SM2.3

ORFEUS (Observatories and Research Facilities for European Seismology; http://orfeus-eu.org/) is a non-profit foundation that promotes observational seismology in the Euro-Mediterranean area through the collection, archival and distribution of seismic waveform data, metadata, and closely related services and products. The data and services are collected or developed at national level by more than 60 contributing Institutions in Pan-Europe and further enhanced, integrated, standardized, homogenized and promoted through ORFEUS. Among the goals of ORFEUS are: (a) the development and coordination of waveform data products; (b) the coordination of a European data distribution system, and the support for seismic networks in archiving and exchanging digital seismic waveform data; (c) the encouragement of the adoption of best practices for seismic network operation, data quality control and FAIR data management; (d) the promotion of open access to seismic waveform data, products and services for the broader Earth science community. These goals are achieved through the development and maintenance of services targeted to a broad community of seismological data users, ranging from earth scientists to earthquake engineering practitioners. Two Service Management Committees (SMCs) are consolidated within ORFEUS devoted to managing, operating and developing (with the support of one or more Infrastructure Development Groups): (i) the European Integrated Data Archive (EIDA; https://www.orfeus-eu.org/data/eida/); and (ii) the European Strong-Motion databases (SM; https://www.orfeus-eu.org/data/strong/). New emerging groups within ORFEUS are focused on mobile pools and computational seismology. ORFEUS services currently provide access to the waveforms acquired by ~ 14,500 stations, including dense temporary experiments, with strong emphasis on open, high-quality data. Contributing to ORFEUS data archives means benefitting from long-term archival, state-of-the-art quality control, improved access, increased usage, and community participation. Access to data and products is ensured through state-of-the-art information and communication technologies, with strong emphasis on federated web services that considerably improve seamless user access to data gathered and/or distributed by the various ORFEUS institutions. Web services also facilitate the automation of downstream products. Particular attention is paid to adopting clear policies and licenses, and acknowledging the crucial role played by data providers / owners, who are part of the ORFEUS community. There are significant efforts by ORFEUS participating Institutions to enhance the existing services to tackle the challenges posed by the Big Data Era, with emphasis on data quality, improved user experience, and implementation of strategies for scalability, high-volume data access and archival. ORFEUS data and services are assessed and improved through the technical and scientific feedback of a User Advisory Group (UAG), which comprises European Earth scientists with expertise on a broad range of disciplines. All ORFEUS services are developed in coordination with EPOS and are largely integrated in the EPOS Data Access Portal, as ORFEUS is one of the founding Parties and fundamental contributors of the EPOS Thematic Core Service for Seismology (https://www.epos-eu.org/tcs/seismology). In this contribution, we selectively present the activities of ORFEUS, with the main aims of facilitating seismological data discovery and encouraging open data sharing and integration, as well as promoting best practice in observational seismology.

How to cite: Cauzzi, C., Bieńkowski, J., Custódio, S., D'Amico, S., Evangelidis, C., Guéguen, P., Haberland, C., Haslinger, F., Lanzano, G., Ottemöller, L., Rondenay, S., Sleeman, R., and Strollo, A.: ORFEUS Services and Activities to Promote Observational Seismology in Europe and beyond, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6119, https://doi.org/10.5194/egusphere-egu21-6119, 2021.

With the setup of EIDA (the European Integrated Data Archive https://www.orfeus-eu.org/data/eida/) in the framework of ORFEUS, and the implementation of FDSN-standardized web services, seismic waveform data and instrumentation metadata of most seismic networks and data centers in Europe became accessible in a homogeneous way. EIDA has augmented this with the WFcatalog service for waveform quality metadata, and a routing service to find out which data center offers data of which network, region, and type. However, while a distributed data archive has clear advantages for maintenance and quality control of the holdings, it complicates the life of researchers who wish to collect data archived across different data centers. To tackle this, EIDA has implemented the “federator” as a one-stop transparent gateway service to access the entire data holdings of EIDA.

To its users the federator acts just like a standard FDSN dataselect, station, or EIDA WFcatalog service, except for the fact that it can (due to a fully qualified internal routing cache) directly answer data requests on virtual networks.

