deployed in the framework of AlpArray in March 2015 (blue dots). Of the total 276 temporary AlpArray stations, 73 stations were included in PACASE and then in AdriaArray – see the constant difference between the two curves in 2016-2019. In May 2019, the PACASE deployment started, providing additional 62 stations. AdriaArray inherited in total 135 stations from these two previous experiments. Since the start of AdriaArray in May 2022, 293 additional temporary stations have been installed to reach 428 temporary AdriaArray stations operating anytime after May 2022, of which 417 are in EIDA and are thus included in _ADARRAY. In addition, 5 permanent stations were installed in Ukraine.

Assembling this plot required quite complex analysis of the history of each station. It is important to note that _ADARRAY only includes stations, which were operational during the AdriaArray epoch, i.e., anytime after 19. May 2022. Stations closed before this date are not included in the plot. Hence, the plot does not show the total number of stations operational at a given date, but shows only a number of those stations, which remained operational until and during the AdriaArray epoch. We used the startDate of the `<Station>` element from the metadata to create the plot. However, there are several cases, when we manually reconsidered this startDate. Stations using two network codes simultaneously (and hence included two times in the _ADARRAY) are taken into account only once for the plot using the older startDate in case the two dates differ. Stations which have used more station codes in the past are given with the oldest startDate. This applies to both temporary as well as to permanent stations. For example, stations which continued to AdriaArray from PACASE are given with the startDate of the PACASE deployment, and those, which merged to PACASE from AlpArray and then merged to AdriaArray from PACASE are

<figure><img src="image_17.png" /></figure>

**Figure J1.** Virtual _ADARRAY in time and space. Starting dates of stations included in the virtual _ADARRAY network are used to plot a cumulative number of operating stations over 37 years, from the beginning of 1988 till June 2025. Orange are permanent and blue are temporary stations added on top of the permanent. The two curves split in the moment when the AlpArray deployment started in March 2015. Then, the difference between the curves increases again in May 2019 when the PACASE deployment began. Since June 2022, AdriaArray delivered additional 293 temporary stations. Together with the temporary stations continued from PACASE, the AdriaArray Seismic Network includes 428 temporary stations currently, out of which 417 are in EIDA and hence included in the _ADARRAY – see the difference between the two curves at the right end of the plot. The inserted map shows the distribution of permanent and temporary stations in the AdriaArray region.
given with the original AlpArray startDate, regardless of their network codes. Similarly, for example stations of the
permanent NI network, which were merged to the OX network are given with their original NI startDate.

There are temporary AdriaArray stations built at the same sites, which were used previously for AlpArray, either
keeping the original AlpArray station name, or being given a new one. For these stations, the startDate of the
AdriaArray deployment is shown as these stations were discontinued and hence are considered as newly built for
AdriaArray. Permanent stations, which were upgraded with broadband instruments for AdriaArray are shown as
temporary (blue triangles in Fig. J1) with the startDate of the upgrade. Temporary stations, which were moved to the
“B” site during the AdriaArray epoch are shown with the older “A” site startDate, regardless of the fact that the “A” site
was deployed during the AdriaArray epoch or during any older experiment of AlpArray or PACASE. Stations, which
were moved to the “B” site during previous experiments AlpArray and PACASE are given with their “B” startDate,
as the original “A” site is not included in the _ADARRAY. Stations, which were originally built as temporary and
later became permanent, are included in the permanent set (orange triangles), with the original startDate of the
temporary deployment. The latter case is difficult to track, as both the network code and the station name changed
and hence the fact that it is the same station is not easily recognizable. Although the _ADARRAY includes only
broadband stations, some of the permanent stations could be equipped with a short-period instrument for some
epochs in the past. These changes of instrumentation are not reflected in the plot.

*CORRESPONDING AUTHOR: Petr KOLÍNSKÝ,*

Institute of Geophysics of the Czech Academy of Sciences, Prague, Czech Republic

e-mail: petr.kolinsky@ig.cas.cz

© 2025 the Author(s). All rights reserved.

Open Access. This article is licensed under a Creative Commons Attribution 4.0 International