This diagram shows an example of T phase
recorded at Vaihoa (Rangiroa, French Polynesia)
from an Antarctic iceberg drifting in the Ross Sea.
The bottom diagram is
a time series of the ground velocity, high pass filtered at f > 2 Hz.
The main plot is a spectrogram contouring the energy in the record as a function
of time and frequency (scale in dB is given at bottom right).
The right plot
shows the raw spectrum of the full seismogram.
At frequencies greater than background noise (f > 2.5 Hz), note that the signal is
generally monochromatic, the spectral line being at 4 Hz (with harmonics present),
but that its frequency evolves slowly with time (increasing in the present example to
This time window corresponds to the ending phase of the signal, which on that particular day,
lasted more than 3 hours.
Return to Emile A. Okal's research page.