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