Paleoseismic analysis of the San Vicente segment of the El Salvador Fault Zone, El Salvador, Central America

The El Salvador earthquake of February 13th 2001 (Mw 6.6) was associated with the tectonic rupture of the El Salvador Fault Zone. Paleoseismic studies of the El Salvador Fault Zone undertaken after this earthquake provide a basis for examining the longer history of surface rupturing earthquakes on the fault. Trenching at five sites along the San Vicente segment, a 21km-long and up to 2km-wide central section of the El Salvador Fault Zone, shows that surface fault rupture has occurred at least seven times during the past 8ka. Single-event displacements identified at each trench vary from several decimetres to at least 3.7m. Fault trace mapping, geomorphic analysis, and paleoseismic studies indicate a maximum magnitude for the El Salvador Fault Zone is c. Mw 7.6, with a recurrence interval of around 800yr. Earthquakes of Mw 6.6 or smaller, such as the February 2001 event are unlikely to be identified in the paleoseismic trenches, so our observations represent the minimum number of moderate to large earthquakes that have occurred on this part of the El Salvador Fault Zone. We observe significant variability in single-event displacement in the trenches, which we interpret as possible cascade rupture of several segments of the El Salvador Fault Zone. Combining displacements of river courses and the timing of events revealed in the trenches, we calculate a slip rate of c. 4mm/yr for El Salvador Fault Zone, identifying the fault zone as a major tectonic feature of the region, and a major source of seismic hazard and risk in El Salvador

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 regionThis work forms part of the research activities carried out in the FASEGEO Project (CGL2009-09726) funded by the Spanish Ministry of Science and Innovatio

An approach for identifyation of areas with higher expected damage and definition of priority levels for prevention plans in Murcia Province (SE Spain)

The Murcia Region is one of the most active zones in Spain, where three earthquakes took place in 1999, 2002 and 2005. In spite of their low magnitudes (Mw 4.8), these earthquakes caused important damage, the last one reaching an EMS-98 intensity of VII. After that event, the RISMUR project started, aimed at providing a general picture of the seismic risk, which allows us to identify zones requiring a more detailed analysis of where prevention plans should be prioritized. A multidisciplinary study, starting with the seismic hazard assessment, which follows the Probabilistic Seismic Hazard Assessment methodology has been carried out at a regional scale. The expected ground motion (rock sites), for a return period of 475 years, has been characterized in terms of PGA and spectral ordinates and the corresponding maps have been drawn. In addition, a regional geotechnical study has been done and a classification of eight types of soils has been proposed, with the corresponding amplification factors. The combination of previous maps and factors, gives a new hazard map which already includes local effects. In parallel, a vulnerability assessment of the Murcian building stock is carried out, based fundamentally on the age of construction and following the EMS-98 criteria. Taking into account the expected ground motions and building vulnerabilities, the distribution of expected damage is estimated by the application of probability damage matrixes. A suite of maps representing seismic risk in terms of damage parameters for the entire region and from which we can identify the locations with higher expected damage have been obtained. We use the Coulomb stress transfer map of the region as additional criteria for defining priority areas where detailed studies should be performed. This gives information about the zones with stress load due to the previous seismicity and where new events could be triggered. The superposition of this map with the active faults of the region and the locations with higher expected damage allows us to establish a four-level priority ranking where future local-scale analyses should be made

An exceptionally long paleoseismic record of a slow-moving fault: the Alhama de Murcia fault (Eastern Betic Shear Zone, Spain)

Most catastrophic earthquakes occur along fast-moving faults, although some of them are triggered by slow-moving ones. Long paleoseismic histories are infrequent in the latter faults. Here, an exceptionally long paleoseismic record (more than 300 k.y.) of a slow-moving structure is presented for the southern tip of the Alhama de Murcia fault (Eastern Betic shear zone), which is characterized by morphological expression of current tectonic activity and by a lack of historical seismicity. At its tip, the fault divides into a splay with two main faults bounding the Góñar fault system. At this area, the condensed sedimentation and the distribution of the deformation in several structures provided us with more opportunities to obtain a complete paleoseismic record than at other segments of the fault. The tectonic deformation of the system was studied by an integrated structural, geomorphological, and paleoseismological approach. Stratigraphic and tectonic features at six paleoseismic trenches indicate that old alluvial units have been repeatedly folded and thrusted over younger ones along the different traces of the structure. The correlation of the event timing inferred for each of these trenches and the application of an improved protocol for the infrared stimulated luminescence (IRSL) dating of K-feldspar allowed us to constrain a paleoseismic record as old as 325 ka. We identifi ed a minimum of six possible paleoearthquakes of Mw = 6-7 and a maximum mean recurrence interval of 29 k.y. This provides compelling evidence for the underestimation of the seismic hazard in the region

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

ZFESNET GPS network to study the evolution of the seismic cycle of stress and strain associated to the El Salvador Fault zone

