ResumenEste estudio está enfocado a la caracterización de efectos sísmicos locales en la ciudad de Lorca y corresponde a uno de los aspectos de interés de una campaña de intervención post-sísmica organizada por Institut Geològic de Catalunya (IGC), la Universitat Politécnica de Catalunya (UPC), la Asociación Española de Ingeniería Sísmica (AEIS) conjuntamente con las asociaciones de ingeniería sísmica francesa (AFPS) y portuguesa (SPES) con el objetivo de calibrar, verificar y validar las metodologías de evaluación del riesgo sísmico que estos organismos utilizan. Se presenta el trabajo realizado y los resultados obtenidos para caracterizar la capa de suelos blandos aplicando dos técnicas basadas en medidas de ruido sísmico ambiental: la técnica del cociente espectral H/V y la técnica de "array". El registro de réplicas en distintos emplazamientos ha permitido obtener la respuesta sísmica de estos sitios. A partir de la información obtenida en los trabajos geofísicos de campo se han definido columnas de suelo representativas, se ha podido clasificar el tipo de suelo según el Eurocódigo 8, se ha modelizado su respuesta sísmica y se ha estimado el incremento de intensidad macrosísmica debido a la presencia de suelos blandos. Palabras clave: Efectos locales, ruido sísmico, Vs30, EC8, Simulación numérica, Sismo de Lorca. Site effects characterization in Lorca city AbstractThis study is focused on the characterization of seismic local effects in Lorca city. This aspect fits to one of the interesting points of a field survey for a post-seismic inspection organized by Institut Geològic of Catalonia (IGC), the Universitat Politècnica of Catalonia (UPC), the Spanish Association of Seismic Engineering (AEIS) together with the Earthquake Engineering Associations of France (AFPS) and Portugal (SPES) with the aim to calibrate, check and validate methodologies for seismic risk assessment that these organisms use. We present the work done and the obtained results in order to characterize the soil layers applying two passive seismic techniques: the H/V spectral ratio and the array method. The record of aftershocks in different emplacements has allowed us to obtain the soil seismic response of these sites. The information obtained from the geophysical field survey allowed the definition of representative soil columns and the soil classification according the Eurocode 8. Subsequently, the soil seismic response has been modelled and the increase of macroseismic intensity due to the presence of soft soils has been assessed.
Seismic crisis occurred in Lorca (Murcia) on 11 th May 2011 originated an important number of accelerograms recorded in the IGN stations. The analysis of uniformly computed parameters has produced interesting results for Earthquake Engineering, in particular those recorded in Lorca. Strong ground motion has been specially observed in the horizontal component perpendicular to the Alhama de Murcia fault, at the origin of the earthquake. Values of PGA= 0,37g and CAV= 0.27g•s seems to be compensated by a short duration of the motion producing a macroseismic Intensity not greater than VII in Lorca. The contribution of near field component of ground motion due to the rupture propagation to and under the Lorca town was shown on acceleration, velocity and displacement time series and also on elastic response spectra.
The main aim of this study is to demonstrate the feasibility of an earthquake early warning system (EEWS) to warn of potentially destructive earthquakes in the Cape San Vicente (SV) and Gulf of Cádiz (GC) areas in the southwest Iberian Peninsula, based on real-time broadband stations existing in the region. Historic earthquakes in this region include the 1755 Lisbon (M w 8.5) and 1969 SV (M w 7.8) events. This study illustrates the design, configuration, and first results of an EEWS prototype based on the U.S. Geological Survey Earthworm tools and developed at the Institut Cartogràfic i Geològic de Catalunya (ICGC). System main functionalities are real-time data acquisition, processing (P-wave picking, event detection, earthquake hypocentral location, and magnitude estimation from previously calculated peak displacement [P d ] and predominant period τ c of the P-wave signal), data archiving, and earthquake early warning dissemination. The prototype was put into operation after a setup period, during which several simulations were carried out to establish the optimal settings. After the first year of operation, one felt earthquake occurred in the area of study. Location and magnitude results are fairly good, compared with the Instituto Geográfico Nacional (IGN) catalog. Lead times obtained are on the order of tens of seconds for the majority of targets, which are long enough to mitigate damage for a large area of the southern coasts of Portugal and Spain due to the GC and SV earthquakes. Preliminary results for this prototype demonstrate the possibility of a regional, reliable, and effective EEWS in southwest Iberia.
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