Seismological Observatory, Geodetic and Geophysical Research Institute, Budapest, Hungary
In Hungary, regular seismological observations started at the beginning of the 20th century. Since that time the seismological station network have been reconfigured several times because of various (financial, conceptual, political) reasons.
In the last 15 years remarkable development has been occurred in Hungarian seismology. First the number of stations increased from 4 to 15 in 1995 when the Paks Microseismic Monitoring Network (Paks MMN) was established on the order and with the financial support of the Paks Nuclear Power Plant Ltd.
The second period of the development process had been initiated by the project MEREDIAN coordinated by ORFEUS. During and since this period the number of broadband stations have been raised from 1 to 6. The know-how and software products that were distributed all over Europe mainly by this project have made possible the real-time data exchange between partner institutions, too. This way not only the Virtual European Broadband Seismograph Network could be created but also each of the national agencies included our institute could form their own virtual networks.
A brief history of the last decade
At the beginning of the last decade of the 20th century there were only 3 seismograph stations in operation in Hungary. In 1994 the number increased to 4 with the opening of the new short period digital station GYL. At this moment there was one station with traditional analogue recording (BUD), one broadband station with continuous digital recording (PSZ), and two short period digital stations with event recording only (GYL, SOP).
In 1995, there has been substantial progress with development of the Hungarian earthquake monitoring network. With considerable investment the Paks Nuclear Power Plant Ltd. established a network of high quality digital seismographs, following the recommendations of the International Atomic Energy Agency. With this investment the number of seismic stations raised to 15 in Hungary (Fig. 1). In the following years the geometry of the Paks Microseismic Monitoring Network was modified a few times. For the first time, this network made it possible to detect and locate such low magnitude local seismic events that it is very unlikely so as to felt events go undetected in most parts of the country.
Fig. 1. Number of stations of the Seismological Station Network in Hungary as it developed with time
In 1997 the status of station PSZ changed: it became a part of the permanent station network of GEOFON. On this occasion the station received a new PC with SeisComP software. This time station PSZ had only dial-up connection. Internet connection was established two years later permitting real-time data access.
In 2001 our institute was invited to participate in project MEREDIAN2. This project was a special amendment to the MEREDIAN (Mediterranean-European Rapid Earthquake Data Information and Archiving Network) EC project started earlier. Our participation in this project has brought a significant upgrading to our network. During this period (2002-2005) station PKSM received new broadband instrumentation and Internet connection. This station started its broadband operation in February, 2004. But perhaps it was even more important to receive software packages and knowledge, and also the continuous assistance of the partners in the improvement of our seismic station network. Since the beginning of our participation in this project we could manage to have 4 additional broadband stations (SOP, BUD, BEHE, TRPA) in our country (Fig. 1).
Seismograph stations in operation in 2006
There are 15 seismological stations in Hungary operated by two different institutions: Geodetic and Geophysical Research Institute (GGRI) and GeoRisk Earthquake Research Institute Ltd (Table 1, Fig. 2). The two institutions share all the measured data. FDSN network code is HU; ISC and NEIC network code is BUD. The schematic structure of the network can be seen in Fig. 3, data flow is plotted in Fig. 4.
Table 1. Seismic stations
Fig. 3. Structure of the station network
Fig. 4. Data flow
Short period instrumentation
At the moment there are 9 short period stations in operation, eight of them belong to the Paks Microseismic Monitoring Network. All these stations have Lennartz LE3D-1s seismometers and Lennartz MARS88 data loggers. At 5 of the stations (PKS2, PKS6, PKS7, PKS9, PKSN) we use on-site recording on magneto-optical discs. Data are collected regularly twice a month.
At the remaining 4 stations the MARS88 data loggers are connected to PCs with SeisComP running on them. The plugin that made this connection possible had been created by Aladino Govoni (m88_plugin). Three of the stations (PENC, PKSG, PKSO) have near real-time data access via Internet using the SeedLink protocol. Data latency is between 10 and 25 minutes due to the operation schedule of the plugin. One station (RHK3) also uses SeedLink protocol for the data transfer but it has dial-up telephone connection therefore there can be an additional delay in data access.
Six broadband stations have been installed in Hungary so far. All these stations has Streckeisen STS-2 very broadband seismometers. All stations have EarthData PS-6-24 digitizers except station PKSM where we use a Quanterra Q380 unit as a digitizer. At all the stations Linux PCs are used as data acquisition units with SeisComP software running on them. All stations have Internet connection for data transfer. At station TRPA WLAN connection is used. The average data latency at these stations is below 10 s.
Software packages SeisComP and SeedLink developed at GEOFON became a kind of standard all over Europe recently. Because of this fact it became rather easy to access near real-time data of stations of partner institutions. This way one can extend the national network beyond the political borders creating an extended, virtual network of seismic stations (Table 2). The larger pool of data provided by this extended or virtual network helps to have faster and more accurate earthquake locations and parameter determinations. The map of the recent configuration of the virtual network used at our data center can be seen on Fig. 5.
Fig. 5. Map of the virtual network used for earthquake location at Budapest data centre (for details see Table 2).
Table 2. Virtual network stations
The data centre of the Hungarian station network is located in Budapest. At the data centre a SeedLink server is operated. Real-time data from broadband stations can be accessed through this server. Real-time data are provided to international data centers (ORFEUS, GEOFON) and some partner institutions. Seismogram readings (phase data) are disseminated by means of e-mail. AutoDRM service is also available (email@example.com). A kind of live seismograms are generated in every 10 minutes and are published on our Hungarian Seimological Observatory web-site. The results of the automatic location system (Autoloc1 by GEOFON) can be found on this web-page, too.
In the last 15 year history of the Hungarian seismological station network two periods of major development can be found. The first one took place in 1995 when a new short period digital network of 11 stations was established. This network used event recording only and most of the stations had on site recording. Still, the overall detection capability of the Hungarian station network had increased significantly with this expansion. The second important extension of the network started in 2002 when our institute joined the MEREDIAN project. During this period the number of broadband station raised from 1 to 6. Besides, the knowledge and the software packages we could gain with our participation made it possible to improve some of the short period stations, too, having continuous recording and near real-time data access.