AC-DCFS: a toolchain implementation to Automatically Compute Coulomb Failure Stress changes after relevant earthquakes

We present an automated free software-based toolchain to obtain Coulomb Failure Stress change maps on fault planes of interest following the occurrence of a relevant earthquake. The system uses as input the focal mechanism data of the event occurred and an active fault database for the region. From the focal mechanism the orientations of the possible rupture planes, the location of the event and the size of the earthquake are obtained. From the size of the earthquake, the dimensions of the rupture plane are obtained by means of an algorithm based on empirical relations. Using the active fault database in the area, the stress-receiving planes are obtained and a verisimilitude index is assigned to the source plane from the two nodal planes of the focal mechanism. The obtained product is a series of layers in a format compatible with any type of GIS (or map completely edited in PDF format) showing the possible stress change maps on the different families of fault planes present in the epicentral zone. These type of products are presented generally in technical reports developed in the weeks following the occurrence of the event, or in scientific publications; however they have been proven useful for emergency management in the hours and days after a major event being these stress changes responsible of aftershocks, in addition to the mid-term earthquake forecasting. The automation of the calculation allows its incorporation within the products generated by the alert and surveillance agencies shortly after the earthquake occurred. It is now being implemented in the Spanish Geological Survey as one of the products that this agency would provides after the occurrence of relevant seismic series in Spain

Evaluación regional de inestabilidades de ladera por efecto sísmico: Mapas de desplazamiento de Newmark para la Cuenca de Lorca (SE España)

El sureste de España está caracterizado por una sismicidad de baja a moderada magnitud. Sin embargo, los terremotos de baja magnitud (Mw=4.0-4.5) pueden producir daños significativos en las edificaciones, así como inestabilidades de ladera (caída de rocas, principalmente). En este trabajo se presenta un mapa de desplazamientos de Newmark para la Cuenca de Lorca considerando diferentes escenarios sísmicos. Para su construcción se ha elaborado un mapa litológico basado en los mapas geológicos del IGME, asignando a cada unidad valores de peso específico, cohesión y ángulo de fricción obtenidos de bibliografía y de ensayos geotécnicos. Estos mapas se combinan con el mapa de pendientes generado a partir de un modelo digital de elevaciones (MDE) para obtener un mapa de factores de seguridad estáticos. Combinando éste con el de pendientes se obtiene el mapa de aceleraciones críticas (ac) que representa la susceptibilidad sísmica al deslizamiento. Se han considerado varios escenarios sísmicos para los que se ha aplicado factores de amplificación del terreno y topográfico para obtener los mapas de aceleración sísmica máxima (PGA). Los desplazamientos de Newmark (DN) se obtienen empleando una ecuación empírica en función del ratio K (ac/PGA). Los mapas obtenidos permiten identificar las áreas de potencial riesgo en la Cuenca de Lorca. En general, las inestabilidades esperables serán de tipo desprendimiento, particularmente caídas de rocas

Estimation of vertical slip rate in an active fault-propagation fold from the analysis of a progressive unconformity at the NE segment of the Carrascoy Fault (SE Iberia)

Many studies have dealt with the calculation of fault-propagation fold growth rates considering a variety of kinematics models, from limb rotation to hinge migration models. In most cases, the different geometrical and numeric growth models are based on horizontal pre-growth strata architecture and a constant known slip rate. Here, we present the estimation of the vertical slip rate of the NE Segment of the Carrascoy Fault (SE Iberian Peninsula) from the geometrical modeling of a progressive unconformity developed on alluvial fan sediments with a high depositional slope. The NE Segment of the Carrascoy Fault is a left-lateral strike slip fault with reverse component belonging to the Eastern Betic Shear Zone, a major structure that accommodates most of the convergence between Iberian and Nubian tectonics plates in Southern Spain. The proximity of this major fault to the city of Murcia encourages the importance of carrying out paleosismological studies in order to determinate the Quaternary slip rate of the fault, a key geological parameter for seismic hazard calculations. This segment is formed by a narrow fault zone that articulates abruptly the northern edge of the Carrascoy Range with the Guadalentin Depression through high slope, short alluvial fans Upper-Middle Pleistocene in age. An outcrop in a quarry at the foot of this front reveals a progressive unconformity developed on these alluvial fan deposits, showing the important reverse component of the fault. The architecture of this unconformity is marked by well-developed calcretes on the top some of the alluvial deposits. We have determined the age of several of these calcretes by the Uranium-series disequilibrium dating method. The results obtained are consistent with recent published studies on the SW segment of the Carrascoy Fault that together with offset canals observed at a few locations suggest a net slip rate close to 1 m/ka

Estudio preliminar de la estabilidad en condiciones dinámicas del deslizamiento de Bàlitx (Sierra de Tramuntana, Mallorca)

