Dept. of Structural Engineering, Politecnico di Milano

This report summarizes the seismicity in Switzerland and surrounding regions in the years 2015 and 2016. In 2015, the Swiss Seismological Service detected and located 735 earthquakes in the region under consideration. With a total of 20 earthquakes of magnitude ML C 2.5, the seismic activity of potentially felt events in 2015 was close to the average of 23 earthquakes over the previous 40 years. Seismic activity was above average in 2016 with 872 located earthquakes of which 31 events had ML C 2.5. The strongest event in the analyzed period was the ML 4.1 Salgesch earthquake, which occurred northeast of Sierre (VS) in October 2016. The event was felt in large parts of Switzerland and had a maximum intensity of V. Derived focal mechanisms and relative hypocenter relocations of aftershocks image a SSE dipping reverse fault, which likely also hosted an ML 3.9 earthquake in 2003. Another remarkable earthquake sequence in the Valais occurred close to Sion with four felt events (ML 2.7–3.2) in 2015/16. We associate this sequence with a system of WNW-ESE striking fault segments north of the Rhoˆne valley. Similarities with a sequence in 2011, which was located about 10 km to the NE, suggest the existence of an en-echelon system of basement faults accommodating dextral slip along the Rhoˆne-Simplon line in this area. Another exceptional earthquake sequence occurred close to Singen (Germany) in November 2016. Relocated hypocenters and focal mechanisms image a SW dipping transtensional fault segment, which is likely associated with a branch of the Hegau-Bodensee Graben. On the western boundary of this graben, micro-earthquakes close to Schlattingen (TG) in 2015/16 are possibly related to a NE dipping branch of the Neuhausen Fault. Other cases of earthquakes felt by the public during 2015/16 include earthquakes in the region of Biel, Vallorcine, Solothurn, and Savognin.

Here we present first results of a joint effort undertaken in ongoing European project NERA -JRA1, which aims at establishing scientifically solid and practically acceptable propositions to incorporate surface topography effects in seismic hazard estimates. We assembled a dataset of both ambient vibration and earthquake recordings acquired at 40 European sites with pronounced topography. It comprises a wide variety of sites including populated hills and even extreme cases of unstable rock slopes in Alpine regions. Results of the polarisation analysis for the two sites presented here show the peculiarity of the topographic site effects.

Skip Nav Destination RESEARCH ARTICLE| APRIL 07, 2021 Preface to the Focus Section on European Seismic Networks and Associated Services and Products Carlo Cauzzi; Susana Custódio; Christos P. Evangelidis; Giovanni Lanzano; Lucia Luzi; Lars Ottemöller; Helle Pedersen; Reinoud Sleeman Seismological Research Letters (2021) 92 (3): 1483–1490. https://doi.org/10.1785/0220210055 Article history Standard View PDF LinkPDF Cite Share Icon Share Tools Icon Tools Observational seismology in Europe is firmly rooted in national and regional observatories in charge of managing more than 100 permanent seismic networks and more than 200 past and present temporary deployments. Primarily driven by governmental mandates to detect local seismicity and provide earthquake information to civil protection agencies and the general public, this monitoring effort also results in a tremendous amount of high‐quality data—more than 12,000 stations presently contribute to the European Integrated Data Archive (EIDA)—which is made available to scientists and practitioners. This lively community of seismic data providers and users is at the core of the success of this focus section: 30 groups responded enthusiastically to our call for papers, providing high‐quality contributions that describe the state of the art in observational seismology in the greater European region, addressing all components of the life cycle of seismic data, from station design to open dissemination of data and seismological products (Amato et al., 2021; Bono et al., 2021; Bragato et al., 2021; Büyükakpınar et al., 2021; Cambaz et al., 2021; Carrilho et al., 2021; Danecek et al., 2021; Evangelidis et al., 2021; Galea et al., 2021; Heit et al., 2021; Lanzano et al., 2021; Lenhardt et al., 2021; Lund et al., 2021; Mărmureanu et al., 2021; Margheriti et al., 2021; Masson et al., 2021; Mader and Ritter, 2021; Ottemöller et al., 2021; Quinteros, Strollo,et al., 2021; Quinteros, Carter, et al., 2021; Rudzinski et al, 2021; Péquegnat et al., 2021; Schweitzer et al., 2021; Senturk et al., 2021; Shahvar et al., 2021; Spallarossa et al., 2021; Stammler et al., 2021; Strollo et al., 2021; Veikkolainen et al., 2021).

