AlpArray is a large collaborative seismological project in Europe that includes more than 50 research institutes and seismological observatories. At the heart of the project is the collection of top-quality seismological data from a dense network of broadband temporary seismic stations, in compliment to the existing permanent networks, that ensures a homogeneous station coverage of the greater Alpine region. This Alp Array Seismic Network (AASN) began operation in January 2016 and will have a duration of at least 2 years. In this work we report the Swiss contribution to the AASN, we concentrate on the site selection process, our methods for stations installation, data quality and data management. We deployed 27 temporary broadband stations equipped with STS-2 and Trillium Compact 120 s sensors.
The deployment and maintenance of the temporary stations across 5 countries is managed by ETH Zurich and it is the result of a fruitful collaboration between five institutes in Europe.
In order to gain a deep understanding of the solid Earth system, including
fields as diverse as seismotectonics, lithosphere structure, geodynamics and
earthquake hazard, high-quality seismic data from dense networks are a
pre-requisite. It is increasingly common to deploy large-scale temporary
seismic experiments that complement existing permanent seismic stations and
improve the spatial resolution of scientific studies. Recent and well-known
examples of major scientific projects that target improved resolution using
temporary seismic networks are the USArray (
While selecting sites for permanent broadband stations usually includes a long, careful and expensive site search, noise tests and vault construction, in a temporary deployment one has to find a good compromise between time, budget, feasibility and project requirements in terms of network geometry and data quality.
In this work we describe the Swiss contribution in the AlpArray Seismic Network in terms of the existing permanent stations, site selections and installations of temporary stations, data quality and data management. The deployment and maintenance of the 27 Swiss temporary broadband stations is led by ETH Zurich (Seismology and Geodynamics group, SEG, and the Swiss Seismological Service, SED). These stations are a product of a fruitful collaboration between five institutes in Europe, supported by funding from the Swiss-AlpArray SINERGIA program of the Swiss National Science Foundation.
AlpArray (
The AlpArray science plan relies on the collection of high-quality
seismological data from a dense network of broadband temporary seismic
stations, that, in addition to the permanent broadband networks, ensures
homogeneous coverage of the Alpine area, with station spacing of
Map of the AlpArray broadband seismic stations, with the permanent stations (red inverted triangles), the new permanent French stations (grey inverted triangles) for which the installation is expected during the AlpArray project, the AlpArray temporary stations (white circles) and the Ocean Bottom Seismometer plan (grey circles). The Swiss installations are marked with red circles, labelled with the station name. The grey line marks the AlpArray boundary. MONC, SARZ and PRMA are three permanent INGV stations discussed in Fig. 6.
It is important to mention the main deployment rules that constrain the site selection for the temporary broadband station. To ensure a proper spatial coverage, every AlpArray temporary station should be within a 3 km radius from the initially proposed locations. Deviations up to a 6 km radius are allowed for specific reasons and only after approval of the AlpArray Seismic Network managers. No strict technical specification is given for the installation and vault setup. Rather, mandatory guidelines concerning the site-noise level must be satisfied. The allowed site-noise levels for all 3 components are defined using PSDs typically computed using PQLX (McNamara and Boaz, 2005). The median value for the noise should be 20dB lower than the New High Noise Model (NHNM) (Peterson, 1993) from 20 Hz up to 100 s, excluding the microseismic peak (5–20 s) The only exception is made for the long period (20–100 s) horizontal components for which the noise level can be up to 10 dB lower then NHNM, to account for noise associated with temperature and pressure fluctuations that introduce ground tilt, which is difficult to avoid in temporary deployments. There are additional requirements placed on the deployed hardware. Each seismic sensor must have 3 components and be broadband with a flat velocity-response in the frequency domain from at least 0.03 to 20 Hz, preferably down to 0.008 Hz. Digitisers must be > 130 dB between 0.1 and 10 Hz and all data must be recorded with 100 sps or higher sampling rate. The data have to be provided to an EIDA node in miniSEED format preferably in near-real time, but in the absence of real-time communications data should be retrieved with a latency of maximum 3 months. Real-time data streaming or station health information is highly recommended to ensure a timely checking of the station performance. In the long term, this has a better cost/result ratio than an off-line site. All AASN station operators should be capable of providing correct dataless SEED information.
