Bergamo, Paolo

This paper reports on site characterization for a set of accelerometric stations of the RAN (Italian accelerometric network) with specific attention to the shear wave velocity profile. The latter is indeed of primary importance for the usability of the accelerometric database. Surface wave analysis has been chosen as the primary investigation method since it offers the possibility of reaching the required accuracy with reasonable costs. A range of different techniques, both of the active-source and passive-source types, has been adopted to cope with the objectives of the characterization in relation to specific geological settings. Quality assessment of experimental data has been implemented to check the consistency of the measurements also with respect to the fundamental hypotheses of the method. Strategies to improve the reliability and robustness of the surface wave data inversion were exploited in order to mitigate problems arising from solution non-uniqueness and influence of higher modes in the propagation. Comparisons with independent borehole tests, available at some specific sites, confirm the reliability of the results. Although the research program covered only a subset of the network, the obtained results show the importance of specific experimental investigations aimed at estimating the shear wave velocity profile. Indeed the results lead to a re-classification of several sites with respect to the preliminary classification based on surface geology. Within this context, four selected case histories are reported in the present paper.

Setting-up standard practices, together with a clear evaluation of their quality, are becoming very important to reach high-level sitecharacterization metadata, useful for site effects studies, seismic microzonation, seismic hazard assessment and many other research fields. In the last years, several efforts have been done at national and international level to define standards and guidelines for seismic site characterization (e.g., Foti et al., Bull Earthquake Eng, 2017, doi:10.1007/s10518-017-0206-7; Geological Survey of Canada, Open File 7078, 2012, doi:10.4095/291753; Consortium of Organizations for Strong Motion Observation Systems, http://www.cosmos-eq.org; WP12- Deliverable D23.12, SESAME European research project, 2004). Within the 2017-2020 activities of the “Networking databases of site and station characterization” (WP7-NA5 of the SERA “Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe” Horizon 2020 Project), European teams are working on the best practice for site characterization and related quality assessment target to network operators and seismological and engineering communities. More specifically, the goals of this task are: (i) to evaluate the most relevant site effects indicators; (ii) to write practical guidelines for site effects characterization and related site condition parameters at rock sites (including topography effects) and soft soils (including non-linear and basin effects); (iii) to propose a quality metrics on the site characterization parameters. As a first step, we have prepared a Questionnaire for collecting existing bibliography and best practice schemes to compute indicators for site effects characterization. We sent the Questionnaire to selected research groups of different countries, both partners of the SERA project (ISTERRE-CNRS, France; ETH, Switzerland; INGV, Italy; AUTH, Greece) and several external groups involved in site characterization (Caltech-USGS, USA; AFAD, Turkey; Virginia Tech USA; GFZ, Germany; ITSAK, Greece; University of Potsdam, Germany; UoTUniversity of Texas, USA; INGV, Italy), and collected back the answers. Each team provided the list of site effects indicators, their importance for site effects assessment (based on expert judgment) and their preferred methods of analysis for retrieving the indicators. In the Questionnaire, the site-effect indicators were grouped into (i) Scalar (e.g. resonance frequency), (ii) Depthdependent (e.g. shear-wave Vs profile), (iii) Frequency-dependent (e.g. spectral ratio), (iv) Geological/Morphological (e.g. Surface geology/lithology unit) and (v) Advanced siteeffects (e.g. numerical 2D or 3D modeling) parameters. Each indicator is described through several fields, summarized into five main subsets: Importance - in-depth index related to the amount of knowledge on site-effects characterization supplied by each indicator, and it can assume three values (basic, intermediate and top), depending on the expert judgment; Feasibility - level of difficulty to measure the target indicator (easy, average and difficult); Data - type of data used to measure the proposed indicator; Analysis - method of analysis and suggested code to derive the indicator, including the value’s selection and uncertainty estimation; Bibliography - references and guidelines related to the best practice of measurement and analysis. A preliminary analysis of the Questionnaires reveals a consensus on several basic indicators, such as the resonance frequency, Vs30 or the 1D Vs profile, even if the teams use different data acquisition, analysis methods and metrics. Fewer teams indicated more advanced parameters, such as 2D-3D site goals of this task are: (i) to evaluate the most relevant site effects indicators; (ii) to write practical guidelines for site effects characterization and related site condition parameters at rock sites (including topography effects) and soft soils (including non-linear and basin effects); (iii) to propose a quality metrics on the site characterization parameters. As a first step, we have prepared a Questionnaire for collecting existing bibliography and best practice schemes to compute indicators for site effects characterization. We sent the Questionnaire to selected research groups of different countries, both partners of the SERA project (ISTERRE-CNRS, France; ETH, Switzerland; INGV, Italy; AUTH, Greece) and several external groups involved in site characterization (Caltech-USGS, USA; AFAD, Turkey; Virginia Tech USA; GFZ, Germany; ITSAK, Greece; University of Potsdam, Germany; UoTUniversity of Texas, USA; INGV, Italy), and collected back the answers. Each team provided the list of site effects indicators, their importance for site effects assessment (based on expert judgment) and their preferred methods of analysis for retrieving the indicators. In the Questionnaire, the site-effect indicators were grouped into (i) Scalar (e.g. resonance frequency), (ii) Depthdependent (e.g. shear-wave Vs profile), (iii) Frequency-dependent (e.g. spectral ratio), (iv) Geological/Morphological (e.g. Surface geology/lithology unit) and (v) Advanced siteeffects (e.g. numerical 2D or 3D modeling) parameters. Each indicator is described through several fields, summarized into five main subsets: Importance - in-depth index related to the amount of knowledge on site-effects characterization supplied by each indicator, and it can assume three values (basic, intermediate and top), depending on the expert judgment; Feasibility - level of difficulty to measure the target indicator (easy, average and difficult); Data - type of data used to measure the proposed indicator; Analysis - method of analysis and suggested code to derive the indicator, including the value’s selection and uncertainty estimation; Bibliography - references and guidelines related to the best practice of measurement and analysis. A preliminary analysis of the Questionnaires reveals a consensus on several basic indicators, such as the resonance frequency, Vs30 or the 1D Vs profile, even if the teams use different data acquisition, analysis methods and metrics. Fewer teams indicated more advanced parameters, such as 2D-3D site

