Neotectonic features of the Catalan Coastel Ranges, Northeastern Spain

The Catalan Coastal Ranges constitute the northwestem emerged sector of the Catalan-Valencian domain of the Valencia trough. Since late Oligocene this domain of the Valencia trough was subjected to extension wich gradually attenuated during later periods. The Miocene tectonic evolution of the Catalan Coastal Ranges is relativelly well known while the Pliocene to-Quaternary stages have not been studied in detail. The recorded seismicity of the area is moderate and constant but not sufficiently intense to cliaracterize and locate recent tectonics. However, geological analysis provides further information. A morphotectonic and deformational analysis of the Catalan Coastal Ranges is presented in this paper. Three main mountain fronts which show characteristic neotectonic features are examined: El Camp, El Baix Ebre and El Montseny mountain fronts. These fronts have faceted spurs, -with more than one generation in El Camp and El Montseny fronts-, moderate to low sinuosity (1.30-1.50), orthogonal drainage across the fault, "wine glass" drainage basins with moderate Se/L index -0.52 in El Baix Ebre front- and convexity in the topogr4phic profiles orthogonal to the front. Severa1 fault scarps are aligned parallel to the main faults in the southern half of the studied zone. Morphological anomalies are also apparent in the fluvial network, for example: asymmetrical drainage basins indicating tilting. Segmentation is noticeable in St. Jordi alluvial fan located near the Baix Ebre basin. Brittle deformation in Pliocene and Quaternary sediments is sparse, but is evident in St. Onofre outcrop (Baix Ebre) with normal faulting with vertical o1 and NNW-SSE ~3 in Pliocene sediments and NNW-SSE normal faults in Quaternary sediments. Liquefaction deformational features are described and may be related to paleoseismology. Vertical normal slip is inferred for the main neotectonic mountain fronts with more activity concentrated in the southern Catalan Coastal Ranges. Present-day tectonic activity is characterized as very small

An updated maximum likelihood approach to open cluster distance determination

An improved method for estimating distances to open clusters is presented and applied to Hipparcos data for the Pleiades and the Hyades. The method is applied in the context of the historic Pleiades distance problem, with a discussion of previous criticisms of Hipparcos parallaxes. This is followed by an outlook for Gaia, where the improved method could be especially useful. Based on maximum likelihood estimation, the method combines parallax, position, apparent magnitude, colour, proper motion, and radial velocity information to estimate the parameters describing an open cluster precisely and without bias. We find the distance to the Pleiades to be $120.3 \pm 1.5$ pc, in accordance with previously published work using the same dataset. We find that error correlations cannot be responsible for the still present discrepancy between Hipparcos and photometric methods. Additionally, the three-dimensional space velocity and physical structure of Pleiades is parametrised, where we find strong evidence of mass segregation. The distance to the Hyades is found to be $46.35\pm 0.35$ pc, also in accordance with previous results. Through the use of simulations, we confirm that the method is unbiased, so will be useful for accurate open cluster parameter estimation with Gaia at distances up to several thousand parsec.Comment: 14 pages, 8 figures, 6 tables, 3 appendices. Accepted in A&

Paleoseismic results from multiple trenching analysis along a silent fault: The El Camp fault (Tarragona, northeastern Iberian Peninsula)

We present the paleoseismological analysis of the El Camp fault scarp. Paleoseismology constitutes the key methodology for any real estimate of seismic hazard in low-slip-rate areas with no reported historical earthquakes. The recent tectonic activity of this fault is evidenced by a young mountain front and a fault scarp which cuts Quaternary alluvial fans. A regional geological analysis indicates that three generations of alluvial fans are cut by the fault. Absolute (TL and U/Th) and relative datings show that the oldest fan is 300ka old and the intermediate one is 125ka old. The study of 7 trenches and the absolute datings performed (TL, U/Th, radiocarbon as well as pollen analysis) revealed the following: 1) the El Camp fault consists of two segments (the northern end of the southern segment is located close to Porquerola creek); 2) only the southern segment has been active since 125 ka; 3) the fault is seismogenic because it is associated with liquefaction features and colluvial wedges; 4) the El Camp fault has produced at least three well constrained surface-rupturing earthquakes since 125ka (events Z, Y, and X). Based on the different tectonic features observed in the trenches, the recurrence period of large earthquakes during this period was estimated to be around 30ka and the elapsed time to be around 3000yr. Using the fault length and the vertical displacement per event, the largest estimated earthquake had a magnitude of MW 6.7 .

Expresión geomorfológica de la actividad reciente de la falla de Amer (NE de la Península Ibérica)

Triangular facets, related drainage basins, alluvial fans and subtle scarps reveal the recent activity of the normal Amer fault (NE Spain). The 1427 earthquakes which reached epicentral intensities ranging between VI1 and VI11 have been attributed to the Amer fault. However, the geomorphologic and geologic characteristics of this fault (30 km length) suggest that it might be capable of producing larger earthquakes than those occurred during de 15th century

Paleoseismic results from multiple trenching analysis along a silent fault: The El Camp fault (Tarragona, northeastern Iberian Peninsula)