Here we describe our temporary station concept and site selection scheme used for the Swiss station deployed that allow us to reach the AASN quality criteria and to provide high quality seismic data to the AlpArray project.
Components of an ETH temporary station.
The Swiss-AlpArray SINERGIA project covers the cost for deployment and
operation for 2 to 3 years of
The large scale morphology and geology of the 27 sites are diverse: 8 are located within or on the hilly border of the Po Plain basin; 4 are within or in the hilly part of the Pannonian basin, 2 are in the Sava and Kupa valleys, and 13 are on mountainous terrain (Swiss Alps, Dolomites, and Dinarides). While there are many parts of the AlpArray area that can be considered challenging regions for finding low-noise sites for seismic stations, the large and deep sedimentary basins of the Po Plain, Molasse and Pannonian basin are some of the most challenging targets for the AASN due to high population and infrastructure density. In the Dinarides, an unusual constraint on site selection was personal safety, in particular avoiding minefields.
A Swiss temporary seismic station in AASN consists of the following
components (Fig. 2): STS-2 (120 s) or Trillium Compact 120 s sensor
(Fig. 2a, b), Taurus 3-channel 24 bit digitizer (Fig. 2c) with > 141 dB
dynamic range (100 sps sampling rate), GPS antenna,
AnyRover mobile access router (Dual-Modem High-speed LTE and WLAN Router)
for real-time data communication, mobile antenna 4G-LTE (Fig. 2d) and 65Ah
battery (Fig. 2e). In those sites where mains power supply is not
available, the station is powered by 2 solar panels with 30 W peak power,
17.6 V voltage and 1.68 A current each (Fig. 2f). All stations always
support real-time data stream, expect at the handful of sites powered by
solar,, where in order to save energy, the data is transferred daily only in
a single 2 h window (quasi-real time communication). The router can be
remotely controlled, rebooted, turned on and off via SMS (Short Message
Service). In addition to the real-time streaming to SED-ETH servers in
Zurich, the data is also stored locally on a 16 or 24 GB flash cards.
With our configuration, a real-time streaming station power rating is
We use a water-proof “PeliCase” with all the necessary connectors to protect and to thermally isolate the digitizer and the router (Fig. 2c, h). Thermal isolation for the sensor (especially important for the STS-2) is ensured, for in-house installations (23 sites), by a 5 cm thick box made of polystyrene and wood that is also used for STS-2 transportation (Fig. 2g), on top of a polystyrene frame. In many sites, we cover this box with a rescue blanket (see Fig. 3h) to provide further protection from direct sunlight. The sensor is usually placed on cement, in the ground floor of small houses. In presence of tiles, we preferably remove them or we make sure they are well connected with the cement-floor base.
4 sensor are deployed in buried hand-dug vaults. Our prototype vault consists of a buried, waterproof, bottomless barrel inserted into an up to 20 cm of cement plate. In one case, we had to build a drainage channel to avoid standing water around and inside the barrel. In these cases, the station hardware is identical to other sites and the sensor is thermally isolated with mineral wool and flexible polystyrene panels. For the AlpArray project, we deployed 24 STS-2 and 3 Trillium Compact 120 s.
When selecting the optimal site for a seismic station, there is always a
compromise between the available budget and manpower, local and regional
geology and land use, and available hardware. There are well-established
general field procedures and rules for site search (e.g.
For the AlpArray project we based our site scouting on the following general principles:
Network geometry: We follow the agreed 3 resp. 6 km rule described above. We were forced to go beyond the 3 km radius on a few occasions where the initial targeted position was in the middle of inaccessible mountains (A288A, with no possibility to reach the station during winter time) or in the middle of a large city (A285A, Fiorenzuola D'Arda, Italy, where the high-speed train line and a highway are close-by throughout the 3 km radius) and in some sites in Bosnia and Herzegovina as well as Croatia where terrain morphology or accessibility did not allow safe site access.
Off-site studies: Much of the site scouting can be accomplished from the office. From a first web search including google maps a set of plausible sites are selected, then possible owners and local and regional authorities are contacted. Communicating with local authorities about seismic site requirements is a very important step: their deep knowledge of the area, especially concerning land ownership, allows quick rejection of many potential sites, and to rapid permissioning for installation. Even in advance of a site visit, it is possible to have an idea of the suitability of the site in terms of accessibility, safety, and resources – power, communications, sky visibility for GPS. However, a site visit for inspection before the final installation is mandatory. We always check the geological condition of the potentials sites, preferring rocky sites with low slope. All this work minimizes upcoming fieldwork efforts and their associated costs.