Site characterization is a key input in seismic hazard and risk assessment (e.g. Ground Motion Prediction Equation, microzonation studies, damage scenarios) and seismic design (building codes, critical facilities). Although the number of strong-motion stations in free-field and engineering structures has largely increased over the world in the last twenty years, only a limited number of sites includes detailed site condition indicators: mostly geology and EC8 soil class, more rarely shear-wave velocity (Vs) information (e.g. Vs30 and Vs profiles), without proper documentation and quality assessment in most cases. This lack of information is a critical issue, e.g. for deriving reference rock/soil velocity profiles for region-specific GMPEs, site-specific hazard assessment, vs-kappa adjustments, seismic response of engineering infrastructures, risk modeling at urban or regional scale. Within the framework of the SERA “Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe” Horizon 2020 Project, a networking activity has been set up to propose a comprehensive European strategy and standards fostering site characterization of seismic stations in Europe. We will present the status of this networking activity that focuses on several issues. The first target is to evaluate the most relevant site characterization scalar, depth and frequencydependant indicators (e.g. Vs30, resonance period, velocity profiles, kappa, amplification factors and functions, etc.) for seismic hazard purposes and, thereafter, to propose best practice for site characterization together with standards for overall quality metrics on site characterization. The second target focuses on disseminating, within the broader seismological and engineering community, site characterization metadata developed within the EU NERA and EPOS-IP projects in order to validate and/or further develop metadata format schemes for wide use. Based on available site characterization information in Europe and considering the research and engineering needs, the third target proposes to set up a road map to prioritize strong motion site characterization in Europe for the next decade. Finally, a task is dedicated to investigate relevance of new site condition and amplification proxies (for example combining resonance frequency, local slope and other parameters, proxy for non-linear effects, wavelength-scaled curvature and topographic position index position as proxies for topographic effects, aggravation factor for basin effects, etc.) and their implementation at the European scale and into site characterization metadata.