The European Archive of Historical Earthquake Data (AHEAD): compilation, results, and perspectives.

Historical seismic catalogues in Europe have been mostly compiled on a national basis starting from historical data collected and interpreted according to different procedures and varied levels of formalization. With few exceptions, the macroseismic data that stand behind the catalogues are not available, or simply never existed. The present-day knowledge on past seismicity in Europe is consequently far from being homogeneous. This situation affected the past efforts for the compilation of homogeneous, continent-wide catalogues and still restrains the ongoing initiatives on this topic. To overcome this situation, the NERIES NA4 project realized the European Archive of Historical Earthquake Data (AHEAD). AHEAD collects and puts together in a critical way the background information supporting European earthquakes between the years 1000 and 1963. The collected information consists of the most significant, or recent, material supporting an earthquake, such as: i) studies that interpret the historical records in terms of Macroseismic Data-Points (MDPs); ii) studies that provide the historical records but not interpreted in terms of MDPs; iii) parameters from catalogues, only. AHEAD contains entries related to more than 10.000 earthquakes, and the inventoried material is made available through the web. It also provides in a standardized database the MDPs that support about the 60% of the listed earthquakes. For a large number of them such MDPs have been released for the first time by partner institutions in the framework of NERIES NA4. AHEAD is conceived as an interactive tool for representing and improving the knowledge on historical earthquakes, with the aim of making it homogeneous at a European level. Through the archive researchers can easily: 1) trace back the information supporting each earthquake in order to reappraise and improve the knowledge of it; 2) compare the different studies on each earthquake and select a preferred one. This is, for example, the procedure followed for the selection of data upon which the NERIES NA4 European Earthquake Catalogue has been compiled. 3) help keeping the archive as much up-to-date as possible, commenting studies, data, and parameters and feeding it with fresh studies.UnpublishedMontpellier (France)5.1. TTC - Banche dati e metodi macrosismiciope

The European Archive of Historical Earthquake Data (AHEAD): compilation, results, and perspectives.

Historical seismic catalogues in Europe have been mostly compiled on a national basis starting from historical data collected and interpreted according to different procedures and varied levels of formalization. With few exceptions, the macroseismic data that stand behind the catalogues are not available, or simply never existed. The present-day knowledge on past seismicity in Europe is consequently far from being homogeneous. This situation affected the past efforts for the compilation of homogeneous, continent-wide catalogues and still restrains the ongoing initiatives on this topic. To overcome this situation, the NERIES NA4 project realized the European Archive of Historical Earthquake Data (AHEAD). AHEAD collects and puts together in a critical way the background information supporting European earthquakes between the years 1000 and 1963. The collected information consists of the most significant, or recent, material supporting an earthquake, such as: i) studies that interpret the historical records in terms of Macroseismic Data-Points (MDPs); ii) studies that provide the historical records but not interpreted in terms of MDPs; iii) parameters from catalogues, only. AHEAD contains entries related to more than 10.000 earthquakes, and the inventoried material is made available through the web. It also provides in a standardized database the MDPs that support about the 60% of the listed earthquakes. For a large number of them such MDPs have been released for the first time by partner institutions in the framework of NERIES NA4. AHEAD is conceived as an interactive tool for representing and improving the knowledge on historical earthquakes, with the aim of making it homogeneous at a European level. Through the archive researchers can easily: 1) trace back the information supporting each earthquake in order to reappraise and improve the knowledge of it; 2) compare the different studies on each earthquake and select a preferred one. This is, for example, the procedure followed for the selection of data upon which the NERIES NA4 European Earthquake Catalogue has been compiled. 3) help keeping the archive as much up-to-date as possible, commenting studies, data, and parameters and feeding it with fresh studies.UnpublishedMontpellier (France)5.1. TTC - Banche dati e metodi macrosismiciope

Full microtremor H/V(z, f) inversion for shallow subsurface characterization

The H/V spectral ratio has emerged as a single station method within the seismic ambient noise analysis field by its capability to quickly estimate the frequency of resonance at a site and through inversion the average profile information. Although it is easy to compute from experimental data, its counter theoretical part is not obvious when building a forward model which can help in reconstructing the derived H/V spectrum. This has led to the simplified assumption that the noise wavefield is mainly composed of Rayleigh waves and the derived H/V often used without further correction. Furthermore, only the right (and left) flank around the H/V peak frequency is considered in the inversion for the subsurface 1-D shear wave velocity profile. A new theoretical approach for the interpretation of the H/V spectral ratio has been presented by Sanchez-Sesmaet al. In this paper, the fundamental idea behind their theory is presented as it applies to receivers at depth. A smooth H/V(z, f) spectral curve on a broad frequency range is obtained by considering a fine integration step which is in turn time consuming. We show that for practical purposes and in the context of inversion, this can be considerably optimized by using a coarse integration step combined with the smoothing of the corresponding directional energy density (DED) spectrum. Further analysis shows that the obtained H/V(z, f) spectrum computed by the mean of the imaginary part of Green's function method could also be recovered using the reflectivity method for a medium well illuminated by seismic sources. Inversion of synthetic H/V(z, f) spectral curve is performed for a single layer over a half space. The striking results allow to potentially use the new theory as a forward computation of the H/V(z, f) to fully invert the experimental H/V spectral ratio at the corresponding depth for the shear velocity profile (Vs) and additionally the compressional velocity profile (Vp) using receivers both at the surface and in depth. We use seismic ambient noise data in the frequency range of 0.2-50 Hz recorded at two selected sites in Germany where borehole information is also available. The obtained 1-D Vs and Vp profiles are correlated with geological log information. Results from shallow geophysical experiment are also used for comparison