La serie sísmica de Tivissa, 1845 (cadenas costeras catalanas): Los deslizamientos del barranco del Manou

La serie sísmica de Tivissa tuvo lugar durante la lluviosa década de 1840-1850, 21 días después de los aguaceros que ocasionaron graves inundaciones. La serie empezó el 30 de septiembre y finalizó el 14 de octubre. Los terremotos de mayor intensidad ocurrieron el 3 (IEMS-98=VI) y el 7 de octubre (IEMS-98=VI-VII). De acuerdo con la distribución de la información macrosísmica se propone un área epicentral para ambos terremotos entre Tivissa y Vandellòs. El sismo del 7 de octubre indujodeslizamientos de masa al Sur de Tivissa. La estratigrafía, la disposición estructural y la orografía facilitaron estos deslizamientos: tuvieron lugar en una secuencia de capas calcáreas, decimétricas, con interestratos centimétricos de margas que buzan en el mismo sentido que la pendiente de la vertiente del valle, pero menos que ésta, y que está afectada por diaclasas perpendiculares a la estratificación. Ello implica la existencia de masas rocosas aisladas por la estratificación y las diaclasas, susceptibles de deslizarse hacia el valle. El agua de los aguaceros que precedieron a los sismos infiltrada por las diaclasas podría haber facilitado el despegue a nivel de los interestratos margosos. Teniendo en cuenta los datos geológicos y sismológicos se discuten las posibles fuentes de estos terremotos.

Prospects for Paleoseismology in Spain

Paleoseismology is the study of prehistoric earthquakes, especially their location, timing and size. Paleoseismology and Neotectonics should not be confused. Whereas Neotectonics deals with general crustal deformation in recent times (late Cenozoic), Paleoseismology is concerned with sudden deformation of landforms and sediments during earthquakes. Paleoseismologists are only able to study earthquakes that produce recognizable surface deformation, i.e. earthquakes of M>6...

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 125,000 yr. The minimum vertical slip rate along the fault is 0.06 mm/yr and the average recurrence period should not exceed 40,000 yr in accordance with the results obtained by fan topographic profiling. Further absolute dating is ongoing to constrain these estimates.