A geodetic coseismic fault-slip model for the May, 11th 2011 Lorca earthquake using radar interferometry and GPS

[ES] La falla de Alhama de Murcia (FAM) está compuesta por diferentes segmentos con movimiento de desgarre siniestral con componente inversa. La FAM es una de las fallas de mayor longitud en las Béticas (sudeste de España). Así, en las últimas décadas su potencial sismogenético se ha evaluado usando principalmente datos de paleo-sismicidad. El 11 de mayo de 2011 un terremoto de magnitud momento moderada (Mw 5.1) sacudió Lorca, causando nueve muertes y cuantiosos daños materiales. La localización inicial de la secuencia de replicas no sugería ninguna tendencia en particular. Por otro lado, inspecciones geológicas realizadas in situ no identificaron ninguna fractura superficial que se pudiera asociar a deformación cosísmica. Para poder mejorar la evaluación del peligro sísmico en la zona, es necesario localizar y, si es posible, caracterizar la distribución del deslizamiento en la falla que generó este terremoto. En este trabajo presentamos deformaciones corticales pequeñas, pero significativas, medidas en la zona epicentral del terremoto de Lorca mediante el uso de técnicas geodésicas (interferometría radar de satélite y GPS). Los datos radar se procesaron obteniendo un conjunto de interferogramas diferenciales (corregidos por un hundimiento continuado debido a extracción de agua subterránea). Se han obtenido estimaciones GPS de coordenadas tanto diarias como a altas frecuencias (1-Hz). Hemos realizado una inversión conjunta de los desplazamientos cosísmicos detectados con ambas técnicas para determinar los parámetros del plano de falla, considerando un modelo de dislocación rectangular en un semiespacio elástico. El plano de falla ajustado sigue la geometría estimada geológicamente para la FAM (orientación NE-SW y buzamiento de ~70º NW). Posteriormente, a partir del modelo con deslizamiento homogéneo obtenido, el plano de falla se extiende y divide en segmentos, permitiendo un análisis más detallado del patrón de distribución de deslizamiento sobre el plano de falla. La distribución de deslizamiento obtenida indica que este ocurrió en un segmento principal de unos 4- 5 km de longitud con movimiento inverso y siniestral (con una magnitud máxima de deslizamiento de ~20 cm). El modelado también indica que una parte del deslizamiento ocurrió cerca de la superficie bajo la zona central y suroeste de la ciudad de Lorca. El carácter somero del deslizamiento a lo largo del plano de falla, así como el efecto amplificador producido por la finalización de la ruptura bajo el sudoeste de la ciudad probablemente fue el causante de la relativamente alta intensidad de la aceleración registrada (~0.4g). Esta ha sido la primera vez que se ha detectado claramente deformación cosísmica producida por un terremoto en la Península Ibérica mediante el uso de técnicas geodésicas modernas (InSAR y GPS), y permitiendo invertir de forma rigurosa las características del terremoto.[EN] The Alhama de Murcia Fault (AMF) is a compound multi-segmented oblique left-lateral fault system. The AMF is one the longest faults in the Eastern Betics Shear zone (Southeastern Spain). In the last decades its seismogenic potential has been carefully evaluated based on paleoseismological data. On May 11th, 2011 a moderate (Mw 5.1) earthquake shook the region, causing nine casualties and severe damage in Lorca city (Murcia region). The early reported location of the aftershock sequence did not draw any particular trend; furthermore in-situ geology surveys did not identify any surface coseismic slip-related ground deformation. In order to provide better seismic hazard assessments, we need to locate and, if possible, characterize the fault-slip distribution that generated this earthquake. In this work, we detected small but significant ground deformation close to the epicentral area of the Lorca earthquake by using geodetic (satellite radar interferometry and GPS) data. Geodetic data was processed by using a stack of differential radar interferograms (corrected for a known long-term subsidence contribution), daily GPS estimated coordinates and high-rate 1-Hz GPS data. We jointly inverted the detected static coseismic displacements for the fault plane geometry parameters by using a rectangular dislocation model embedded in a homogeneous elastic half-space. The best-fitting fault plane closely follows the geologically derived AMF geometry (NE-SW strike trend and dipping ~70º to NW). Later, the obtained model geometry was extended and divided into patches to allow for a detailed analysis of the fault slip distribution pattern. Slip distribution indicates that slip occurred in a main patch –4-5 km long– with reverse and leftlateral motion (with peak fault slip magnitude of ~20 cm). However, the modelling results also indicate that fault slip occurred close to the surface along the centre and southwest of the city of Lorca. The shallower character of the slip and the effect of a finite dynamic rupture fault arrest probably caused the relatively intense ground acceleration recorded in the city of Lorca (~0.4g) and increased the building damage. This study also represents the first modern geodetically observed ground deformation signature due to seismic activity in the Iberian Peninsula.Peer reviewe

