Long period channel waves from records of Friuli (Italy) earthquakes in 1976

Abstract

We present a study of a group of long period waves excited by the
earthquakes of Friuli (Italy) in 1976 and recorded between longitudinal
and transverse body waves by Long-period seismographs at epicentral
distances up to about 3 000 Km. The spectral analysis has permitted us
to determine periods of the main phases which make up the wave group.
In regard to the longer period phase, which appears first in the recordings,
the velocity obtained by the dromochrones equals 8.4 Km/s. The group
velocity is instead 7.4 Km/s. Such phases have been considered as being
longitudinal channel waves in the astenosphere. Such hypothesis explains
the inconsistencies which had appeared in previous studies on channel
waves in the astenosphere.