The development of the new Italian strong-motion database ITACA (ITalian AC-celerometric Archive, http://itaca.mi.ingv.it) is in progress under the sponsorship of the National Department of Civil Protection (DPC) within Project S4, in the framework of DPC-INGV 2007–2009 research agreement. This work started from the alpha version of ITACA [8], where 2,182 3-component records from 1,004 earthquakes, mainly recorded by the National Accelerometric Network, RAN, operated by DPC, were processed and included in the database. Earthquake metadata, recording station information and reports on the available geologicalgeophysical information of 452 recording sites, corresponding to about 70% of the total, were also included. Subsequently, ITACA has been updated and will reach its final stage by the end of Project S4, around mid-2010, with additional features, improved information about recording stations, and updated records, including the Mw6.3 L’Aquila earthquake. All records were re-processed with respect to the alpha version [9], with a special care to preserve information about late-triggered events and to ensure compatibility of corrected records, i.e., velocity and displacement traces obtained by the first and second integral of the corrected acceleration should not be affected by unrealistic trends. After a short introduction of ITACA and its most relevant features and statistics, this paper mainly deals with the newly adopted processing scheme, with reference to the problems encountered and the solutions that have been devised.

Using records from co-located broad-band and digital strong motion instruments, it is first shown that the displacement waveforms obtained by double integration of the accelerogram need not be free of unrealistic baseline drift to yield reliable spectral ordinates up to at least 10 s. Secondly, to provide objective criteria for selecting reliable digital strong motion records for ground motion predictions at long periods, a set of synthetic accelerograms contaminated by random long period noise has been used and the difference between the original accelerograms and the spurious ones in terms of response spectra has been quantified, by introducing a noise index that can be easily calculated based on the velocity waveform of the record. The results of this study suggest that high-pass filtering the digital acceleration record from a cut-off period selected to suppress baseline drifts on the displacement waveform appears to be in most cases too conservative and unduly depletes reliable information on long period spectral ordinates

Several cases of strong motion data recorded in alluvial basins show very high amplification effects that exceed, at medium and long periods, those predicted by empirical relations or included in standard reference codes. Among others, we recall here the earthquakes of San Fernando (1972), Northridge (1994) (BSSA, 1996) and the Umbria-Marche sequence of 1997, during which the shaking recorded in the Gubbio Plain (Pacor et al, 2007) provided strong evidence of the phenomenon: extremely high spectral amplification values (higher than reference codes) for 2 < T < 4 s (see Fig. 4). The main reason why these amplifications (“basin effects”) take place lies in the generation, by diffraction at the edges of the valley, of long period surface waves that travel horizontally in the upper sediments of the valley. While the influence of alluvium filled basins on site response has been the subject of substantial research, the resulting modifications on the response spectra at the basin surface (especially for T > 1 - 2 s) has not been as thoroughly investigated (see e. g. Chávez e Faccioli, 2000) despite its importance in structural design. Significant previous studies tried to estimate basin amplification effects through the analysis of strong-motion data and most of them quantified basin geometry only in terms of sediment depth (Trifunac and Lee, 1978), introducing such term in newly developed attenuation models (Campbell, 1997; Field, 2000; Lee and Anderson, 2000). Other studies tried to relate basin effects also to the relative location of source and site position in the basin (Choi et al., 2005), or to the distance to the basin edge (Joyner, 2000). In the S5 project, specific parametric studies involved two different types of basins (both typical of the Italian Peninsula): “enclosed” basins and “open” basins. Results gave great insight of how basin effects amplify seismic motion in connection with the geometry of the basin, with the fault mechanism and with the different valley-fault configurations. Critical in all analyses is the value of the fundamental 1D vibration period of valley centre, T01D, that acts as the theoretical upper limit to 2D basin amplification effects, as stated in Chàvez-García and Faccioli (2000). Its calculation appears thus crucial in the study of the seismic response of valleys and basins. In addition, a detailed study has been devoted to the identification and classification of alluvium filled basins in Italy, and particularly to the parameters that the previous analyses highlighted as the most critical ones in the modification of response spectra.

This report summarizes the seismicity in Switzerland and surrounding regions in the years 2017 and 2018. In 2017 and 2018, the Swiss Seismological Service detected and located 1227 and 955 earthquakes in the region under considera- tion, respectively. The strongest event in the analysed period was the ML 4.6 Urnerboden earthquake, which occurred in the border region of cantons Uri, Glarus and Schwyz on March 6, 2017. The event was the strongest earthquake within Switzerland since the ML 5.0 Vaz earthquake of 1991. Associated ground motions indicating intensity IV were reported in a radius up to about 50 km and locally approached intensity VI in the region close to the epicentre. Derived focal mechanisms and relative hypocentre relocations of the immediate aftershocks image a NNW–SSE striking sinistral strike-slip fault. Together with other past events in this region, the Urnerboden earthquake suggests the existence of a system of sub-parallel strike-slip faults, likely within in the uppermost crystalline basement of the eastern Aar Massif. A vigorous earthquake sequence occurred close to Château-d’Oex in the Préalpes-Romandes region in western Switzer- land. With a magnitude of ML 4.3, the strongest earthquake of the sequence occurred on July 1, 2017. Focal mechanism and relative relocations of fore- and aftershocks image a NNE dipping normal fault in about 4 km depth. Two similarly oriented shallow normal-fault events occurred between subalpine Molasse and Préalpes units close to Châtel-St-Denis and St. Silvester in 2017/18. Together, these events indicate a domain of NE–SW oriented extensional to transtensional deformation along the Alpine Front between Lake Geneva in the west and the Fribourg Fault in the east. The structural complexity of the Fribourg Fault is revealed by an ML 2.9 earthquake near Tafers in 2018. The event images a NW–SE striking fault segment within the crystalline basement, which might be related to the Fribourg Fault Zone. Finally, the ML 2.8 Grenchen earthquake of 2017 provides a rare example of shallow thrust faulting along the Jura fold-and-thrust belt, indicating contraction in the northwestern Alpine foreland of Switzerland.

