Observatori de lEbre

Horta-Guinardó, Spain

Observatori de lEbre

Horta-Guinardó, Spain
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Cesca S.,German Research Center for Geosciences | Cesca S.,University of Potsdam | Grigoli F.,University of Potsdam | Heimann S.,German Research Center for Geosciences | And 7 more authors.
Geophysical Journal International | Year: 2014

A spatially localized seismic sequence originated few tens of kilometres offshore the Mediterranean coast of Spain, close to the Ebro river delta, starting on 2013 September 5, and lasting at least until 2013 October. The sequence culminated in a maximal moment magnitude MW 4.3 earthquake, on 2013 October 1. The most relevant seismogenic feature in the area is the Fosa de Amposta fault system, which includes different strands mapped at different distances to the coast, with a general NE-SW orientation, roughly parallel to the coastline. However, no significant known historical seismicity has involved this fault system in the past. The epicentral region is also located near the offshore platform of the Castor project, where gas is conducted through a pipeline from mainland and where it was recently injected in a depleted oil reservoir, at about 2 km depth. We analyse the temporal evolution of the seismic sequence and use full waveform techniques to derive absolute and relative locations, estimate depths and focal mechanisms for the largest events in the sequence (with magnitude mbLg larger than 3), and compare them to a previous event (2012 April 8, mbLg 3.3) taking place in the same region prior to the gas injection. Moment tensor inversion results show that the overall seismicity in this sequence is characterized by oblique mechanisms with a normal fault component, with a 30° low-dip angle plane oriented NNE-SSW and a subvertical plane oriented NW-SE. The combined analysis of hypocentral location and focal mechanisms could indicate that the seismic sequence corresponds to rupture processes along shallow low-dip surfaces, which could have been triggered by the gas injection in the reservoir, and excludes the activation of the Amposta fault, as its known orientation is inconsistent with focal mechanism results. An alternative scenario includes the iterated triggering of a system of steep faults oriented NW-SE, which were identified by prior marine seismics investigations. © The Authors 2014. Published by Oxford University Press on behalf of The Royal Astronomical Society.

Marcos R.,Barcelona Supercomputing Center | Marcos R.,University of Barcelona | Llasat M.C.,University of Barcelona | Quintana-Segui P.,Observatori de lEbre | Turco M.,University of Barcelona
Science of the Total Environment | Year: 2018

In this paper, we have compared different bias correction methodologies to assess whether they could be advantageous for improving the performance of a seasonal prediction model for volume anomalies in the Boadella reservoir (northwestern Mediterranean). The bias correction adjustments have been applied on precipitation and temperature from the European Centre for Middle-range Weather Forecasting System 4 (S4). We have used three bias correction strategies: two linear (mean bias correction, BC, and linear regression, LR) and one non-linear (Model Output Statistics analogs, MOS-analog). The results have been compared with climatology and persistence. The volume-anomaly model is a previously computed Multiple Linear Regression that ingests precipitation, temperature and in-flow anomaly data to simulate monthly volume anomalies. The potential utility for end-users has been assessed using economic value curve areas. We have studied the S4 hindcast period 1981–2010 for each month of the year and up to seven months ahead considering an ensemble of 15 members. We have shown that the MOS-analog and LR bias corrections can improve the original S4. The application to volume anomalies points towards the possibility to introduce bias correction methods as a tool to improve water resource seasonal forecasts in an end-user context of climate services. Particularly, the MOS-analog approach gives generally better results than the other approaches in late autumn and early winter. © 2017 Elsevier B.V.

Perez-Zanon N.,Rovira i Virgili University | Casas-Castillo M.C.,Polytechnic University of Catalonia | Rodriguez-Sola R.,Polytechnic University of Catalonia | Pena J.C.,Servei Meteorologic de Catalonia | And 3 more authors.
Theoretical and Applied Climatology | Year: 2015

The relationship between maximum rainfall rates for time intervals between 5 min and 24 h has been studied from almost a century (1905–2003) of rainfall data registered in the Ebre Observatory (Tarragona, Spain). Intensity–duration–frequency (IDF) curves and their master equation for every return period in the location have been obtained, as well as the probable maximum precipitation (PMP) for all the considered durations. In particular, the value of the 1-day PMP has resulted to be 415 mm, very similar to previous estimations of this variable for the same location. Extreme rainfall events recorded in this period have been analyzed and classified according to their temporal scale. Besides the three main classes of cases corresponding to the main meteorological scales, local, mesoscale, and synoptic, a fourth group constituted by complex events with high-intensity rates for a large range of durations has been identified also, indicating the contribution of different scale meteorological processes acting together in the origin of the rainfall. A weighted intensity index taking into account the maximum rainfall rate in representative durations of every meteorological scale has been calculated for every extreme rainfall event in order to reflect their complexity. © 2015 Springer-Verlag Wien

Escorihuela M.J.,IsardSAT | Merlin O.,CNRS Center for the Study of the Biosphere from Space | Escorihuela A.,IsardSAT | Quintana P.,Observatori de lEbre | Martinez D.,PildoLabs
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2012

The objective of the SMOScat project is to operationally provide soil moisture at 1 km resolution or better over Catalonia. A downscaling algorithm is applied to 40 km resolution L2 SMOS (Soil Moisture and Ocean Salinity) soil moisture product using 1 km resolutionMODIS (MODerate resolution Imaging Spectroradiometer) data. High resolution soil moisture is compared with in situ measurements collected each month from April to October 2011 in a dryland and irrigated area. Our results show and increase of correlation coefficient with in-situ measurements when high resolution soil moisture is used. The 2012 experimental field campaign will address topography issues. © 2012 IEEE.