El Salvador se caracteriza por la presencia de fallas de desgarre sísmicamente activas subparalelas a la zona de subducción. Estas estructuras han sido las responsables de la mayoría de los terremotos destructivos que han tenido lugar a lo largo de la costa Pacífica en el arco volcánico centroamericano, desde Guatemala hasta Costa Rica. La Zona de Falla de El Salvador (ZFES) es una de las principales estructuras tectónicas de la región estudiada, y posiblemente la estructura donde se está acomodando la mayor parte del movimiento paralelo a la zona de subducción. En este trabajo se presenta la Red GPS ZFESNET, establecida en 2007 con el fin de cuantificar la deformación que se está produciendo actualmente asociada a la ZFES. La determinación de deformaciones y esfuerzos acumulados a partir de datos GPS permitirá complementar los datos geológicos existentes y contribuir a una correcta evaluación de la peligrosidad sísmica para esta zona, así como al mejor entendimiento de los datos de sismicidad histórica y paleosismicidad.El Salvador is characterized by the presence of active strike-slip faults subparallel to the trench. These structures have been responsible for most of the destructive earthquakes along the volcanic arc parallel to the pacific coast, from Guatemala to Costa Rica. The El Salvador fault zone is one of the main tectonic structures of the region, and it is possibly the most relevant structure accommodating trench-parallel motion. In this work we present the ZFESNET GPS network, established in 2007 with the aim to quantify the deformation and stress fields controlled by the current activity of the ESFZ. The determination of deformations and stresses from systematic GPS measurements will contribute to improve the seismic hazard assessments in the region and to a better understanding of the historical and paleoseismic activity in the areaDepto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEpu

Red GPS ZFESNET para el estudio de la evolución del ciclo sísmico de deformaciones y esfuerzos asociado a la zona de falla de El Salvador

El Salvador se caracteriza por la presencia de fallas de desgarre sísmicamente activas subparalelas a la zona de subducción. Estas estructuras han sido las responsables de la mayoría de los terremotos destructivos que han tenido lugar a lo largo de la costa Pacífica en el arco volcánico centroamericano, desde Guatemala hasta Costa Rica. La Zona de Falla de El Salvador (ZFES) es una de las principales estructuras tectónicas de la región estudiada, y posiblemente la estructura donde se está acomodando la mayor parte del movimiento paralelo a la zona de subducción. En este trabajo se presenta la Red GPS ZFESNET, establecida en 2007 con el fin de cuantificar la deformación que se está produciendo actualmente asociada a la ZFES. La determinación de deformaciones y esfuerzos acumulados a partir de datos GPS permitirá complementar los datos geológicos existentes y contribuir a una correcta evaluación de la peligrosidad sísmica para esta zona, así como al mejor entendimiento de los datos de sismicidad histórica y paleosismicidad

First month prednisone dose predicts prednisone burden during the following 11 months: An observational study from the RELES cohort

Aim: To study the influence of prednisone dose during the first month after systemic lupus erythematosus (SLE) diagnosis (prednisone-1) on glucocorticoid burden during the subsequent 11 months (prednisone-2–12). Methods: 223 patients from the Registro Español de Lupus Eritematoso Sistémico inception cohort were studied. The cumulative dose of prednisone-1 and prednisone-2–12 were calculated and recoded into a four-level categorical variable: no prednisone, low dose (up to 7.5 mg/day), medium dose (up to 30 mg/day) and high dose (over 30 mg/day). The association between the cumulative prednisone-1 and prednisone-2–12 doses was tested. We analysed whether the four-level prednisone-1 categorical variable was an independent predictor of an average dose >7.5 mg/day of prednisone-2–12. Adjusting variables included age, immunosuppressives, antimalarials, methyl-prednisolone pulses, lupus nephritis and baseline SLE Disease Activity Index (SLEDAI). Results: Within the first month, 113 patients (51%) did not receive any prednisone, 24 patients (11%) received average low doses, 46 patients (21%) received medium doses and 40 patients (18%) received high doses. There was a strong association between prednisone-1 and prednisone-2–12 dose categories (p7.5 mg/day, while patients receiving low-dose prednisone-1 were not (adjusted OR 1.4, 95% CI 0. 0.38 to 5.2). If the analysis was restricted to the 158 patients with a baseline SLEDAI of =6, the model did not change. Conclusion: The dose of prednisone during the first month after the diagnosis of SLE is an independent predictor of prednisone burden during the following 11 months

New paleoseismic data for the Alhama de Murcia Fault in the La Salud alluvial fan (Lorca-Totana segment) Betic Cordillera

La Falla de Alhama de Murcia (FAM) es una falla de desgarre sinestral y cierta componente inversa, que fue la responsable del terremoto más catastrófico producido en España en los últimos 50 años, el terremoto de Lorca de 2011 (Mw 5.2). En este trabajo se presenta el estudio de dos trincheras paleosísmicas excavadas en la superficie del abanico aluvial de La Salud que se encuentra cubriendo la traza de la FAM en el sector oriental del segmento Lorca-Totana. La excavación de las trincheras se apoya en la realización de una prospección geofísica mediante tomografía eléctrica y perfiles GPR con el objetivo de obtener nuevos datos de recurrencia sísmica en esta zona de la falla. Tanto las trincheras como los datos geofísicos son coherentes con la existencia de un plano de falla buzando 30º hacia el sur que deforma visiblemente los últimos depósitos del abanico. Las trincheras nos indican la ocurrencia de entre 3 y 6 eventos paleosísmicos de ruptura superficial en los últimos 31 ky.The Alhama de Murcia Fault (FAM) is a left-lateral strike-slip fault with reverse component. This fault is located in the southeast of Spain and produces the 2011 Lorca earthquake (Mw 5.2), that was the most catastrophic earthquake occurred in Spain in the last 50 years. In this paper we present the analysis of two paleoseismic trenches excavated in La Salud alluvial fan, with the aim to obtain new recurrence data for the eastern section of the Lorca- Totana segment of the fault. The structure that we observed in the trenches is recognizable in the electric tomography and GPR profiles undertaken in the study area. Both the paleoseismic trenches and the geophysics analysis are consistent with the existence of a fault plane dipping 30º to the south. This fault plane deforms the younger fluvial fan deposits. The paleoseismic study indicates the existence of between 3 and 6 surface rupture events in the last 31 ka for this strand of the fault.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEMinisterio de Economía y Competitividad (MINECO)pu