Technically, the federator fulfills a user request by decomposing it into single stream epoch requests targeted at a single data center, collecting them, and re-assemble them to a single result.

This implementation has several technical advantages:

• It avoids response size limitations of EIDA member services, reducing limitations to those imposed by assembling cache space of the federator instance itself.
• It allows easy merging of partial responses using request sorting and concatenation, and reducing needs to interpret them. This reduces computational needs of the federator and allows high throughput of parallel user requests.
• It reduces the variability of requests to end member services. Thus, the federator can implement a reverse loopback cache and protect end node services from delivering redundant information and reducing their load.
• As partial results are quick, and delivered in small subunits, they can be streamed to the user more or less continuously, avoiding both service timeouts and throughput bottlenecks.

The advantage of having a one-stop data access for entire EIDA still comes with some limitations and shortcomings. Having requests which ultimately map to a single data center performed by the federator can be slower by that data center directly. FDSN-defined standard error codes sent by end member services have limited utility as they refer to a part of the request only. Finally, the federator currently does not provide access to restricted data.

Nevertheless, we believe that the one-stop data access compensates these shortcomings in many use cases.

Further documentation of the service is available with ORFEUS at http://www.orfeus-eu.org/data/eida/nodes/FEDERATOR/

How to cite: Kaestli, P., Armbruster, D., and EIDA Technical Committee, T.: The EIDA federator – a one-stop access to EIDA seismic data holdings, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15558, https://doi.org/10.5194/egusphere-egu21-15558, 2021.

Recently a set of quality control procedures have been implemented at the data center of the BGR (Seismic Survey of Germany). Goal is to identify unusual deviations in amplitude, timing and waveform caused by data and metadata errors. One of the strategies applied is to evaluate long term observations of seismic noise at specific frequencies at many stations. Particularly at lower frequencies this analysis is quite sensitive to amplitude changes. Also useful is the characterization of station sites by looking at anthropogenic noise patterns in a frequency range of 4-14 Hz. The sites show fundamental differences when looking at daily and weekly noise patterns and some also have specific responses to local wind. Changes in the noise patterns indicate changes in the environment or uncompensated hardware or metadata changes. Furthermore, correlations of teleseismic signals reveal  possible inconsistencies in waveform shape, travel time residuals and amplitudes within the station set. When applied systematically a statistical  analysis of the correlation parameters indicates long term deviations in these three observables. Finally, a formal check of the transfer function given in the metadata is implemented to identify wrong settings in the normalization and illegal specifications in the poles and zeros (conjugate complex pairs and negative real part at poles). These implemented measures help us to keep our data at a high quality level and to react quickly on the occurrence of  hardware and metadata errors.

How to cite: Stammler, K.: Waveform quality checks at German networks, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5889, https://doi.org/10.5194/egusphere-egu21-5889, 2021.

Résif, the French seismological and geodetic network, was launched in 2009 in an effort to develop, modernize, and centralize geophysical observation of the Earth’s interior. This French research infrastructure uses both permanent and mobile instrument networks for continuous seismological, geodetic and gravimetric measurements.

Résif-SI is the Information System that manages, validates and distributes seismological data from Résif.

The construction of Résif-SI has lead to a federated organisation gathering several data and metadata producers (Nodes) and a national Seismological Data Centre.

The Résif Seismological Data Centre is one of 19 global centres distributing data and metadata in formats and using protocols which comply with International Federation of Digital Seismograph Networks (FDSN) standards. It is also one of the eleven nodes in EIDA, the European virtual data centre and seismic data portal in the European Plate Observing System (EPOS) framework.

Inside Résif-SI, each Node has it's specificities and dedicated procedures in order to manage and validate the data and metadata workflow from the station instruments to the Résif Seismological Data Centre.

To meet the expectations and needs of the end user in terms of data quality, metadata consistency and service availability, Résif-SI operates a complex set of quality enhancement operations.

