- Email: [email protected]
The “Soufriere” system: PC-based instrumentation for acquiring and processing data from seismograph networks
47
Tectonophysics, 209 (1992) 47-49
Elsevier Science Publishers B.V.. Amsterdam
Extended abstract
The “Soufriere” system: PC-based instrumentation for acquiring and processing data from seismograph networks D. Beckles a, J.B. Shepherd
b and W.P. Aspinall ’
a Richards Computer Products, Dales, High Street, Didcot, Oxon OX1 I SEQ, UK b Institute of Environmental and Biological Sciences, Uniu. of Lancaster, Lancaster LA1 4YQ, UK ’ Aspinall & Associates, 3 Cypress Court, Harris Way, Sunbury-on-Thames, TW16 7EL, UK
(Received February 13, 1991; revised version accepted July 27, 1991)
A PC-based system which collects earthquake data in digital form from telemetered networks of short-period and long-period seismograph stations has been developed. The system is supported by a family of programs for the on-line monitoring and collection of signals, analysis of the stored signals and picking of phase arrivals, routine hypocentral determination and the production of seismic bulletins. Included also is a facility for the off-line archiving of the signals. The major sub-systems in the family are: MONITOR for on-line seismic event detection; PLAYBACK for the inspection and analysis of stored traces and construction of phase arrival records; WURST for hypocentral calculations and production of bulletins; SAVIDX for archiving saved traces; JHD for joint hypocentral determinations; EPIDRAW for interactive display of the locations of hypocentres. A number of algorithms can be applied to incoming signals in MONITOR to discriminate between genuine earthquake signatures and various types of noise. Discriminants are based on the
Correspondence
to: W.P. Aspinall, Aspinall& Associates, 3 Cypress Court, Harris Way, Sunbury-on-Thames, TW16 7EL, UK.
0040-1951/92/$05.00
Fast Fourier transform, the Walsh transform or the Walsh dyadic-shift invariant transform, and can be adjusted for different noise conditions on individual data channels. The performance of the chosen detection algorithm and user-set parameters can be tested on sample data using the program SIMULATE. From PLAYBACK, the seismograph signals are available for inspection in near real-time on a graphics screen, from which phase arrival times can be read and sent to a relational data base for processing. A number of waveform analysis tools are available under this program: digital filters; Fourier spectrum analysis; particle motion plots for three-component data, and seismometer response calibration. The related data processing package performs all the tasks required by a seismological observatory: hypocentral locations are estimated by the flexible interactive program WURST and can be relocated using the method of Joint Hypocentral Determination (JH;D). A full data base management system is included, which archives original digital seismograms (SAVIDX), arrival time data, earthquake locations and other related information in easily retrievable form. Among the facilities provided by the program is full screen data entry, with complete editing of phase arrival, station co-ordinate and enrth model information. All the data are held lin files of variable length with keyed sequentfal access. Throughout the data base, various standard iden-
0 1992 - Elsevier Science Publishers B.V. All rights reserved
-180 -190 -200 -210
-3
-
a
0
u
, 100
I
0
I 200
a
t
I 300
DISTANCE
1
I 400
1 5 IO
Ckm)
Fig. 1. East Caribbean seismicity: raw data 1980-1990.
code found in the IX Bulletin. Events are identified by a seven-digit code, in which the first four digits usualiy, but not necessarily, represent the
tifiers have been adopted: stations are identified by a four-character code, consisting of upper-case letters and digits, which, in most cases, is the -10
-
-20
-
-30
-
-40
-
cl
-50 -
';‘ Y t"
-60
-
-70
-
-80
-
-90
-
-100
-
-110
-
-120
-
-730
-
-140
-
-150
-
-so
-
-170
-
-1eo
-
-190
-
-200
m
/ 0
,
I
t
Cl
/ 200
100 DISTANCE
/
I 300
{km)
Fig. 2. East Caribbean seismic&: northern area, 1980-1990.
I 400
ACQUIRING AND PROCESSING DATA FROM SEISMOGRAPH
NETWORKS
year and month of the event, while the last three represent a sequence number. Each Earth model is identified by a name which may be up to sixteen characters in length, while for seismic phases the conventions of the ISC Bulletin are used. Seismological bulletins, including maps of earthquake locations, are easily produced and three-dimensional displays of hypocentres can be manipulated on the graphics screen with EPIDRAW. Hardware requirements are modest. The complete system will run on a single IBM PC-AT or compatible machine with any graphics display and 80287 math co-processor, although two machines will be needed if continuous acquisition is to be undertaken. When two machines are used, fast data transfer from the monitor to the playback machine is effected over a special parallel port link. Alternatively, data can be transferred by diskette, exchangeable hard disk or by a communications link. The Soufriere System includes various utility programs for supporting system housekeeping, diagnostics and similar activities, and hardcopy output can be provided on dot-matrix or laser printer.
49
The system has been extensively tested on the Eastern Caribbean telemetered network for several years for both routine monitoring of regional seismic activity and for the study of volcanic earthquake sequences. It has proved to be exceptionally robust during intense bursts of seismic activity. As an example of its application to regional seismicity studies, Figure 1 shows a depth cross-section of preliminary hypocentres in the Leeward Islands from 1980 to 1990, using phase arrival data picked interactively on the Soufriere System; the section is approximately normal to the trend of the island arc. For comparison, Figure 2 shows hypocentres of events which have been relocated using the Joint Hypocentral Dete~ination option in the Soufriere System; only the solutions that converge satisfa~toriily are plotted but these give a much sharper image of the Benioff-Wadati subduction zone in this area. This refined information has been used to define source zones more accurately for seismic hazard assessment.