Permission, accessibility and safety: Normally, sites should be accessible by car (or within half an hour walking distance) year-round, in all reasonable weather conditions. The instruments should not be exposed to risk of flood, vandalism and other potential damage. For safety, we prefer indoor sites that can be locked or sites not easily accessible by the general public.
Seismic noise evaluation: We search for sites that are as distant as possible from any human activity, such as towns, industry, constructions, transportation, pipelines, electrical lines, mines, agriculture, rivers, tidal areas, trees, etc. Nowadays, especially in the Po Plain and in the Pannonian basin, but also in very busy mountain valleys (Dolomites) it can be practically impossible to find surface sites far from anthropogenic noise sources. If a building is seing selected, it cannot be actively used by people or animals, or have active heating systems, water pumps, or any other kind of noisy devices. We generally seek to maintain a minimum of 3–4 km distance from railroads, 2–3 km from major highways, and 100–500 m from small local roads. Avoiding these kinds of noise sources significantly improves the likelihood of meeting the high-frequency noise requirements. For the broadband sensors used in AlpArray, long-period performance is susceptible to noise arising from temperature and pressure instabilities, a poorly levelled sensor, and horizontal tilt of the sensor mainly due to vehicular traffic, trains and people that affect the building (or vault) in which the sensor is installed. To reach the low-frequency noise requirements (median PSD noise level at or below 20 dB less than the NHNM for the vertical component and 10 dB less for the horizontal) we consider sites in small, one-story buildings with cement floor and far away from possible persistent traffic of people (50 m) and cars (1–2 km). Small, stiff buildings are preferred to larger ones because their natural frequencies do not interfere with the frequency range of interest (0.009–10 Hz) for most scientific purposes. It is well known that an appropriate thermal insulation of the sensor strongly improves the noise level at long periods on all components (e.g. Langlais et al., 2013), and sensors are always insulated (Fig. 2). Pre-installation noise tests at plausible sites can strongly help in assessing the quality of a site and in avoiding unpleasant surprises. At certain sites, when the agreed noise level was exceeded, the station was moved to a quieter site (an example is the A283A station, see Sect. 3.4).
Connectivity and data transmission: one of our main goals is to have real-time data transmission, so that the stations can be used for alerting purposes, but also for station health verification. Knowing whether a station is working can prevent unnecessary site visits, and optimise station up-time as problems are immediately recognised. Our router device supports the use of standard mobile SIM-cards with data traffic, hence our candidate sites should have a good and stable mobile network coverage. The minimum requirement is a sufficient signal strength and stability to transmit state-of-health data, though preferably continuous 100 sps waveform streams should be transmitted as well. This condition has forced us to discard some potentially good sites, especially in remote mountainous areas.
The GPS signal should be checked and the antenna has to be able to regularly lock onto at least 3–4 satellites to guarantee correct timing and coordinates.
Power supply: In principle our autonomous offline station setup can stay powered, even throughout the Alpine winter, with 2 (30 W) solar panels. Nevertheless, the real-time communication requirement forces us to prefer sites with regular 50 Hz/230 V power grid. For sites with no mains power, we apply a hybrid solution with quasi-real time communication (see Sect. 3.2). A promising site without mains power (i.e., where solar panels are needed) is thus a feasible solution.
Examples of site location and installation configurations
for four housing types (rows). In the first column we show the station
position on Google Earth (red triangles) and, in the second column, pictures
from each installation. One of these picture shows an overview of the site
and a red arrow approximately indicates the sensor locations. The stations
are:
Our final site selection normally falls on those sites that have optimal balance between all the above requirements and principles. Typically, our preferred site is in a small, one-story, uninhabited building with mains power and GSM coverage. Noise tests are performed in most of the sites. However, in some cases, we directly install the stations in the potentially best site (after different site inspections), with the possibility to move the station if the performance is not satisfactory.
