Accession Number : AD0633304

Title :   HIGHER MODES OF SEISMIC SURFACE WAVES: MODE SEPARATION,

Corporate Author : UPPSALA UNIV (SWEDEN) SEISMOLOGICAL INST

Personal Author(s) : Crampin,Stuart ; Bath,Markus

Report Date : AUG 1964

Pagination or Media Count : 21

Abstract : A digital computer is used to filter seismograms in order to separate the higher modes from each other and from fundamental modes and microseisms. The filtered traces show higher modes for a longer time than the original seismogram and modes may be visible which were previously undetected. Mode separation results in some alterations to dispersion curves measured from original seismograms. These changes are minor in the majority of cases when only the second mode is recorded on the seismogram but may be important when several modes are present. Without mode separation it is very difficult to distinguish visually between the crests and troughs of two higher mode wave trains when they arrive simultaneously. The filtering has revealed the existence of a 'coda' to the higher mode wave trains similar to the well-known 'coda' of the fundamental mode Rayleigh waves. The channel waves are usually seen as amplitude increases on the filtered traces. (Author)

Descriptors :   (*SEISMOLOGY, *DATA PROCESSING), EARTHQUAKES, MICROSEISMS, SEISMIC WAVES, WAVE ANALYZERS, DIGITAL COMPUTERS

Subject Categories : Seismology
      Computer Hardware

Distribution Statement : APPROVED FOR PUBLIC RELEASE