In this article we describe EPOS Seismology, the Thematic Core Service consortium for the seismology domain within the European Plate Observing System infrastructure. EPOS Seismology was developed alongside the build-up of EPOS during the last decade, in close collaboration between the existing pan-European seismological initiatives ORFEUS (Observatories and Research Facilities for European Seismology), EMSC (Euro-Mediterranean Seismological Center) and EFEHR (European Facilities for Earthquake Hazard and Risk) and their respective communities. It provides on one hand a governance framework that allows a well-coordinated interaction of the seismological community services with EPOS and its bodies, and on the other hand it strengthens the coordination among the already existing seismological initiatives with regard to data, products and service provisioning and further development. Within the EPOS Delivery Framework, ORFEUS, EMSC and EFEHR provide a wide range of services that allow open access to a vast amount of seismological data and products, following and implementing the FAIR principles and supporting open science. Services include access to raw seismic waveforms of thousands of stations together with relevant station and data quality information, parametric earthquake information of recent and historical earthquakes together with advanced event-specific products like moment tensors or source models and further ancillary services, and comprehensive seismic hazard and risk information, covering latest European scale models and their underlying data. The services continue to be available on the well-established domain-specific platforms and websites, and are also consecutively integrated with the interoperable central EPOS data infrastructure. EPOS Seismology and its participating organizations provide a consistent framework for the future development of these services and their operation as EPOS services, closely coordinated also with other international seismological initiatives, and is well set to represent the European seismological research infrastructures and their stakeholders within EPOS.

The behaviour of the ground surface and of structures subjected to earthquakes can be estimated analysing the accelerograms of seismic records. The ground motion is strongly dependent on several factors and the ability to record, characterize and extract the main features of waveforms is essential to better understand these dependencies. One of the most difficult steps of this analysis is the waveforms’ processing. Its purpose is the estimation and the removal of noise in the records, to evaluate reliable ground motion. In this framework a processing tool fully integrated within the Engineering Strong Motion (ESM) database was designed [Paolucci et al., 2011; Luzi et al., 2016]. In the last decade the number of waveforms is sharply increased and so is the time it takes to process them. To solve this issue a possible solution is to broaden the number of qualified people involved in the processing. The main aim of this tutorial is to teach the largest number of people how to use the ESM processing tool and to provide some important guidelines for the thresholds of the parameters to set. In the text a step by step processing routine is depicted with a description of the purpose for each parameter. In addition, a suite of explanatory examples with peculiar situations is given.

Strong ground motion records and free open access to strong‐motion data repositories are fundamental inputs to seismology, engineering seismology, soil dynamics, and earthquake engineering science and practice. This article presents the current status and outlook of the Observatories and Research Facilities for European Seismology (ORFEUS) coordinated strong‐motion seismology services, namely the rapid raw strong‐motion (RRSM) and the engineering strong‐motion (ESM) databases and associated web interfaces and webservices. We compare and discuss the role and use of these two systems using the Mw 6.5 Norcia (Central Italy) earthquake that occurred on 30 October 2016 as an example of a well‐recorded earthquake that triggered major interest in the seismological and earthquake engineering communities. The RRSM is a fully automated system for rapid dissemination of earthquake shaking information, whereas the ESM provides quality‐checked, manually processed waveforms and reviewed earthquake information. The RRSM uses only data from the European Integrated Waveform Data Archive, whereas the ESM also includes offline data from other sources, such as the ITalian ACcelerometric Archive (ITACA). Advanced software tools are also included in the ESM to allow users to process strong‐motion data and to select ground‐motion waveform sets for seismic structural analyses. The RRSM and ESM are complementary services designed for a variety of possible stakeholders, ranging from scientists to the educated general public. The RRSM and ESM are developed, organized, and reviewed by selected members of the seismological community in Europe, including strong‐motion data providers and expert users. Global access and usage of the data is encouraged. The ESM is presently the reference database for harmonized seismic hazard and risk studies in Europe. ORFEUS strong‐motion data are open, “Findable, Accessible, Interoperable, and Reusable,” and accompanied by licensing information. The users are encouraged to properly cite the data providers, using the digital object identifiers of the seismic networks.