The installation of our 27 stations began in September 2015 in Switzerland and in Italy, followed by Bosnia and Herzegovina, Croatia and Hungary. By the official start-date of the project on 1 January 2016, 21 of our stations were operational. The last 3 stations were installed in Croatia in early June 2016. An overview of their basic characteristics are listed in Table 1. Our typical installation in a building takes 3–4 h, while a free-field installation needs 2 days of work by two experienced persons.
Overall, our installations comprise 4 vaults sites and 23 stations installed in small buildings or houses. Only 3 stations are powered by solar panels with data transmission in quasi-real-time,, the rest have mains power and transmit the data in real time to the ETH EIDA node (see Sect. 4.1). According to the internal sensor housing descriptions as defined by SED and used for the AlpArray project, we have four sensor housing types in our temporary station set: tunnel (1), free-field (4), urban free-field (8) and building (14).
The only station installed in a tunnel is station A061A (Fig. 3a).
A tunnel is defined by the SED as man-made subterranean gallery
typically with cylindrical shape with diameter between 1–10 m allowing human
passage. The sensor is placed on a cement base 60
List of the Swiss-AlpArray installed between September
2015 and June 2016, with station name, coordinates, start and end time, type
of housing, sensor (TC
In a free-field station the sensor is defined to be located less than 5 m below surface and farther than one times the height of the surrounding structures. One example is the station A050A in Klekovača, Bosnia and Herzegovina (Fig. 3c) on a bare hill in the middle of a forest. We built two vaults, one for the sensor with a plastic pot with a 20 cm high cement base, and one to host the digitizer, cables and the battery (Fig. 3d). No standing water is expected in that area and the site has slight slope to avoid any possible flooding. The site is inside a meteorological observation station that is fenced and secured.
When sensors are located less than 5 m below surface and within one times the height of the surrounding structures but inside a small 1-story building, we define the housing type as urban free-field. The station A287A in Gattinara (Italy) is an example (Fig. 3e). The sensor is in the ground floor of a largely buried one-story concrete structure with a flat roof rarely used for parking cars. The building is isolated on the hilltop near an old church and tower. The surrounding area is densely covered with vineyards. The sensor is on an exposed hill edge with steep slope below and placed directly on concrete (Fig. 3f). There is mains power and a very good mobile GPRS signal.
If sensors are located inside the basement of a more than one-story building, the housing type is labelled building. Most of our installations are inside remote small buildings where power and mobile coverage were available. The station in Tricerro (Italy) in the Po Plain is an example. The area is intensely cultivated with rice (dense network of water channels and water pumps) and the typical surface terrain is mostly clay and loose sediment. Our first attempt has been the installation of station A283A. The noise level was too high so the station was moved to a new location 1 km away in March 2016. The new station is A283B (Fig. 3g, h) for which the noise levels are more appropriate. The sensor is in a large two-story building, placed directly on concrete. In the whole Po Plain buried cellars are rare because of flood problems. Here we installed solar panels and we protected all the cables from rats (Fig. 3h).
All the sensors are thermally insulated and all the installations are secured following the best practises for installations of (permanent) broadband sensors, STS-2 in particular (e.g. Hutt and Ringler, 2009). The sensor orientation is carefully determined using a compass. However, we are aware of possible errors due to unexpected local disturbance of the magnetic field, especially in buildings and urban areas in general. We plan, in the near future, to verify sensor orientation using teleseismic events (Ekström and Busby, 2008) and to perform careful final orientation of the sensors with a gyrocompass.
The performances in terms of noise levels of the above mentioned example
stations are described in the next section. A complete list of all the
AlpArray temporary installations can be found in the ORFEUS Station Book
(
Median curves of the power spectral densities for the
operating Swiss-AlpArray stations during the period from September 2015 to
June 2016 divided in regions of installation (basins and mountains). Each
line represents a single station. The light grey lines correspond to the
NHNM and NLNM models, and the magenta thick line is the AlpArray noise level
requirement.
