- Email: [email protected]
A low power portable seismic recorder
232
A LOW POWER PORTABLE
SEISMIC RECORDER
K. J. MUIRHEAD Research School (A us tralia)
of Physical
Sciences,
Australian
National
University,
Canberra,
A.C.T.
For many applications the use of portable seismic recorders which can be left in the field for long periods have inherent advantages over more conventional portable instruments which can only be deployed for a limited time duration. Thus although the need for such instruments has long been apparent, the many attempts to design them have only been partially successful principally because of the power requirements needed to drive both the recording media and a stable crystal clock. These problems have been overcome in the A.N.U. portable seismic recorders which can record signals continuously on a 2,400-ft magnetic tape for periods in excess of one month using a set of eight No.6 dry cells. Long term recording is accomplished by using a very slow tape speed of 0.01 inches/set. The seismic signals are recorded on the first two channels with a gain separation of 26dB giving a total dynamic range in excess of 70dB. Reliable timing of event onsets is obtained by recording both the output of a binary coded crystal clock and radio time signal on the third and fourth channels. With a crystal block stability of better than 0.05 set/d any recorded event can be timed to this accuracy provided the clock can be calibrated against radio time signals about once per day. Ten of these instruments have been assembled and have proved highly reliable in crustal and upper mantle experiments and also in monitoring micro earthquake activity around several dams.
IMPLICATIONS OF BLOT’S THEORY FOR THE PREDICTION VOLCANIC ERUPTIONS AND EARTHQUAKES
OF
J.C. GROVER John
Grover
and Assoc.,
Seaforth,
N.S. W. (Australia)
Derived in 1962 from valid observations based wholly on internationallyaccepted seismological data for the New Hebrides volcanoes, Blot’s Theory has given rise to a long list of volcanic predictions which have been officially confirmed. The prediction in June for the eruption in November 1963 of Gaua, a vol-
A LOW POWER PORTABLE
SEISMIC RECORDER
K. J. MUIRHEAD Research School (A us tralia)
of Physical
Sciences,
Australian
National
University,
Canberra,
A.C.T.
For many applications the use of portable seismic recorders which can be left in the field for long periods have inherent advantages over more conventional portable instruments which can only be deployed for a limited time duration. Thus although the need for such instruments has long been apparent, the many attempts to design them have only been partially successful principally because of the power requirements needed to drive both the recording media and a stable crystal clock. These problems have been overcome in the A.N.U. portable seismic recorders which can record signals continuously on a 2,400-ft magnetic tape for periods in excess of one month using a set of eight No.6 dry cells. Long term recording is accomplished by using a very slow tape speed of 0.01 inches/set. The seismic signals are recorded on the first two channels with a gain separation of 26dB giving a total dynamic range in excess of 70dB. Reliable timing of event onsets is obtained by recording both the output of a binary coded crystal clock and radio time signal on the third and fourth channels. With a crystal block stability of better than 0.05 set/d any recorded event can be timed to this accuracy provided the clock can be calibrated against radio time signals about once per day. Ten of these instruments have been assembled and have proved highly reliable in crustal and upper mantle experiments and also in monitoring micro earthquake activity around several dams.
IMPLICATIONS OF BLOT’S THEORY FOR THE PREDICTION VOLCANIC ERUPTIONS AND EARTHQUAKES
OF
J.C. GROVER John
Grover
and Assoc.,
Seaforth,
N.S. W. (Australia)
Derived in 1962 from valid observations based wholly on internationallyaccepted seismological data for the New Hebrides volcanoes, Blot’s Theory has given rise to a long list of volcanic predictions which have been officially confirmed. The prediction in June for the eruption in November 1963 of Gaua, a vol-