Regional assessment of seismically induced slope instabilities in the Lorca Basin (Murcia): Implementation of Newmark’s method in a GIS

La Cuenca de Lorca (Murcia, SE España) constituye un territorio de gran interés para estudios de sismicidad y fenómenos inducidos ya que en ella se registra una elevada actividad sísmica, se localizan algunas de las fallas activas con mayor potencial sísmico de España y existen casos reconocidos de desprendimientos asociados a terremotos (e.g., Mula 1999, Bullas 2002, La Paca 2005). En esta área, se ha desarrollado una aplicación a escala regional del método del “bloque rígido deslizante” de Newmark en un sistema de información geográfica (SIG). Además, en este trabajo hemos propuesto una modificación del método de Newmark para tener en cuenta los efectos de amplificación sísmica relacionados con el suelo y con la topografía. Posteriormente, se han generado los mapas de desplazamiento de Newmark considerando tanto escenarios sísmicos deterministas como probabilistas para la Cuenca de Lorca. El cálculo del factor de seguridad estático para cada píxel del área de estudio ha permitido obtener un mapa de aceleración crítica (ac), el cual representa la susceptibilidad de las laderas a inestabilidades inducidas sísmicamente. Los mapas de desplazamiento de Newmark obtenidos permiten identificar las áreas con mayor peligrosidad así como zonas de interés para posteriores estudios de detalle. Los resultados predicen la mayoría de las inestabilidades observadas en trabajos previos (principalmente, desprendimientos) y los desprendimientos asociados a terremotos concretos con valores de desplazamiento de Newmark menores de 2 cm. Inestabilidades de mayor entidad y deslizamientos ocurrirían con desplazamientos de Newmark mayores de 2 cm para lo que se requeriría un terremoto de gran magnitud (Mw=6.7-6.8).The Lorca Basin (Murcia, SE Spain) exhibits a high seismic activity because some of the most active faults in Spain have been identified in the surroundings of this basin and there are well known cases of rock-falls associated to specific earthquakes (e.g., Mula 1999, Bullas 2002, La Paca 2005). In this area, we have used a geographic information system (GIS) to develop an implementation for the Newmark’s sliding rigid block method at a regional scale. In addition, we have particularly proposed a new small variation of Newmark’s method to consider soil and topographic amplification effects. Subsequently, we produce “Newmark displacement” maps for both deterministic and probabilistic seismic scenarios in the Lorca Basin. The estimation of static safety factor for each pixel of study area has allowed obtaining the critical acceleration (ac) map that represents seismically induced slope instability susceptibility. The obtained Newmark displacement maps allowed us to identify areas with the highest potential seismic hazard as well as interesting areas for future particular studies. The results predict the majority of identified instabilities in previous studies (mainly, rock-falls) and rock-falls associated with specific earthquakes with values of Newmark displacement lower than 2 cm. Larger instabilities and landslides occur with Newmark displacement higher than 2 cm assuming that a great earthquake (Mw=6.7-6.8) take place.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEAndalucia. Juntapu

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