After data acquisition, an automatic procedure run nightly calculates the
distribution of seismic power spectral density (PSD) using the direct
Fourier method (Cooley and Tukey, 1965), using the PQLX software package
based on McNamara and Buland (2004). These probability density functions
(PDFs) of the PSD allow us to identify the ambient noise conditions as high
probability occurrences and it is nowadays a standard tool to examine
artefacts related to station operation, episodic cultural noise, the overall
station quality and the level of Earth noise at each site. The daily updates
of the PSDs for the Swiss-AlpArray stations are available at
PDF of vertical and E-W components for the site A061A
The sites on rock (in the mountains) show very good performances over the
whole broadband range, on average
Acceptable noise levels in sites located in densely populated basins are quite rare. It is well known that in the Po plain the seismic ambient noise is particularly strong (Marzorati and Bindi, 2006) and difficult to avoid. The general geological setting, site-effects and man-made activities make the noise level at high frequency one of the highest recorded throughout the whole experiment. High population density, high-speed trains, highways, industries, intensive agriculture and a surface geology characterized by loose sediment, clay and sand make it almost impossible to fulfil the noise level requirements, especially at high frequency. The coupling of traffic and machinery with the ground is the dominant source of high-frequency and propagates as high-frequency surface waves, with periods < 1–2 s, that attenuate within several kilometres from the source (e.g., Havskov and Alguacil, 2004). Similar conditions, even if slightly better, are found in the Pannonian and in the Zagreb basins. Therefore, most of our stations in sedimentary basins, with the notable exception of the long-period vertical components, do not meet the AlpArray noise requirements but they also do not exceed the NHNM level (Fig. 4c, d).
From qualitative comparison of our noise levels (Fig. 4c, d) to those at INGV permanent broadband stations in the Po Plain (Fig. 6b, c), we can conclude that our station setup generally performs as well as the nearby permanent installation for short periods, and even better for long periods (especially on the vertical component). When comparing the noise levels among these stations, however, it is important to note that sensor types and installations are not identical.
Median curves of the power spectral densities of the
three components for three operating INGV permanent stations in the Po Plain
basin (courtesy of CNT-INGV, Rome).
Stations A283B and A285A (Fig. 5e, f) at fairly “remote” sites in the Po Plain have a quite satisfactory noise level, especially at short periods (the long-period horizontal components are high due to building tilting). As a general characteristic we note that many of the sites show a peak of noise between 0.2 and 1.5 s and a remarkable diurnal variation of noise sources. This is particularly true for site A282A where a noisy industrial plant disturbs the area for kilometres around causing significant huge diurnal variation.
The deployment of STS-2 as the standard seismometer for our stations
facilitates collection of excellent long-period data even with temporary
sites. The STS-2 has lower noise levels at long periods than many other
broadband sensors (Wielandt and Streckeisen, 1982), still true today. This is
clearly seen when we compare the vertical long-period noise of a STS-2
(Fig. 5a–g) with a Nanometrics Trillium Compact 120 s (Fig. 5h), where the
improvement is typically about
With communication systems installed at each station, we are able to recover in real-time or quasi-real-time ca. 97 % of the data. The data at 100 sps and state of health (SOH) are continuously acquired (and also immediately archived) by the SED seismic network. 3–4 GB per month of data traffic in a usual mobile SIM-card is sufficient to guarantee the communication of all the data, also for the noisier stations in the Po Plain. The full data is also stored locally on flash drives that have the capacity to record over 6 months of data at our sampling rate. Any missing data are constantly attempted to be retrieved by a daily run python script that directly communicates with the digitizer. Still existing data gaps are definitively filled when the data are manually collected and stored in the EIDA database. In Fig. 7 we show the data availability of the 27 Swiss-AlpArray stations from real-time communication, from the installation day to the end of June 2016. Due to interruptions in station operation (power interruption for more than 1 week or serious problems with data logger and sensor) we have gaps of more than 2 weeks for the stations A060A, A272A, A283B and A288A. The advantage of having all the digitizers on-line and reachable is the possibility to monitor and react rapidly when problems are observed. We can, for example, re-centre the STS-2 masses from the office or check the remaining storage space available.
Data availability (green), as a function of time, of the 27 Swiss-AlpArray stations from real-time communications from the installation day to the end of June 2016. The gaps (red) are constantly filled once the data are manually collected and stored in the database. Large gaps for the stations A060A, A272A, A283A, A283B and A288A are not restorable because of station operation interruptions (mainly power interruption for more than one week or serious problems with data logger and sensor). Intermittent gaps are mainly due to connection problem (low bandwidth) and will be filled once the data are manually retrieved.
