2. High-Gain Long-Period Seismograph System - HGLP: [ HG ]

DATES OF OPERATION:  	01 Sep 1972 to 17 Jul 1978

SEISMOMETER TYPE:
Teledyne-Geotech long period 3 component system, Model S-11 vertical and two 
Model S-12 horizontals.  Seismometers are located in sealed metal tanks filled 
with argon gas.

DIGITAL FORMAT:
16 bit integer data words for all components.  Range: +32,767 to -32,768 counts.

EVENT DETECTOR ALGORITHM:  None

Click on any of the following items for further information.

• Channel Data
• Amplitude Response to Ground Velocity
• Seismic Noise Study graph information
  • Seismic Noise Level - Annual
  • Seismic Noise Level - Seasonal/Diurnal

COMMENTS:
The HGLP Seismograph Network was the first global network of digitally recording
seismograph stations.  Installations began in August, 1972, and the last system
was closes in 1979.  The initial hardware included long period photo-tube amplifiers
(PTA) which had inherent drift problems which in turn affected the calibration.  
The PTAs were replaced with Ihtaco amplifiers in early 1975 which resulted in a
standard response curve for the HGLP Network. All of the data was recorded on 7
track magnetic tape, and forwarded to the Albuquerque Seismic Laboratory for 
processing and data quality review.  In 1985 all of the HGLP data was re-recorded 
on 9 track magnetic tape in SRO format.  This data is now available in the SEED
format, however, it should be noted that the calibration for much of the data 
is suspect.

Ithaco amplifiers were installed 12 Dec 1974.
Seismic background noise is similar to that for ANMO.  During windy conditions 
the noise is higher.