Tectonophysics, 209 (1992) 47-49
Elsevier Science Publishers B.V.. Amsterdam
Extended abstract
The “Soufriere” system: PC-based instrumentation for acquiring and processing data from seismograph networks D. Beckles a, J.B. Shepherd
b and W.P. Aspinall ’
a Richards Computer Products, Dales, High Street, Didcot, Oxon OX1 I SEQ, UK b Institute of Environmental and Biological Sciences, Uniu. of Lancaster, Lancaster LA1 4YQ, UK ’ Aspinall & Associates, 3 Cypress Court, Harris Way, Sunbury-on-Thames, TW16 7EL, UK
(Received February 13, 1991; revised version accepted July 27, 1991)
A PC-based system which collects earthquake data in digital form from telemetered networks of short-period and long-period seismograph stations has been developed. The system is supported by a family of programs for the on-line monitoring and collection of signals, analysis of the stored signals and picking of phase arrivals, routine hypocentral determination and the production of seismic bulletins. Included also is a facility for the off-line archiving of the signals. The major sub-systems in the family are: MONITOR for on-line seismic event detection; PLAYBACK for the inspection and analysis of stored traces and construction of phase arrival records; WURST for hypocentral calculations and production of bulletins; SAVIDX for archiving saved traces; JHD for joint hypocentral determinations; EPIDRAW for interactive display of the locations of hypocentres. A number of algorithms can be applied to incoming signals in MONITOR to discriminate between genuine earthquake signatures and various types of noise. Discriminants are based on the
Correspondence
to: W.P. Aspinall, Aspinall& Associates, 3 Cypress Court, Harris Way, Sunbury-on-Thames, TW16 7EL, UK.
0040-1951/92/$05.00
Fast Fourier transform, the Walsh transform or the Walsh dyadic-shift invariant transform, and can be adjusted for different noise conditions on individual data channels. The performance of the chosen detection algorithm and user-set parameters can be tested on sample data using the program SIMULATE. From PLAYBACK, the seismograph signals are available for inspection in near real-time on a graphics screen, from which phase arrival times can be read and sent to a relational data base for processing. A number of waveform analysis tools are available under this program: digital filters; Fourier spectrum analysis; particle motion plots for three-component data, and seismometer response calibration. The related data processing package performs all the tasks required by a seismological observatory: hypocentral locations are estimated by the flexible interactive program WURST and can be relocated using the method of Joint Hypocentral Determination (JH;D). A full data base management system is included, which archives original digital seismograms (SAVIDX), arrival time data, earthquake locations and other related information in easily retrievable form. Among the facilities provided by the program is full screen data entry, with complete editing of phase arrival, station co-ordinate and enrth model information. All the data are held lin files of variable length with keyed sequentfal access. Throughout the data base, various standard iden-
0 1992 - Elsevier Science Publishers B.V. All rights reserved
-180 -190 -200 -210
-3
-
a
0
u
, 100
I
0
I 200
a
t
I 300
DISTANCE
1
I 400
1 5 IO
Ckm)
Fig. 1. East Caribbean seismicity: raw data 1980-1990.
code found in the IX Bulletin. Events are identified by a seven-digit code, in which the first four digits usualiy, but not necessarily, represent the
tifiers have been adopted: stations are identified by a four-character code, consisting of upper-case letters and digits, which, in most cases, is the -10
-
-20
-
-30
-
-40
-
cl
-50 -
';‘ Y t"
-60
-
-70
-
-80
-
-90
-
-100
-
-110
-
-120
-
-730
-
-140
-
-150
-
-so
-
-170
-
-1eo
-
-190
-
-200
m
/ 0
,
I
t
Cl
/ 200
100 DISTANCE
/
I 300
{km)
Fig. 2. East Caribbean seismic&: northern area, 1980-1990.
I 400
ACQUIRING AND PROCESSING DATA FROM SEISMOGRAPH
NETWORKS
year and month of the event, while the last three represent a sequence number. Each Earth model is identified by a name which may be up to sixteen characters in length, while for seismic phases the conventions of the ISC Bulletin are used. Seismological bulletins, including maps of earthquake locations, are easily produced and three-dimensional displays of hypocentres can be manipulated on the graphics screen with EPIDRAW. Hardware requirements are modest. The complete system will run on a single IBM PC-AT or compatible machine with any graphics display and 80287 math co-processor, although two machines will be needed if continuous acquisition is to be undertaken. When two machines are used, fast data transfer from the monitor to the playback machine is effected over a special parallel port link. Alternatively, data can be transferred by diskette, exchangeable hard disk or by a communications link. The Soufriere System includes various utility programs for supporting system housekeeping, diagnostics and similar activities, and hardcopy output can be provided on dot-matrix or laser printer.
49
The system has been extensively tested on the Eastern Caribbean telemetered network for several years for both routine monitoring of regional seismic activity and for the study of volcanic earthquake sequences. It has proved to be exceptionally robust during intense bursts of seismic activity. As an example of its application to regional seismicity studies, Figure 1 shows a depth cross-section of preliminary hypocentres in the Leeward Islands from 1980 to 1990, using phase arrival data picked interactively on the Soufriere System; the section is approximately normal to the trend of the island arc. For comparison, Figure 2 shows hypocentres of events which have been relocated using the Joint Hypocentral Dete~ination option in the Soufriere System; only the solutions that converge satisfa~toriily are plotted but these give a much sharper image of the Benioff-Wadati subduction zone in this area. This refined information has been used to define source zones more accurately for seismic hazard assessment.