According to the AlpArray rules, the Z3 network code stations are
immediately available in real-time for registered seismological
observatories within the AlpArray boundaries with monitoring and alerting
duties (
The noise performances of our stations allows the clear recording of local and teleseismic events even at the noisier stations. In Figure 8 we show the waveform from a M3.5 local earthquake that occurred near Cuneo, Italy on the 13 March 2016, and a M7.8 teleseismic event that occurred on 2 March 2016 in Sumatra. Clear phase arrivals can be identified, demonstrating that the data can be used for earthquake location and for many of the project scientific purposes. An example of the earthquake location using the AlpArray data during routine seismic service at SED is shown in Fig. 9. At least 4 Z3-stations helped to reduce the azimuthal gap in the south. Such a uniform coverage of a wide region will help to decrease detection magnitude limits and reduce earthquake location uncertainty in many areas.
In addition, the SED Seismic Network offers a real-time monitoring system to track communications, power consumption, noise changes and data completeness for all the temporary AlpArray stations. Moreover, the regular calculation of the PSD curves allow us to monitor the noise situation at each site and promptly decide and intervene whenever is needed.
The principles and procedures described in this paper allow the collection of top quality seismological data in a densely populated region with challenging lithological subsurface conditions. This dataset will provide the means to address by state-of-art seismic methods important and exciting scientific questions on current geodynamics and the evolution of the Alps and to improve the seismic hazard assessment in the region.
Examples of waveforms recorded by the Swiss-AlpArray temporary
stations.
Location solution of the Poschiavo (Switzerland) M3.2 event occurred on 11 April 2016 calculated at the Swiss Seismological Service (SED-ETHZ). At least four AlpArray stations are used to improve the location and to fill the south gap. Green lines are manually detected Pg and Sg picks. The location procedures are performed using SeisComp3 software.
Our temporary stations performance, in general, meets the AlpArray Seismic
Network quality requirements in terms of noise level (i.e. 20 dB lower than
the NHNM for vertical components and 10 dB lower of NHNM for horizontal
component), with the exception of highfrequencies (> 1 Hz) for
stations in the sedimentary basins. All 27 stations we deployed are
characterized by a noise levels lower than the maximum NHNM. Sensors in the
Alps and Dinaridies show a noise level
Waveform data from all AlpArray Seismic Network (AASN) stations is available
through EIDA (
In the AASN, the permanent stations are contributed via the following networks codes: BW, CH (Swiss Seismological Service (SED) at ETH Zurich, 1983), CR, CZ (Institute of Geophysics, Academy of Sciences of the Czech Republic, 1973), FR (RESIF, 1995), CR, HU, G (Institut de Physique du Globe de Paris (IPGP), & Ecole et Observatoire des Sciences de la Terre de Strasbourg (EOST), 1982), GE (GEOFON Data Centre, 1993), GR, GU (University of Genova, 1967), HS, HU (Kövesligethy Radó Seismological Observatory, 1992), IU (Albuquerque Seismological Laboratory (ASL)/USGS, 1988), IV (INGV Seismological Data Centre, 1997), MN (MedNet project partner institutions, 1988), NI (OGS (Istituto Nazionale di Oceanografia e di Geofisica Sperimentale) and University of Trieste, 2002), OE, OX (OGS (Istituto Nazionale di Oceanografia e di Geofisica Sperimentale), 2016), PL, RD, RF (University of Trieste, 1993), SI, SK, SL, ST (Geological Survey-Provincia Autonoma di Trento, 1981), SX, TH.
