Seismic Activity Rates in the Iberian Península (original) (raw)
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Seismic Hazard Estimate at the Iberian Peninsula
Pure and Applied Geophysics, 2002
Seismic hazard at the Iberian Peninsula has been evaluated by using a methodology which combines both zonified and non-zonified probabilistic methods. Seismic sources are used when considering zones where certain calculation parameters may be considered homogeneous, as in zonified methods, while, on the other hand, earthquakes are considered wherever it has taken place, as in non-zonified methods. The methodology which is applied in this paper has been originally used to calculate the seismic hazard maps in the United States. In our case, it has been necessary to adapt the method to the specific features of the seismicity in the Iberian Peninsula and its geographical surroundings, not only with respect to its distribution and characteristics, but also with respect to the properties of the seismic catalog used. Geographically, the main feature of the result is the fact that it reflects both historical seismicity and current seismic clusters of the region. Despite the smoothing, maps show marked differences between several seismic zones; these differences becoming more noticeable as exposure time increases. Maximum seismic hazard is found to be in the southwestern region of the Peninsula, especially in the area of the Cape St. Vicent, and around Lisbon. The uncertainty of the results, without considering that due to the attenuation laws, as deduced from the other evaluation parameters, is quite stable, being more sensitive to the parameters b and m max of the Gutenberg-Richter relation.
Towards a new seismic hazard assessment in Spain
2010
Seismic hazard is an evolving science that is fed by geological and seismological studies. As new data and models arise, the revision of hazard maps is compelling. Additionally, understanding the nature and the sources of the uncertainties involved in seismic hazard analyses is essential in order to reduce them. In this context, Spain is not an exception and a move towards a reassessment of the national hazard maps is pertinent. Several hazard-controlling factors needing to be updated and eventually revaluated are identified in this work in progress. The first one concerns the seismic catalogue. It must be homogenised, incorporating data from neighbouring countries and correlating magnitude scales for different regions and recording periods. A second factor refers to seismicity characterization by zoning and zoneless models: Neotectonic, seismological and other geological data that justify the development of a new zoning model for Spain and adjacent areas are disclosed. Revaluation of seismic areas that are traditionally considered as stable but show evidence of seismic activity at present and during Quaternary times needs to be considered. The interest of developing a neotectonic characterization of active faults is advanced. For zoneless models, the different elements that define the continuous spatial variation of the activity rate density have to be examined. For a zoneless model based on kernel functions, these elements would be the specific type of kernel function, the bandwidth and the reference years. A third factor requiring a modern analysis refers to the implementation of different strong motion prediction models. These include models based on local data and developed with data from other regions. Special attention is paid to the application of the next generation attenuation models originally developed for western North America to Spain. Criteria for selecting different models must be clearly and thoughtfully enumerated. The final goal of this work is to assess the variability of seismic hazard results to the new data and models that are becoming available. Such information will be of indubitable interest for forthcoming versions of the seismic code, national annexes of Eurocode 8 and research projects fomented by the Spanish Nuclear Security Council.
Engineering Geology, 2005
A preliminary probabilistic seismic hazard assessment in terms of Arias intensity is presented for the first time in southeastern Spain. In the calculation, the spatially smoothed seismicity procedure has been used, considering four seismic models, and a seismic catalog updated up to 1999. One of the models that include the most significant seismicity, considers earthquakes above 5.5 M S in the last 700 years.