We present the paleoseismological analysis of the El Camp fault scarp. Paleoseismology constitutes the key methodology for any real estimate of seismic hazard in low-slip-rate areas with no reported historical earthquakes. The recent tectonic activity of this fault is evidenced by a young mountain front and a fault scarp which cuts Quatern a ry alluvial fans. A regional geological analysis indicates that three generations of alluvial fans are cut by the fault. Absolute (TL and U/Th) and relative datings show that the oldest fan is 300 ka old and the intermediate one is 125 ka old. The study of 7 trenches and the absolute datings performed (TL, U/Th, radiocarbon as well as pollen analysis) revealed the following: 1) the El Camp fault consists of two segments (the nort h e rn end of the southern segment is located close to Po rquerola creek); 2) only the southern segment has been active since 125 ka; 3) the fault is seismogenic because it is associated with liquefaction features and colluvial wedges; 4) the El Camp fault has produced at least three well constrained surface-rupturing earthquakes since 125 ka (events Z, Y, and X). Based on the different tectonic features observed in the trenches, the recurrence period of large earthquakes during this period was estimated to be around 30 ka and the elapsed time to be around 3000 yr. Using the fault length and the ve rtical displacement per event, the largest estimated earthquake had a magnitude of Mw 6.7.Se presenta el análisis paleosismológico de la falla de El Camp. La paleosismología es una herramienta imprescindible para la caracterización sísmica de fallas activas, lentas y sin sismicidad histórica y, por lo tanto, para cálculos de peligrosidad sísmica. La falla de El Camp muestra evidencias de actividad tectónica: un frente montañoso joven y un escarpe de falla que afecta a abanicos aluviales cuaternarios. Un análisis geológico regional, previo al paleosismológico, muestra tres generaciones de abanicos aluviales afectados por la falla. El techo de éstos ha sido datado (U/Th y TL en caliches) en 300 y 125 ka para las dos generaciones más antiguas. Del estudio de 7 trincheras y de las dataciones por U/Th, TL, radiocarbono y polen se han obtenido los siguientes resultados: 1) La falla tiene dos segmentos con límite en el barranco de la Po rquerola. Solamente el segmento al sur de este punto ha sido activo posteriormente a 125 ka. 2) La falla de El Camp es sismogénica. 3) Se han caracterizado un mínimo de tres eventos posteriores a 125 ka (eventos Z, Y, y X). 4) El período intersísmico reciente se ha estimado en 30 ka. 5) El tiempo transcurrido desde el último terremoto es de 3000 años. 6) La magnitud del terremoto máximo es MW 6. 7

Tectónica activa de la Falla de Alhama de Murcia, Cordillera Bética, España

We present an overview of the knowledge of the structure and the seismic behavior of the Alhama de Murcia Fault (AMF). We utilize a fault traces map created from a LIDAR DEM combined with the geodynamic setting, the analysis of the morphology, the distribution of seismicity, the geological information from E 1:50000 geological maps and the available paleoseismic data to describe the recent activity of the AMF. We discuss the importance of uncertainties regarding the structure and kinematics of the AMF applied to the interpretation and spatial correlation of the paleoseismic data. In particular, we discuss the nature of the faults dipping to the SE (antithetic to the main faults of the AMF) in several segments that have been studied in the previous paleoseismic works. A special chapter is dedicated to the analysis of the tectonic source of the Lorca 2011 earthquake that took place in between two large segments of the fault.En este estudio se presenta una revisión del conocimiento que hasta la actualidad se tiene de la estructura y comportamiento sismogenético de la Falla de Alhama de Murcia (AMF). Se utiliza un nuevo mapa de la traza de la AMF realizado a partir de un modelo digital del terreno de alta resolución a partir de datos LIDAR, combinado con el análisis del marco geodinámico, la geomorforlogía, la distribución espaciotemporal de la sismicidad, la información geológica de trabajos previos y los datos paleosísmicos existentes, para describir la actividad reciente de la AMF. Se discute la importancia de las incertidumbres que se mantienen en relación con la estructura y la cinemática de la AMF para la correcta interpretación y correlación espacio-temporal de los datos paleosísmicos obtenidos hasta ahora. En particular, se discute la naturaleza de las fallas con buzamiento SE en superficie (antitéticas con las fallas principales de la AMF que bordean las sierras) en varios segmentos que han sido estudiados en análisis paleosismológicos previos. Se dedica un capítulo especial al análisis de la fuente geológica del terremoto de Lorca de 2011 que tuvo lugar en la zona de intersegmento que separa dos de los segmentos de mayor longitud de la AMF

Evidence for coseismic events of recurrent prehistoric deformation along the Alhama de Murcia fault, southeastern Spain

The Alhama de Murcia fault is a 85 km long oblique-slip fault, and is related to historical and instrumental seismic activity. A paleoseismic analysis of the Lorca-Totana sector of the fault containing MSK I=VIII historical earthquakes was made in order to identify and quantify its seismic potential. We present 1) the results of the neotectonic, structural and geomorphological analyses and, 2) the results of trenching. In the study area, the Alhama de Murcia fault forms a depressed corridor between two strands, the northwestern fault with morphological and structural features of a reverse component of slip, bounding the La Tercia range to the South, and the southeastern fault strand with evidence of sinistral oblique strike-slip movement. The offset along this latter fault trapped the sediments in transit from the La Tercia range towards the Guadalentín depression. The most recent of these sediments are arranged in three generations of alluvial fans and terraces. The first two trenches were dug in the most recent sediments across the southeastern fault strand. The results indicate a coseismic reverse fault deformation that involved the sedimentary sequence up to the intermediate alluvial fan and the Holocene terrace deposits. The sedimentary evolution observed in the trenches suggests an event of temporary damming of the Colmenar creek drainage to the South due to uplifting of the hanging wall during coseismic activation of the fault. Trench, structural and sedimentological features provide evidence of at least three coseismic events, which occurred after 125,000yr. The minimum vertical slip rate along the fault is 0.06mm/yr and the average recurrence period should not exceed 40,000yr in  accordance with the results obtained by fan topographic profiling. Further absolute dating is ongoing to constrain these estimates.