Swiss-AlpArray Field Team: Irene Molinari (Institute of Geophysics, Department of Earth Sciences, ETH Zürich, 8092 Zürich, Switzerland), Eduard Kissling (Institute of Geophysics, Department of Earth Sciences, ETH Zürich, 8092 Zürich, Switzerland), Domenico Giardini (Institute of Geophysics, Department of Earth Sciences, ETH Zürich, 8092 Zürich, Switzerland), György Hetényi Institute of Earth Sciences, University of Lausanne, 1015 Lausanne, Switzerland), John Clinton (Swiss Seismological Service, ETH Zürich, 8092 Zürich, Switzerland), Stefan Wiemer (Swiss Seismological Service, ETH Zürich, 8092 Zürich, Switzerland), Florian Haslinger (Swiss Seismological Service, ETH Zürich, 8092 Zürich, Switzerland), Matteo Bagagli (Institute of Geophysics, Department of Earth Sciences, ETH Zürich, 8092 Zürich, Switzerland), Erika D. Erlanger (Institute of Geophysics, Department of Earth Sciences, ETH Zürich, 8092 Zürich, Switzerland), Pascal Graf (Swiss Seismological Service, ETH Zürich, 8092 Zürich, Switzerland), Robin Hansemann (Swiss Seismological Service, ETH Zürich, 8092 Zürich, Switzerland), Marcus Hermann (Swiss Seismological Service, ETH Zürich, 8092 Zürich, Switzerland), Paula Koelemeijer (Institute of Geophysics, Department of Earth Sciences, ETH Zürich, 8092 Zürich, Switzerland), Anne Obermann (Swiss Seismological Service, ETH Zürich, 8092 Zürich, Switzerland), Roman Racine (Swiss Seismological Service, ETH Zürich, 8092, Zürich, Switzerland), Korbinian Sager (Institute of Geophysics, Department of Earth Sciences, ETH Zürich, 8092 Zürich, Switzerland), Julia Singer (Institute of Geophysics, Department of Earth Sciences, ETH Zürich, 8092 Zürich, Switzerland), Robert Tanner (Swiss Seismological Service, ETH Zürich, 8092 Zürich, Switzerland), Sascha Winterberg (Institute of Geophysics, Department of Earth Sciences, ETH Zürich, 8092 Zürich, Switzerland), Andre Blanchard (Institute of Geophysics, Department of Earth Sciences, ETH Zürich, 8092 Zürich, Switzerland), Leonardo Colavitti (Institute of Earth Sciences, University of Lausanne, 1015 Lausanne, Switzerland), Tommaso Giardini (Swiss Seismological Service, ETH Zürich, 8092 Zürich, Switzerland), Josip Stipčević (Department of Geophysics, Faculty of Science, University of Zagreb, 10000 Zagreb, Croatia), Iva Dasović (Department of Geophysics, Faculty of Science, University of Zagreb, 10000 Zagreb, Croatia), Marijan Herak (Department of Geophysics, Faculty of Science, University of Zagreb, 10000 Zagreb, Croatia), Davorka Herak (Department of Geophysics, Faculty of Science, University of Zagreb, 10000 Zagreb, Croatia), Vesna Šipka (Republic Hydrometeorological Service of Republic of Srpska, 7800 Banja Luka, Bosnia and Herzegovina), Dejan Jarić (Republic Hydrometeorological Service of Republic of Srpska, 7800 Banja Luka, Bosnia and Herzegovina), Shasa Šikman (Republic Hydrometeorological Service of Republic of Srpska, 7800 Banja Luka, Bosnia and Herzegovina), Zoltán Wéber (Kövesligethy Radó Seismological Observatory, Geodetic and Geophysical Research Institute of the Hungarian Academy of Sciences, 1112 Budapest, Hungary), Zoltán Gráczer (Kövesligethy Radó Seismological Observatory, Geodetic and Geophysical Research Institute of the Hungarian Academy of Sciences, 1112 Budapest, Hungary), Stefano Solarino (Istituto Nazionale di Geofisica e Vulcanologia, 00143 Roma, Italy).
Irene Molinari coordinates, organizes and participates all the site scouting, station deployments, data quality control and prepared the manuscript with contributions from all co-authors. John Clinton manages data flow and quality control. Edi Kissling is the principal investigator of Swiss-AlpArray and AlpArray and supervises the project. György Hetényi participated in the initial phase of the project setup and station deployment, and manages the AlpArray Seismic Network. Domenico Giardini initiated the AlpArray project. Josip Stipčević, Iva Dasović and Marijan Herak scouted for sites and deployed the six seismic stations in Croatia, Vesna Šipka scouted and deployed the three seismic stations in Bosnia and Herzegovina. Zoltán Wéber and Zoltán Gráczer scouted and deployed the three seismic stations in Hungary. S. Solarino participated in the scouting and installations of 5 sites in Italy. The Swiss-AlpArray Field Team participates in the scouting, installation and maintenance of all Swiss-AlpArray stations. The AlpArray Working Group worked out the network layout, quality guidelines and standards for the seismic data exchange.
The authors are grateful to the
AlpArray Seismic Network Team
(