Open AccessBroadband modelling of regional seismograms: Imperial Valley to Pasadena
Author(s) -
Helmberger D.,
Stead R.,
HoLiu Phyllis,
Dreger D.
Publication year - 1992
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.1992.tb00711.x
Subject(s) - seismogram , geology , seismology , broadband , rayleigh wave , waveform , directivity , surface wave , telecommunications , optics , physics , radar , computer science , antenna (radio)
SUMMARY This paper addresses broadband wave propagation along a corridor from Imperial Valley to Pasadena, California. The path consists of 50 km of slow basin structure with a shallow Moho followed by 250km of relatively normal southern California structure approaching Pasadena. Events occurring in the valley produce extended body wave codas which carry a dispersive waveform imprint along with longer period Rayleigh waves. Many features of these seismograms at periods greater than a few seconds can be modelled by applying a finite‐difference technique to a 2‐D structure. Shorter periods display complex behaviours not easily modelled by present techniques, especially for shallow events. Events occurring in the normal structure produce broadband SH ‐waveforms that can be modelled, analytically, if some extra empirically derived alignment parameters determined from calibration events are used. These parameters are determined by adjusting traveltime differentials between the decomposed wavefield S, sS , etc. For example, delays in sS relative to S correspond to local corrections for sediment cover for a particular source region. Source complexity such as asperities and directivity become increasingly important at shorter periods, as demonstrated by numerical experiments and observation.