This contribution will present the quality expectations that are in the core of Résif-SI, and show the methods and tools that help us meeting the expectations, and that could be of interest for the rest of the community.

We will then list some of our quality improvement projets and the expected results.

How to cite: Schaeffer, J., Engels, F., Grunberg, M., Maron, C., Pardo, C., Saurel, J.-M., Wolyniec, D., Arnoul, P., Bollard, P., Touvier, J., Chèze, J., Peix, F., and Pequegnat, C.: Improving data, metadata and service quality within Résif-SI, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12436, https://doi.org/10.5194/egusphere-egu21-12436, 2021.

The Maltese islands are a small country 15 km wide by 30 km long located about 100 km south of Sicily, Italy. Since 2015 Malta has set up a national seismic network. The primary aim of this network is to monitor in real-time and to locate more accurately the seismicity close to the islands and the seismicity in the Sicily Channel, offshore between Sicily, Tunisia and Libya. This Channel presents a range of interesting and complex tectonic processes that have developed in response to various regional stress fields mainly as a result of the collision between the African plate with Europe. The Maltese islands are known to have been affected by a number of earthquakes originating in the Channel, with some of these events estimated to be very close to the islands.

The seismotectonic characteristics of the Sicily channel, particularly south of the Maltese islands, is not well understood. This situation is being partially addressed through an increase in the number of seismic stations on the Maltese archipelago. The Malta Seismic Network (FDSN code ML), managed by the Seismic Monitoring and Research Group, within the Department of Geosciences, University of Malta, currently comprises 8 broadband, 3-component stations over an area slightly exceeding 300 km². We present a technical description of the MSN including quality control tests such as spectral analysis (Power Spectral Density and HVSR), station orientations and timings as well as examples of local and regional earthquakes recorded on the network. We describe the upgrades to real-time data transmission and archiving, and automated epicentre location for continuous seismic monitoring using the local network amalgamated with a virtual seismic network to monitor the seismicity in the extended Mediterranean region. Such a dense national network, besides improving epicentral location in the Sicily Channel, is providing valuable information on microearthquake activity known to occur in close proximity to the islands, which has been very difficult to study in the past. It also provides an important tool for analysing site response and site amplification related to underlying geology, which constitutes a major component of seismic hazard analysis on the islands. Furthermore, the increase in seismic stations to the seismic monitoring system provides more robust earthquake estimates for the tsunami monitoring/simulation system.

Funding for stations was provided by Interreg Italia-Malta projects (SIMIT and SIMIT-THARSY, Codes B1-2.19/11 and C1-3.2-57) and by Transport Malta.

How to cite: Galea, P., Agius, M., Bozionelos, G., D'Amico, S., and Farrugia, D.: The national seismic network for the Maltese islands: Update 2021, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8510, https://doi.org/10.5194/egusphere-egu21-8510, 2021.

The rapid increase of seismic waveforms, due to the increment of seismic stations and continuous real-time streaming to data centres, leads to the need for automatic procedures aimed at supporting data processing and data quality control. In this study, we propose a semi-automatic procedure for the consistency check of large strong-motion datasets, classifying the anomalies observed on the residuals analysis and identifying the possible causes.

The data collected in the strong-motion databases are usually arranged as parametric tables (called flatfiles), used to disseminate the Intensity Measures (IMs) and the associated metadata of the processed waveforms. This is the current practice for the ITalian ACcelerometric Archive (ITACA, D’Amico et al., 2020) and Engineering Strong Motion (ESM; Lanzano et al. 2019a) databases. The adopted criteria for flatfile compilation are designed to collect IMs and related metadata in a uniform, updated, and traceable way, with the aim of providing datasets useful to develop Ground Motion Models (GMMs) for Probabilistic Seismic Hazard Assessment (PSHA) and engineering applications. Therefore, the consistency check of the flatfiles is a crucial task to improve the quality of the products provided by the waveform services.