En este trabajo se realiza un estudio preliminar de estabilidad retrospectivo en condiciones dinámicas del deslizamiento de Bàlitx (Mallorca). Este gran movimiento de ladera se localiza en la franja costera del sector central de la Sierra de Tramuntana, en la parte noroccidental de la isla de Mallorca. El área se caracteriza por el predominio de materiales rocosos carbonatados (calizas y dolomías) del Jurásico inferior (Lías) que configuran espectaculares acantilados rocosos de varios centenares de metros de altura. En el caso del deslizamiento de Bàlitx, estos materiales carbonatados se disponen sobre los materiales blandos del Triásico (facies Keuper), constituidos principalmente por margas y arcillas con yesos. Teniendo en cuenta que en la isla de Mallorca existen registros de sismicidad histórica y que, además, presenta una peligrosidad sísmica moderada, el estudio en condiciones dinámicas del deslizamiento de Bàlitx ha permitido confirmar su posible origen sísmico. Se ha estimado que el deslizamiento pudo ser provocado por un terremoto de magnitud moderada a alta (Mw=4.7-6.5) localizado en las inmediaciones del deslizamiento (≤ 20 km). [ABSTRACT]In this work we perform a slope stability back-analysis of the Bàlitx landslide in dynamic conditions. This slope instability is located on the coast of the central sector of the Tramuntana Range, in Majorca Island. This area is characterized by the predominance of Jurassic limestones, on which spectacular cliffs of several hundred metres have been developed. In the Bàlitx landslide, these carbonated materials lie on top of Triassic soft materials (Keuper facies), composed mainly of marls and clays with gypsum. In this work we focus on analyzing the possibility that the Bàlitx landslide was triggered by an earthquake. Majorca Island, although it is considered as a region of low-to-moderate seismic hazard, shows historical damaging earthquakes and Quaternary active faults. We have concluded preliminary that the Bàlitx landslide could have been triggered by a moderate-to-large earthquake (Mw=4.7-6.5) located relatively close to the landslide (≤ 20 km)

Seismogenic zoning based on the geothermal gradient, strenght and depth of the fragile-ductile transition in the upper crust. Methodological approach for seismic hazard calculations in southeast Spain

In this work we present a methodological approach to define seismogenic zones for seismic hazard analysis based on the relationships which can be drawn from the geothermal gradient, total strength of the upper crust and the depth of the fragile-ductile transition, and their relation with the mean focal depth and a parameter hereby defined: Seismic Density Index (number of events per km3 x 1000). A revision of the deep geophysical data available in SE Spain has led to the definition of 6 distinctive crustal blocks. Two main types of crustal blocks are identified: hot-and-weak and cold-and-strong. Hot-and-weak blocks show consistently higher geothermal gradients, lower strengths and shallower fragile-ductile depths than coldand- strong blocks. Furthermore hot-and-weak blocks show higher seismic density indexes and shallower mean focal depths. However, two blocks biased from this relationship and so are called anomalous. According to these results four seismogenic zones can be defined in SE Spain. The a and b parameters of the Gutenberg-Richter law of each zone are consistent with the thermal and strength properties of the blocks. Zones based on the hot-and-weak blocks show higher a and b values than the cold-and-strong ones, while the anomalous blocks show values in between these extreme

SeriesBuster: extrayendo series de catálogos sísmicos

To carry out any kind of research involving earthquakes, and very specially: their interactions, it is necessary to classify and order them to tackle the issue appropriately. SeriesBuster is a program created to filter and classify events from catalogues that often comprise thousands of shocks. Series-Buster filters the records from an Excel .xls file by their depth, magnitude, distance and time difference between events and any special feature marked by a flag. This program extracts those records that fit the user requirements and saves them into an output ascii file. The shocks are numbered in series and ordered chronologically. There are multiple applications for this program: analysing statistically catalogues, obtaining those events that could have been triggered or involved in a seismic series, studying the fault rupture mechanism, etc. This program runs under Windows environment and was developed in Matlab; its code and stand-alone executables files are available from the authors upon request

Comparación entre las técnicas AEOS, Re-Mi y PS-logging aplicadas en un terreno de estructura profunda conocida

En este estudio se contrastan los resultados que ofrecen dos técnicas de uso habitual en el Laboratorio de Geotecnia del CEDEX, el AEOS y el PS-logging, con los de una técnica relativamente novedosa, el Re-Mi (o sísmica pasiva). Para ello se emplean los resultados obtenidos por las tres técnicas en un emplazamiento común de estructura profunda conocida: un tramo de terraplén ferroviario recién construido. La técnica más precisa en la identificación de las diferentes partes de la estructura de tierras (terraplén, cimiento y contacto con el terreno natural) es el PS-logging, seguido por el AEOS y Re-Mi. Los valores de Vs promedio proporcionados por cada técnica presentan importantes diferencias, obteniéndose los más altos con el PS-logging, seguido por AEOS y Re-Mi. La desviación de los valores Vs promedio obtenidos por una técnica en particular, en comparación con las otras, es similar. Respecto a la técnica Re-Mi, cabe destacar que, si bien no se ha mostrado muy precisa en este estudio, presenta un alto grado de operatividad en cuanto a implantación, ejecución y procesado de datos

