Appendix 1


Terms used on Estimation Charts, Diagrams And in the Text

b Apparent explosions or sharp bursts of tremor. not affecting tremor amplitudes before or after event.
R Volcanic tremor, narrow frequency range 1 to 3 c/s.
Rb Apparent explosions or sharp burst of tremor simultaneous with start of tremor.
Rc Chuffing tremor, appears apparently during dying phase of activity.
Rd Volcanic tremor of wide frequency range, sometimes with rapidly varying power spectrum.
Rf Volcanic tremor of mixed high (9 to 12 c/s) and low (1 to 3 c/s) frequencies, occurring for short periods.
Rh Harmonic tremor, as (Wh) on all records made before 9.9.67 and known as whistle phenomena. A high frequency harmonic of R, directly related to gas emissions of the volcano concerned.
L Local earthquake distance between 30 and I000 km, indicated by time interval between P and S arrivals.
VL Very local earthquake distance less than 30 km, indicated by time interval between P and S arrivals.
P Deep earthquake. P sharp compared to S arrival.
W Wind and rain.
X Instrumental, not seismic.
M Microseisms, as for oceans and lakes.
A Artificial man made noises.

Seismic Events Interpreted as of Volcanic Origin with Relation to Frequency Spectrum

1 c/s to 3 c/s Volcanic tremor (R), dominant frequency 1 c/s to 2 c/s.
1 c/s to 5 c/s Apparent explosions (b and Rb), dominant frequency 1 c/s tu 2 c/s
1 c/s to 7 c/s Volcanic tremor (Rd), dominant frequencies between 1 c/s and 3 c/s.
9 c/s to 12 c/s Volcanic tremor of high frequency (Rf) normally superimposed on tremor (R).

Average Amplitude of Volcanic Tremor (R)

Amplitude ranges of (R) mentioned in text and in Figures 2, 3 and 5, are readily taken from the initial evaluation charts. The approximate equivalent amplitude of the ground motion at 2 c/s from February 20, 1966.

High: 0.6 microns and above.

Medium: 0.4 to 0.6 microns.

Low: up to 0.4 microns.

These levels were determined by test signals between 40 and 400 microvolts fed Into the tape seismograph input, and the corresponding ground amplitudes have been taken from the calibration charts as shown in the manual for the Willmore seismometer.

Go to Download page for seismic audio files and discussion by G.R.T. Clacy

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