Statistical analysis of different seismogenic zonings of the Iberian Peninsula and adjacent areas through a Geographic Information System

Resumo

The knowledge of the seismic hazard in the Iberian Peninsula (IP) and its neighboring area is important to address the mitigation of damage that earthquakes could cause in it. The occurrence of earthquakes in the area is quite frequent because it is in the contact zone between the Eurasian Plate and the African Plate. The general objective of this document is the calculation, representation and analysis of a set of seismic parameters (b-value, maximum magnitude and annual rate of earthquakes per unit area) of the Iberian Peninsula and its adjacent area, considering geographic information systems (GIS) as a basic working tool. These systems allow the integration of data from different information sources, as well as rigorous and quality analysis and graphical representations. To achieve this goal, having a quality seismic catalog is essential. Therefore, one has been compiled for the area as complete, rigorous and extensive in the time possible, and further, revised, homogeneous in size (magnitude) and with independent events. This has served as the basis for the works exposed here. For the generation of this catalog, the database of earthquakes of the National Geographic Institute of Spain has been consider as a starting point, that has been revised (especially the magnitude) and completed with other databases and specific studies. In addition, the catalog of work has included earthquakes for which only macroseismic (and reliable) information is available as well as those recorded during the instrumental period according to the scientific advances of each moment. Then, the size of all the events has been transformed to moment magnitude (Mw) in order to compare it, taking into account only the events with Mw greater or equal to 3.0. Subsequently, a process of elimination of non-main shocks (foreshocks, aftershocks and swarms) has been carried out. Finally, a completeness date has been considered for each magnitude. In this thesis, the b-value, the annual rate of earthquakes per unit area and the maximum magnitude have been calculated, represented and analyzed. In addition, it has been done through two approaches. The first deals with zoning related to Spanish seismic regulations and are based on both geological characteristics and seismicity of the area; and others that are based on objective and mathematically robust criteria and considers only seismicity. In the second approach, a set of multiresolution grids have been established, in which zonings are defined according to a purely geographic criterion. The size of the cells (zones) has been 0.5º x 0.5º for the calculation of the maximum magnitude recorded and 1º x 1º and 2º x 2º for the b-value and the annual rate normalized with the area. In both types of zoning, after the calculations and the representation of the seismic parameters, an analysis of them has been carried out. From this analysis it can be deduced that in some areas there has not been a quantity of events that allows to derive seismic parameters with solidity from a statistical point of view. It can also be concluded that earthquakes with maximum recorded magnitude have a marine epicenter and are located in the SW of the IP. Moreover, the b-value takes a value of 1.0 or somewhat lower in the contact zone between the Eurasian and African plates (a value that decreases further to the east), while in the mainland, 1.2 can be considered an approximate value, with somewhat higher values in some areas. Finally, regarding the annual rate, it should be noted that the highest values (close to 1E-3 events / km2) appear in the Granada basin and in the Pyrenees Region and to a lesser extent, to the SW of Cabo de San Vicente, in Galicia and a large part of the southeast of the IP where values greater than 1E-4 are exceeded.