Abstract
Abstract. Macroseismic intensity is a parameter of the severity of ground movement evaluated in terms of the effects that earthquakes produce on people, buildings and the environment, constituting an extremely important information source for the seismologist and engineer of structures. In recent studies, the authors of this study published a new map of maximum intensities observed for continental Portugal considering all observations of macro-seismic intensity higher than III relative to earthquakes occurred between 1344 and 2015 (Teves-Costa et al., 2019). In each parish and municipality of the continental part of the country, the maximum values of intensity were defined. A map of maximum intensities produced in this way was essentially controlled by earthquakes of greater intensity, the 1909.04.23 (near-field) and 1755.11.01 (far-field) earthquakes. In the present work, a spatial distribution of the earthquakes presents in the database (classified by their nature - near-field or far-field - intensity, and epoch) are analysed. The spatial structure, which allows the detection of spatial dependence or autocorrelation of intensity values is also explored in this work, in order to identify regions with similar macroseismic characteristics. The combination of the map of maximum intensities and the products generated in this work are essential for the authorities as a base of support in the definition of joint adaptation strategies for the various regions of the territory, as well as contribute to a better management of the emergency system in Portugal.
Highlights
1.1 Geodynamic frameworkThe geodynamic framework of Portugal mainland is dominated by the collision between the Nubian and Eurasian plates which occurs at a very slow speed of ~ 4 mm / year
The seismic cycles associated with active faults are very long and seismic hazard assessment studies should consider the historical seismicity of Portugal mainland as an undoubted source of information
While in the study of the maximum intensities the authors defined a methodology to spatialize maximum intensity values, which results were concretized in a set of maps representing the worst-case scenarios on the basis of the historical seismicity of almost 700 years, the present study explores the same data catalogue but aims to spatialize seismic intensities which reveals lower intensities values but higher frequencies of occurrence
Summary
The geodynamic framework of Portugal mainland is dominated by the collision between the Nubian and Eurasian plates which occurs at a very slow speed of ~ 4 mm / year. The consequent tectonic activity, that extends in an emerging region, leading to a slow deformation regime in the continental Portuguese territory. Despite the existence of moderate seismic activity, due to this geotectonic context, earthquakes of high magnitude occur as well, such was the 1st November 1755 Lisbon earthquake with an estimated magnitude of Mw 8.5-8.7. The last strong earthquake that affected the territory of Portugal mainland occurred on February 28, 1969 (M≈8.0). The earthquake of 1969.02.28 was felt throughout the continental territory with intensities between IV and VIII (MM56). In the SW region of Portugal, it produced the collapse of some houses and in Lisbon (intensity V-VI) some chimneys fell
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