial gastropods from 7 different trenches located in the Murcia Region (SE Spain). Making use of the D/L ratio of aspartic acid we show the coherence found between relative stratigraphic ages and the racemization age. Finally, we show a provisional conversion equation between age of racemization, obtained from Torres et al. (1997) algorithm, and the likely age of the samples. RESUMEN: El control geocronológico es una cuestión crítica en los estudios de paleosismología. La técnica de racemización de aminoácidos ofrece importantes ventajas respecto a otros métodos de datación, tanto en los costes y rapidez, como en la facilidad de encontrar el objeto de análisis; en este estudio, gasterópodos terrestres. Los resultados permiten comparar la edad relativa entre unidades sedimentarias diferentes de unas zanjas a otras. La técnica de racemización también es una herramienta geocronológica, si bien es necesario primero establecer una curva de calibración para el ambiente climático de la zona e, idealmente, para un género concreto. En este estudio se muestran los resultados obtenidos en 40 muestras de gasterópodos terrestres recogidas en 7 zanjas de investigación paleosismológica en la Región de Murcia. Haciendo uso de la relación D/L del ácido aspártico mostramos la coherencia entre las edades relativas estratigráficas y su edad de racemización. Finalmente, proponemos una relación provisional de conversión entre las edades de racemización obtenidas por el algoritmo de Torres et al. (1997) para gasterópodos de la zona central de la Península Ibérica y la edad probable de las muestras

Active fault databases: building a bridge between earthquake geologists and seismic hazard practitioners, the case of the QAFI v.3 database

Abstract. Active fault databases are a very powerful and useful tool in seismic hazard assessment, particularly when singular faults are considered as seismogenic sources. Active fault databases are also a very relevant source of information for earth scientists, earthquake engineers and even teachers or journalists. Active fault databases, hence, should be updated and through reviewed on a regular basis in order to keep a standard quality and uniformed criteria. Desirably, active fault databases should indicate somehow the quality of the geological data and, particularly, the reliability attributed to crucial fault-seismic parameters, as Maximum Magnitude and Recurrence Interval. In this paper we explain how we tackled these issues during the process of updating and reviewing the Quaternary Active Fault Database of Iberia (QAFI) to its current version 3. We devote particular attention to describing the scheme devised for classifying the quality and representativeness of the geological evidence of Quaternary activity and the accuracy of the slip rate estimation in the database. Subsequently, we use this information as input for a straightforward rating of the level of reliability of Maximum Magnitude and Recurrence Interval fault seismic parameters. We conclude that QAFI v.3 is a much better database than version 2 either for a proper use in seismic hazard applications or as an informative source for non-specialized users. However, we already envision new improvements for a future update. </jats:p

La Base de Datos de Fallas Activas en el Cuaternario de Iberia (QAFI v.2.0)

ABSTRACT. The Quaternary Active Faults Database of Iberia (QAFI) is an initiative lead by the Institute of Geology and Mines of Spain (IGME) for building a public repository of scientific data regarding faults having documented activity during the last 2.59 Ma (Quaternary). QAFI also addresses a need to transfer geologic knowledge to practitioners of seismic hazard and risk in Iberia by identifying and characterizing seismogenic fault-sources. QAFI is populated by the information freely provided by more than 40 Earth science researchers, storing to date a total of 262 records. In this article we describe the development and evolution of the database, as well as its internal architecture. Additionally, a first global analysis of the data is provided with a special focus on length and slip-rate fault parameters. Finally, the database completeness and the internal consistency of the data are discussed. Even though QAFI v.2.0 is the most current resource for calculating fault-related seismic hazard in Iberia, the database is still incomplete and requires further review.RESUMEN. La Base de Datos de Fallas Activas de Iberia (QAFI) es una iniciativa promovida por el Instituto Geológico y Minero de España (IGME) para construir un repositorio público de información científica sobre fallas con actividad en los últimos 2,59 Ma (Cuaternario). Además, la QAFI persigue establecer una base sobre la que facilitar la transferencia de conocimiento geológico al ámbito tecnológico de la gestión del riesgo sísmico en Iberia, en particular en la identificación y caracterización de fuentes sismogénicas tipo falla. La QAFI se ha construido a partir de la información proporcionada de modo altruista por más de 40 investigadores en ciencias de la Tierra conteniendo actualmente un total de de 262 registros. En este artículo se describe la concepción y evolución de la base de datos, y su arquitectura interna. Además, se ofrece un primer análisis global de los datos que contiene, con especial interés en parámetros tan importantes como la longitud y tasa de deslizamiento de las fallas. Finalmente se discuten dos temas cruciales en cualquier base de datos: su completitud y la homogeneidad de los datos. Se concluye que QAFI v.2.0, pese a ser la fuente más actualizada de información disponible en Iberia sobre peligrosidad sísmica de fallas concretas, dista aun de ser completa, por lo que nuevas revisiones y versiones deberán seguir llevándose a cabo en el futuro

Compilation of parameterized seismogenic sources in Iberia for the SHARE European-scale seismic source model.

Abstract: SHARE (Seismic Hazard Harmonization in Europe) is an EC-funded project (FP7) that aims to evaluate European seismic hazards using an integrated, standardized approach. In the context of SHARE, we are compiling a fully-parameterized active fault database for Iberia and the nearby offshore region. The principal goal of this initiative is for fault sources in the Iberian region to be represented in SHARE and incorporated into the source model that will be used to produce seismic hazard maps at the European scale. The SHARE project relies heavily on input from many regional experts throughout the Euro-Mediterranean region. At the SHARE regional meeting for Iberia, the 2010 Working Group on Iberian Seismogenic Sources (WGISS) was established; these researchers are contributing to this large effort by providing their data to the Iberian regional integrators in a standardized format. The development of the SHARE Iberian active fault database is occurring in parallel with IBERFAULT, another ongoing effort to compile a database of active faults in the Iberian region. The SHARE Iberian active fault database synthesizes a wide range of geological and geophysical observations on active seismogenic sources, and incorporates existing compilations (e.g., Cabral, 1995; Silva et al., 2008), original data contributed directly from researchers, data compiled from the literature, parameters estimated using empirical and analytical relationships, and, where necessary, parameters derived using expert judgment. The Iberian seismogenic source model derived for SHARE will be the first regional-scale source model for Iberia that includes fault data and follows an internationally standardized approach (Basili et al., 2008; 2009). This model can be used in both seismic hazard and risk analyses and will be appropriate for use in Iberian- and European-scale assessments

The Quaternary Active Faults Database of Iberia (QAFI v.2.0)

The Quaternary Active Faults Database of Iberia (QAFI) is an initiative lead by the Institute of Geology and Mines of Spain (IGME) for building a public repository of scientific data regarding faults having documented activity during the last 2.59 Ma (Quaternary). QAFI also addresses a need to transfer geologic knowledge to practitioners of seismic hazard and risk in Iberia by identifying and characterizing seismogenic fault-sources. QAFI is populated by the information freely provided by more than 40 Earth science researchers, storing to date a total of 262 records. In this article we describe the development and evolution of the database, as well as its internal architecture. Aditionally, a first global analysis of the data is provided with a special focus on length and slip-rate fault parameters. Finally, the database completeness and the internal consistency of the data are discussed. Even though QAFI v.2.0 is the most current resource for calculating fault-related seismic hazard in Iberia, the database is still incomplete and requires further review