The 2011 Lorca earthquake slip distribution controlled by groundwater crustal unloading

Earthquake initiation, propagation and arrest are influenced by fault frictional properties1, 2 and preseismic stress. Studies of triggered and induced seismicity can provide unique insights into this influence. However, measurements of near-field, surface ground deformation and pre-earthquake stress conditions necessary for such studies are rare. Here, we use geodetic data to determine surface deformation associated with the Mw 5.1 earthquake that occurred in Lorca, southeast Spain, on 11 May 2011. We use an elastic dislocation model to show that earthquake nucleation and the area of main fault slip occurred at very shallow depths of 2–4 km, on a rupture plane along the Alhama de Murcia Fault. Slip extended towards the surface, across fault segments with frictional properties that changed from unstable to stable. The area of fault slip correlates well with the pattern of positive Coulomb stress change that we calculate to result from the extraction of groundwater in a nearby basin aquifer. We therefore suggest that the distribution of shallow slip during the Lorca earthquake could be controlled by crustal unloading stresses at the upper frictional transition of the seismogenic layer, induced by groundwater extraction. Our results imply that anthropogenic activities could influence how and when earthquakes occur.Peer reviewe

Are the source models of the M 7.1 1908 Messina Straits earthquake reliable? Insights from a novel inversion and a sensitivity analysis of levelling data

For decades, many authors have attempted to define the location, geometry and kinematics of the causative fault for the 1908 December 28, M 7.1 earthquake that struck the Messina Straits between Sicily and Calabria (southern Italy). The coseismic displacement caused a predominant downwarping of the Straits and small land uplift away from it, which were documented by levelling surveys performed 1 yr before and immediately after the earthquake. Most of the source models based on inversion of levelling data suggested that the earthquake was caused by a low angle, east-dipping blind normal fault, whose upper projection intersects the Earth surface on the Sicilian (west) side of the Messina Straits.An alternative interpretation holds that the causative fault is one of the high-angle, west-dipping faults located in southern Calabria, on the eastern side of the Straits, and may in large part coincide with the mapped Armo Fault. Here, we critically review the levelling data with the aim of defining both their usefulness and limits in modelling the seismogenic fault. We demonstrate that the levelling data alone are not capable of discriminating between the two oppositely dipping fault models, and thus their role as a keystone for modellers is untenable. However, new morphotectonic and geodetic data indicate that the Armo Fault has very recent activity and is accumulating strain. The surface observations, together with appraisal ofmacroseismic intensity distribution, available seismic tomography and marine geophysical evidence, lends credit to the hypothesis that the Armo and possibly the S. Eufemia faults are part of a major crustal structure that slipped during the 1908 earthquake.Published1025-1041JCR Journalrestricte

Exogenous Interleukin-2 Administration Corrects the Cell Cycle Perturbation of Lymphocytes from Human Immunodeficiency Virus-Infected Individuals

Human immunodeficiency virus (HIV)-induced immunodeficiency is characterized by progressive loss of CD4(+) T cells associated with functional abnormalities of the surviving lymphocytes. Increased susceptibility to apoptosis and loss of proper cell cycle control can be observed in lymphocytes from HIV-infected individuals and may contribute to the lymphocyte dysfunction of AIDS patients. To better understand the relation between T-cell activation, apoptosis, and cell cycle perturbation, we studied the effect of exogenous interleukin-2 (IL-2) administration on the intracellular turnover of phase-dependent proteins. Circulating T cells from HIV-infected patients display a marked discrepancy between a metabolic profile typical of G(0) and a pattern of expression of phase-dependent proteins that indicates a more-advanced position within the cell cycle. This discrepancy is enhanced by in vitro activation with ConA and ultimately results in a marked increase of apoptotic events. Conversely, treatment of lymphocytes with IL-2 alone restores the phase-specific pattern of expression of cell cycle-dependent proteins and is associated with low levels of apoptosis. Interestingly, exogenous IL-2 administration normalizes the overall intracellular protein turnover, as measured by protein synthesis, half-life of newly synthesised proteins, and total protein ubiquitination, thus providing a possible explanation for the effect of IL-2 on the intracellular kinetics of cell cycle-dependent proteins. The beneficial effect of IL-2 administration is consistent with the possibility of defective IL-2 function in vivo, which is confirmed by the observation that lymphocytes from HIV-infected patients show abnormal endogenous IL-2 paracrine/autocrine function upon in vitro mitogen stimulation. Overall these results confirm that perturbation of cell cycle control contributes to HIV-related lymphocyte dysfunction and, by showing that IL-2 administration can revert this perturbation, suggest a new mechanism of action of IL-2 therapy in HIV-infected patients