Mapping of seismic parameters of the Iberian Peninsula by means of a geographic information system
Central European Journal of Operations Research, 2017
In this paper, the following seismic parameters, the maximum recorded magnitude (M max), the Gutenberg-Ritcher b-value and the (normalized) mean seismic activity rate, AR, have been calculated for the Iberian Peninsula and surroundings. A geographic information system has been employed to compile all data, to work with different geographic systems and to generate the maps. An improved version of the National Geographic Institute of Spain earthquake catalog has been considered as input. Due to the detection network evolution and the extent of the territory, completeness values must be sectored to obtain reliable b-values and AR values. So, a previous work on regionalization has been considered. First, a working catalog has been elaborated. To do so, the size of some shocks through specific studies have been reviewed, magnitudes have been converted to moment magnitude (M w) and dependent events have been removed. Second, for the b-value and the AR calculation a method that considers inhomogeneous catalogs, different magnitudes and various years of B F. Martínez-Álvarez
A New Seismic Hazard Assessment in the Region of Andalusia (Southern Spain)
2010
A probabilistic seismic hazard assessment of Andalusia (Southern Spain) in terms of peak ground acceleration, PGA, and spectral accelerations, SA(T), is presented in this paper. In contrast to most of the previous studies in the region, which were performed for PGA, making use of Intensity-to-PGA relationships, hazard was here calculated in terms of magnitude, using published spectral ground-motion models. Moreover, we considered different ground-motion models for the Atlantic sources, since the attenuation of those motions seems to be slower, as evidenced in the case of the extensive macroseismic areas of earthquakes like those occurred in the years 1755, 1969 and 2007. A comprehensive review of the seismic catalogue and of the seismogenic models proposed for the region was carried out, including those for Northern Africa, which is part of the influence area. Hazard calculations were performed following the Probabilistic Seismic Hazard Assessment (PSHA) methodology using a logic tree, which accounts for six different seismic source zonings and five different ground-motion attenuation relationships. Hazard maps in terms of PGA and SA (0.2 s) and SA (1 s) and coefficient of variation (COV) maps, for the 475-year return period were first obtained in rock sites. A geotechnical classification and amplification factors were proposed and new hazard maps including local effects were represented, showing PGA values ranging from 24 to 370 cm/s 2 for the whole Andalusian territory, with the highest expected values (PGA > 300 cm/s 2 ) in some parts of the Granada Province and in the town of Vélez Málaga. Lowest values (PGA < 50 cm/s 2 ) correspond to some towns of the Huelva
A deterministic seismic risk macrozonation of Seville
Arabian Journal of Geosciences
The seismicity of the southwestern Iberian Peninsula is moderate but large events with long return periods occur (≈ 200 years). This exceeds the life of various generations, making the population unacquainted with the seismic hazard. On the one hand, this results in a low demanding seismic code which increases the seismic vulnerability and, therefore, the seismic risk. On the other hand, the local emergency services must be properly prepared to face a destructive seismic event, with emergency plans and mitigation strategies. This assumption enhances the need of assessing the seismic risk of Seville in a civil protection context. For all the aforementioned and for the lack of instrumental data of relevant earthquakes, the assessment of the seismic hazard in this area is challenging. To do this, seismogenic zones of the new seismic hazard map of Spain have been used as sources. The peak ground acceleration (PGA) for each scenario has been calculated by means of ground motion predictio...
Testing the Earthquake Early-Warning Parameter Correlations in the Southern Iberian Peninsula
Pure and Applied Geophysics, 2015
The south of the Iberian Peninsula is of especial interest for the application of Earthquake Early Warning System (EEWS) technologies due to the past occurrence of damaging earthquakes such as the 1755 Lisbon earthquake. However, there are several critical issues that need to be addressed in order to develop an EEWS in this area. The first is the magnitude scale inhomogeneity of the available catalogues. A second is that most of the available broad-band seismograms for this area correspond to earthquakes with magnitudes less than 6.0, recorded at distances greater than 100 km, and sometimes with a low signal-to-noise ratio. And third, the occurrence of large earthquakes in this area means that the standard EEWS time window normally used needs to be tested in order to check whether it is long enough. Our paper describes the results of homogenizing the catalogue magnitudes by using empirical relationships to obtain the moment magnitude M w. A criterion based on a threshold value for the signal-to-noise ratio is applied in order to avoid noise-contaminated seismogram data. An important part of the study is a check of whether the correlations previously obtained for south Iberia are valid for other neighbouring areas such as Algeria, and for larger earthquakes. Finally, since recent studies have shown that the larger the earthquake the longer the time window needed to properly estimate the magnitude, the window was increased progressively from 0 to 20 s in order to study the behaviour of the EEWS parameters for the largest earthquakes in the database.