Comparison among SASW, ReMi and PS-logging techniques: Application to a railway embankment

Results obtained by SASW and PS-logging (in-hole) seismic techniques are compared with the relatively new ReMi (Refraction microtremor) method at a common site with a well-known soil profile: a recently constructed high-speed railway embankment. PS-logging is the most accurate technique in identifying the soil profile of the embankment followed by Re-Mi and SASW. Mean shear wave velocity estimations are also higher for PS-logging, followed by SASW and ReMi, while mean deviation is similar in each technique. The ReMi technique has provided very accurate results in the study of the embankment profile, which in addition to its high operability and its fast data processing, makes it a very convenient technique for extensive geotechnical survey

Slip Rate Variation During the Last ∼210 ka on a Slow Fault in a Transpressive Regime: The Carrascoy Fault (Eastern Betic Shear Zone, SE Spain)

Fault slip rate variability over time is a crucial aspect for understanding how single faults interact among each other in fault systems. Several studies worldwide evidence the occurrence of high activity periods with clustering of events and synchronization among faults, followed by long periods of low activity (super-cycles). The increasing gathering of evidence of these phenomena is making fault hazard models quickly evolving and challenging seismic hazard assessment. However, in moderately active fault systems, a determination of fault slip rates can present large uncertainties, that have to be carefully considered when slip rate histories are determined. In this work, we estimate the variation of slip rate in the last ∼210 ky of the NE segment of the left-lateral reverse Carrascoy Fault, one of the main faults forming the Eastern Betic Shear Zone in SE Spain. We study two selected field sites where we have been able to measure offsets and date the sediments along with uncertainties. The first site shows a progressive discordance drawn by different calcretes developed on alluvial deposits. The vertical throw is calculated by modeling the growth of the discordance. The vertical slip rates are estimated dating the deformed calcretes by Uranium Series and by comparing them with a complete regional calcrete dates database compiled from the literature. On the second site, we analyze the geomorphology of different Upper Pleistocene alluvial fans, where three incised channels are offset by the fault, providing the net slip for the last ∼124 ky. We discuss the influence of different factors on the estimate of net slip rates using data from different sources. This analysis highlights the importance of determining an accurate fault geometry and how local data can provide misleading deformation rates. Our results suggest the existence of long periods of low activity disturbed by short high activity periods. Such a pattern of activity along time is defined for the first time in the Eastern Betic Shear Zone, with interesting implications in the seismogenic behavior of the rest of the slow faults within the region

Points and areas prone to earthquake-induced landslides in the CARM. Base information for Civil Protection

Se presenta un trabajo de aplicación para la definición de posibles escenarios de catástrofe sísmica, donde deben de incorporarse los movimientos de ladera, como información de base para la última revisión del Plan Especial de Protección Civil ante el Riesgo Sísmico en la Región de Murcia (SISMIMUR). Para ello se ha confeccionado un inventario adecuado y un mapa a escala 1:200.000 que contiene los puntos y zonas más susceptibles a este tipo de fenómenos inducidos por los terremotos en la CARM que pueden afectar a núcleos urbanos, infraestructuras lineales (carreteras y ferrocarriles), balsas mineras, cursos de agua y cuerpos de agua (embalses y lagos). En el análisis solo se han seleccionado los puntos definidos como desprendimientos s.l., tipología predominante en la zona de estudio y de mayores efectos de cara al escenario de la catástrofe sísmica posible. Aunque en la mayoría de las infraestructuras evaluadas están alejadas de movimientos de ladera inventariados, hay núcleos de población importantes como Lorca, Águilas o Caravaca de la Cruz, entre otras, así como algunos tramos del creciente entramado urbano del litoral murciano con zonas de susceptibilidad alta. El tramo más susceptible sería el situado en la carretera RM-520, entre Archena y Abarán.In this work, we present a methodology to define potential seismic scenarios including seismic-induced landslides as background information for the latest revision of the “Plan Especial de Protección Civil ante el Riesgo Sísmico en la Región de Murcia (SISMIMUR)”. We first made an adequate inventory and a map at 1:200,000 scale containing the points and areas more susceptible to this type of seismic-induced effects in the CARM which may affect urban areas, lifelines(roads and railways), tailing dams, waterways and bodies of water (reservoirs and lakes). For this analysis, only points defined as rockfalls s.l. have been selected, since they are the predominant type of landslide in the area and it is associated to the greatest effects regarding a potential seismic scenario. Although most of the infrastructures evaluated are far from the inventoried landslides, some areas with high susceptibility have been identified near major population centers, such as Lorca, Águilas, Caravaca de la Cruz, etc., and near of some growing urban fabric areas located along the Murcia province coast. According to this study, the most vulnerable section would be located in the RM-520 road between Archena and Abarán