The proposed procedure is based on the residual distributions obtained from ad-hoc ground motion prediction equations for the ordinates of the 5% damped acceleration response spectra. In this study, we focus on the active shallow crust events in ITACA, considering the ITA18 ground motion model (Lanzano et al., 2019b) as a reference for Italy. The total residuals, computed as logarithm difference between observations and predictions, are decomposed in between-event, between-station and event-and-station corrected residuals by applying a mixed-effect regression (Bates et al., 2015). This is the common practice for the (partial) removal of the ergodic assumption in empirical GMMs (e.g., Stafford 2014), where the contribution of the systematic corrective effects of event and station on aleatory variability are identified and shifted to the epistemic uncertainty. Afterward, the proposed procedure is applied to raise a warning in case of anomalous residual values. Warnings are provided when the normalized residuals exceed a certain threshold, in three ranges of periods (i.e., 0.01-0.15 s, 0.15-1 s, 1-5 s). The causes of warnings may be several and may concern the event, the site, the waveform, or a combination of them. Among the possible sources of anomalous trends, the more common are: preliminary or inaccurate event localization or magnitude, wrong soil category assigned based on proxies, misleading tectonic regime assigned to the earthquake, and fault directivity that may cause strong-ground motion amplification in certain directions. Warnings may also raise for peculiarities in the site-response (e.g., large amplifications/de-amplifications at certain frequency-bands) and to the occurrence of near-source effects in the waveforms (see Pacor et al., 2018). Based on the raised warnings, a decision tree classifier is developed to identify the common anomaly sources and to support the consistency check of the semi-automatic procedure.

This study may help to enhance the waveform services and related products, besides reducing the variability of ground motion models and guiding decisions for site characterization studies and network maintenance.

How to cite: Mascandola, C., Lanzano, G., and Pacor, F.: Residual analysis of large strong-motion flatfiles as a tool for detecting data error and anomalies, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6195, https://doi.org/10.5194/egusphere-egu21-6195, 2021.

Three-component seismograms recorded by seismic sensors are momentous data to study the source mechanism of earthquakes. Correct orientation of sensors relative to the true north is important for the waveform inversion techniques. Yet, the non-precise orientation of horizontal components of seismic sensors has been reported in many seismic networks worldwide. In this study, we evaluated the effect of sensor misorientations (deviations from the true north) on time-domain moment tensor inversion, relying on the recent sensor orientation studies on broadband seismic networks in Iran and Turkey. We selected several well-recorded countrywide local and regional moderate magnitude earthquakes, which are associated with the tectonic events, in the time period of 2012-2019. We calculated the moment tensor inversion of those events before and after applying the orientation correction using a Bayesian bootstrap-based probabilistic method. This leads to reaching the uncertainties and trade-offs of parameters and helps to stabilize the inversion. Our analysis shows that in the presence of misoriented sensors, an approximate solution is achievable. However, this includes the remarkable uncertainties in inverted parameters and makes the reliable determination of the moment tensor’s elements challenging. We also found an additional significant non-double couple component while using the misoriented radial and transverse components. Results show that the misfit and uncertainties decrease significantly when sensor orientation correction applied. We suggest that the evaluation of metadata should be part of data processing in seismic networks and data centers, to report more reliable moment tensor solutions.

How to cite: Jamalreyhani, M., Rezapour, M., and Büyükakpınar, P.: Evaluation of seismic sensor orientations in the full moment tensor inversion results, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-459, https://doi.org/10.5194/egusphere-egu21-459, 2021.

Accurate timing of seismic records is essential for almost all applications in seismology. Wrong timing of the waveforms may result in incorrect Earth models and/or inaccurate earthquake locations. As such, it may render interpretations of underground processes incorrect. Ocean bottom seismometers (OBSs) experience clock drifts due to their inability to synchronize with a GNSS signal (with the correct reference time), since electromagnetic signals are unable to propagate efficiently in water. As OBSs generally operate in relatively stable ambient temperature, the timing deviation is usually assumed to be linear. Therefore, the time corrections can be estimated through GPS synchronization before deployment and after recovery of the instrument. However, if the instrument has run out of power prior to recovery (i.e., due to the battery being dead at the time of recovery), the timing error at the end of the deployment cannot be determined. In addition, the drift may not be linear, e.g., due to rapid temperature drop while the OBS sinks to the seabed. Here we present an algorithm that recovers the linear clock drift, as well as a potential timing error at the onset.

