Observatories and Research Facilities for EUropean Seismology
Volume 1, no 2 April 1999 Orfeus Newsletter
Newsletter joint publication

The Regional Data Center at the Seismological Central Observatory Gräfenberg SZGRF

Klaus Stammler

Seismological Central Observatory Gräfenberg, Mozartstr. 57, D-91052 Erlangen, Germany. 
tel: +49 9131 81040-27, fax: +49 9191 81040-99 

Introduction - Stations and instrumentation - Data archive -
Access to waveform data - Detections - Locations and bulletins

Introduction

The SZGRF is the data center for data of the Gräfenberg-Array (GRF) and the German Regional Seismic Network (GRSN). GRF and GRSN are the two major broadband station systems within Germany. The 13 stations of the GRF array are located within an area of about 50 x 100 km east of the city of Nuremberg (Fig 1). It became operational in April 1980, although continuous recordings of the first subarray are available since 1976. The array is operated by the Seismological Central Observatory (SZGRF) which is part of the Federal Institute for Geosciences and Natural Resources (BGR). It is supported by the Deutsche Forschungsgemeinschaft (DFG). The GRSN project started in 1991 as a joint research project of BGR and geophysical institutes of German universities and was funded by the DFG. It was planned as an extension of the GRF array. In addition, the GRSN can be regarded as the German contribution to international initiatives aimed at the establishment of modern digital seismic broadband networks on a regional and global scale. The 13 GRSN stations plus 3 associated stations are distributed quite evenly over Germany (Fig 1). Digital data of GRF and GRSN are recorded and archived continuously since installation up to now.

Fig 1. Map with station of the GRSN (black traingles) and GRF (green dots)

Stations and Instrumentation

The instrumentation of GRF and GRSN is:

  • GRF:
    • 13 stations GRA1, GRA2, GRA3, GRA4, GRB1, GRB2, GRB3, GRB4, GRB5, GRC1, GRC2, GRC3, GRC4
    • STS-1 BB-seismometers
    • 3 3-component and 10 vertical instruments
    • flat velocity response between 5 Hz and 20 s
    • 16-bit gain ranging digitizers (dynamic range 132 dB, resolution 66 dB)
  • GRSN:
    • 16 stations BFO, BRG, BRNL, BSEG, BUG, CLL, CLZ, FUR, GRFO (IRIS/GRSN), GSH, IBBN (assoc.), MOX, RGN (assoc.), STU (assoc.), TNS, WET
    • 15 STS-2 BB seismometers and 1 KS36000 borehole BB instrument (station GRFO)
    • 3-component instruments
    • flat velocity response from 40 Hz to 120 s (STS-2) and 5 Hz to 360 s (KS36000)
    • 24-bit Quanterra Q860 data loggers

Fig 2. Seismometer station of the Gräfenberg array

Fig 3. Seismometer vault of a Gräfenberg station

Data Archive

All data are recorded and archived continuously since installation. The first digital stations of the GRF array were installed in 1976, the array was completed in 1980. The GRSN was started in August 1991 with 8 stations and was extended 1993, 1994 and 1996 to the current number of stations. The data are archived on CD-Recordables, some are on tape (DAT, Exabyte). Most of the CD-Recordables are in two 500-CD-Jukeboxes and permit automated access from inside and outside of the SZGRF (Table 1).

Table 1: Available data at the SZGRF
Stream time span continuous Jukebox
GRF 20 Hz Jul.1976 - Dec.1979 yes not yet
GRF 20 Hz Jan.1980 - now yes yes
GRSN 1 Hz Jan.1992 - now yes yes
GRSN 20 Hz Aug.1991 - now yes yes
GRSN 80 Hz Jan.1997 - now no yes
GRSN 80 Hz Aug.1991 - now yes no

All 20Hz and 1Hz data are continuously on CD and available for automated access (except GRF from 1976-1979, currently). The continuous 80 Hz data of the GRSN are mostly on tape, some more recent on CD, but only a few selected events of local events in Germany are in a jukebox. So data requests on these 80Hz data can be processed only in a few cases.

The data are transmitted to the SZGRF via digital dial-up lines (ISDN) and the GRSN data also by tapes. The GRF data are copied several times a day, so the most recent are between 1 and 6 hours old. The 20Hz and 1Hz GRSN data are transmitted once at night (European time), transmission gaps on GRSN data are not recovered, so the data may be incomplete. The complete GRSN data set including the 80Hz streams comes after 2-4 weeks on tapes.

Access Methods to Waveform data

The SZGRF runs two automated interfaces for waveform data requests. One is the AutoDRM developed at the Swiss Seismological Service (SSS), the other is a request form on WWW. The AutoDRM is an e-mail based request manager. It accepts specially formatted e-mails, processes the requests and sends the data back by e-mail or, preferably for large files, by anonymous ftp. Start with a mail 'please help' or read the manuals at the SSS: The output format of the AutoDRM is always GSE2.0 (cm6-compressed). A mail example for requesting 5 minutes of GRF z-components is:

BEGIN
EMAIL [your-email-address]
STA_LIST GRF
CHAN_LIST BHZ
TIME 1995/08/17 01:08:00.0 TO 1995/08/17 01:13:00.0
WAVEFORM GSE2.0
STOP
    

The homepage of the SZGRF allows requests via WWW. It will show a request form for selection of stations, channel, component, start time, copy length and out put format. Available output formats are currently SEED, Mini-SEED (data records only), GSE1.0, GSE2.0 and SAC. CSS3.0 is in preparation. After submitting the request it is immediately processed and after some time (seconds or minutes depending on the size of the request) a message will tell that a result file has been prepared and is ready for ftp. With one more mouseclick the transmission by anonymous ftp from the WWW page to the local computer is started. Note that we currently have only a digital 64kBit connection to the Internet, please be patient when transmitting larger files.

Of course, we also accept request lists by e-mail. Please send it to Uta Mundl or Klaus Stammler. Please specify a station list (GRF and/or GRSN or single station names), components (z or zne), channel (BH=20Hz or LH=1Hz), output format (SEED, Mini-SEED, GSE1.0, GSE2.0 or SAC) and a time window list. The window list should have one time window per line, the time window given by copy start time (format: 23-may-1996_22:45:05 or equivalently 23,5,1996,22,45,5 or 1996/5/23,22,45,5) and the number of seconds to copy, separated by one or more blanks. Do not use blanks within the start time. We also need to know which exchange media to use (CD-Recordable, DAT tape, Exabyte tape or ftp).

Automatic Detections

The data of GRF and GRSN are scanned by automatic detection algorithms. The resulting longperiod and shortperiod detections lists are made available on the Web-Site of the SZGRF.

Preliminary Locations and Bulletins

All detected and recorded local and teleseismic events are manually analyzed on a daily basis. Phase readings, preliminary locations, periods, amplitudes and different magnitudes are stored in a database (INGRES). The homepage of the SZGRF allows requests to this database creating listings of various types over a specified time window. Additionally, manually revised local and teleseismic bulletins are available. The are organized as monthly files and are created with a time delay of less than 4 weeks.

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Copyright © 1999. Orfeus. All rights reserved.