Llasat M.C.,University of Barcelona | Marcos R.,University of Barcelona | Llasat-Botija M.,University of Barcelona | Gilabert J.,University of Barcelona | And 2 more authors.
Atmospheric Research | Year: 2014

The present paper shows an in-depth analysis of the evolution of floods and precipitation in Catalonia for the period 1981-2010. In order to have homogeneous information, and having in mind that not gauge data was available for all the events, neither for all the rivers and stream flows, daily press from a specific newspaper has been systematically analysed for this period. Furthermore a comparison with a longer period starting in 1900 has been done. 219 flood events (mainly flash flood events) have been identified for the period of 30. years (375 starting in 1900), 79 of them were ordinary, 117 of them were extraordinary and 23 of them were catastrophic, being autumn and summer the seasons with the maxima values. 19% of the events caused a total of 110 casualties. 60% of them died when they tried to cross the street or the stream. Factors like the evolution of precipitation, population density and other socio-economical aspects have been considered. The trend analysis shows an increase of 1 flood/decade that probably has been mainly due to inter-annual and intra-annual changes in population density and in land-use and land-cover. © 2014 Elsevier B.V.

Turco M.,University of Barcelona | Quintana-Segui P.,Observatori de lEbre | Llasat M.C.,University of Barcelona | Herrera S.,Institute Fisica Of Cantabria | Gutierrez J.M.,Institute Fisica Of Cantabria
Journal of Geophysical Research: Atmospheres | Year: 2011

Model Output Statistics (MOS) has been recently proposed as an alternative to the standard perfect prognosis statistical downscaling approach for Regional Climate Model (RCM) outputs. In this case, the model output for the variable of interest (e.g. precipitation) is directly downscaled using observations. In this paper we test the performance of a MOS implementation of the popular analog methodology (referred to as MOS analog) applied to downscale daily precipitation outputs over Spain. To this aim, we consider the state-of-the-art ERA40-driven RCMs provided by the EU-funded ENSEMBLES project and the Spain02 gridded observations data set, using the common period 1961-2000. The MOS analog method improves the representation of the mean regimes, the annual cycle, the frequency and the extremes of precipitation for all RCMs, regardless of the region and the model reliability (including relatively low-performing models), while preserving the daily accuracy. The good performance of the method in this complex climatic region suggests its potential transferability to other regions. Furthermore, in order to test the robustness of the method in changing climate conditions, a cross-validation in driest or wettest years was performed. The method improves the RCM results in both cases, especially in the former. Copyright 2011 by the American Geophysical Union.

Adame J.A.,National Institute for Aerospace Technology INTA | Sole J.G.,Observatori de lEbre
Atmospheric Pollution Research | Year: 2013

The aim of this paper is to study the levels and variability of surface ozone in the lower Ebre Valley and to estimate whether this surface ozone has its origin in local photochemical processes or in long-range transport. Surface ozone data series of twelve years (1994-2005) have been used from a rural area (Ebre Observatory) together with three years (2003-2005) data of nitrogen dioxide (NO2). Ozone trends over the whole seasonal period, weekly and daily variations and exceedances of the legal threshold have been investigated. Furthermore, a representative ozone event has been studied in detail. Using ozone data from the twelve-year period resulted in a positive trend with an increase of 2.18 μg m-3 year-1 and 0.64 μg m-3 year-1 in summer and winter, respectively. The seasonal evolution of ozone gives a minimum value in winter and a maximum higher than 75 μg m-3 associated with the minimum values of NO2. Ozone-NO2 variation shows a weak ozone increase on weekdays and a small decrease in NO2 concentrations at the weekends. Hence, a weekend effect is not observed. Ozone and NO2 concentrations show a diurnal pattern with NO2 peaks both in the early morning and in the evening, and maximum ozone concentrations, higher than 90-100 μg m-3, from 12:00 to 18:00 UTC in the warmer seasons. The threshold for the protection of human health has been exceeded from March to September each year, with a mean of 33 times per year. An event with high ozone levels originated by transport processes from the Mediterranean area was also analysed. The results suggest that high ozone could be caused mainly by transport mechanisms, and the Ebre valley could be considered to be a natural communication channel between the western Mediterranean basin and the Atlantic Ocean. © Author(s) 2012.

Gaite B.,CSIC - Institute of Earth Sciences Jaume Almera | Ugalde A.,CSIC - Institute of Earth Sciences Jaume Almera | Villasenor A.,CSIC - Institute of Earth Sciences Jaume Almera | Blanch E.,Observatori de lEbre
Physics of the Earth and Planetary Interiors | Year: 2016

On September 2013, increased seismic activity was recorded near the CASTOR offshore underground gas storage (UGS), in the Gulf of Valencia (Spain). According to the reports by the Spanish Instituto Geográfico Nacional (IGN), more than 550 events occurred during two months, the strongest having a magnitude of Mw = 4.2 which took place two weeks after the gas injection stopped. The low magnitude of the events (with only 17 earthquakes having mbLg greater than 3), the lack of nearby stations, and the inhomogeneous station distribution made the location problem a great challenge. Here we present improved locations for a subset of 161 well recorded events from the earthquake sequence using a probabilistic nonlinear earthquake location method. A new 3-D shear-wave velocity model is also estimated in this work from surface-wave ambient noise tomography. To further improve the locations, waveform cross-correlations are computed at each station for every event pair and new locations are obtained from an inverted set of adjusted travel time picks. The resulting hypocentral solutions show a tighter clustering with respect to the initial locations and they are distributed in a NW-SE direction. Most of the earthquakes are located near the injection well at depths of about 6 km. Our results indicate that the observed seismicity is closely associated with the injection activities at the CASTOR underground gas storage and may have resulted from the reactivation of pre-existing unmapped faults, located a few kilometers below the reservoir. © 2016 Elsevier B.V.

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