The algorithm presented in this study exploits seismic interferometry (SI). Specifically, time-lapse (averaged) cross-correlations of ambient seismic noise are computed. As such, virtual-source responses, which are generally dominated by the recorded surface waves, are retrieved. These interferometric responses generate two virtual sources: a causal wave (arriving at a positive time) and an acausal wave (arriving at a negative time). Under favorable conditions, both interferometric responses approach the surface-wave part of the medium's Green's function. Therefore, it is possible to calculate the clock drift for each station by exploiting the time-symmetry between the causal and acausal waves. For this purpose, the clock drift is calculated by measuring the differential arrival times of the causal and acausal waves for a large number of receiver-receiver pairs and computing the drift by carrying-out a least-squares inversion. The methodology described is applied to time-lapse cross-correlations of ambient seismic noise recorded on and around the Reykjanes peninsula, SW Iceland. The stations used for the analysis were deployed in the context of IMAGE (Integrated Methods for Advanced Geothermal Exploration) and consisted of 30 on-land stations and 24 ocean bottom seismometers (OBSs).  The seismic activity was recorded from spring 2014 until August 2015 on an area of around 100 km in diameter (from the tip of the Reykjanes peninsula).

How to cite: Naranjo, D., Parisi, L., Jousset, P., Weemstra, C., and Jónsson, S.: Determining OBS clock drift using ambient seismic noise, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13999, https://doi.org/10.5194/egusphere-egu21-13999, 2021.

The Lower Rhine Embayment in western Germany is one of the most important areas of earthquake recurrence north of the Alps, facing a moderate level of seismic hazard in the European context but a significant level of risk due to a large number of important industrial infrastructures. In this context, the project ROBUST aims at designing a user-oriented hybrid earthquake early warning and rapid response system where regional seismic monitoring is combined with smart, on-site sensors, resulting in the implementation of decentralized early warning procedures.

One of the research areas of this project deals with finding an optimal regional seismic network arrangement. With the optimally compacted network, strong ground movements can be detected quickly and reliably. In this work simulated scenario earthquakes in the area are used with an optimization approach in order to densify the existing sparse network through the installation of additional decentralized measuring stations. Genetic algorithms are used to design efficient EEW networks, computing optimal station locations and trigger thresholds in recorded ground acceleration. By minimizing the cost function, a comparison of the best earthquake early warning system designs is performed and the potential usefulness of existing stations in the region is considered as will be presented in the meeting.

How to cite: Najdahmadi, B., Pilz, M., Bindi, D., Njara Tendrisoa Razafindrakoto, H., Oth, A., and Cotton, F.: Robust, an Earthquake Early Warning System in the Lower Rhine Embayment, Germany, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7997, https://doi.org/10.5194/egusphere-egu21-7997, 2021.

A more capable infrastructure would enable greater monitoring capabilities. We propose a deeper grouted casing and using borehole best practices to ensure improved coupling and a better environment for reducing site and emplacement noise in both high and low frequencies and specifically the horizontal component recording. Casing emplacements should be a one to two day operation for installation. Stations using the new Trillium T120PH Slim or dual sensor Cascadia Slim in a single cased hole will have wider bandwidth, larger dynamic range, resiliency and low noise recording that would enable new observations along with higher sensitivity for local earthquake recording. Dry cased holes are the standard for long term geophysical observatories and a better investment when all the associated costs of operating observatories are considered. Facilities are both renewing old stations and trying to improve array performance through these new instruments.  This line of Trillium borehole instruments are very robust with low SWaP (Size, Weight and Power), a 300 meter continuous immersion rating and of corrosion resistant construction.  These sensors can be installed in bedding material or with a hole lock and are compatible with the ultimate installation, grouting it in!

How to cite: Parker, T., Hamilton, V., and Moores, A.: A More Capable Array Infrastructure, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13884, https://doi.org/10.5194/egusphere-egu21-13884, 2021.