Digital seismic event recorders: Description and examples from the San Jacinto fault, the imperial fault, the Cerro Prieto fault, and the Oaxaca, Mexico subduction fault

Abstract

abstract Digital seismic event recorders in use by the Centro de Investigacion Cientifica y Educacion Superior de Ensenada (CICESE) and by the University of California, San Diego (UCSD) are described. The field-recording systems consist of Kinemetrics 5-sec period seismometers and Geotech 1-sec period seismometers operating with Terra Technology digital event recorders, clock synchronizer, and field playback unit. The basic recorders (DCA-3009s) were modified to provide lower power consumption and greater amplification. The data handling facility consists of a laboratory playback unit which spools data directly into the PRIME computer at CICESE. The playback unit can also be interfaced with a PDP-11 minicomputer to produce data on magnetic tape in a form useful for analysis on the PRIME. The software available includes search and edit capabilities on the PDP-11, and search, edit, timing, and spectral analysis capabilities on the PRIME. Data are shown illustrating that, in the environments studied, very simple seismograms are observed for some events. This indicates that much of the complexity observed in other seismograms (for earthquakes in nearly the same location) is either due to the radiation pattern having a node for S waves in the direction of the station or due to complexity in the source. The quality of the data obtained from digital event recorders promises to yield important results concerning the nature of source complexity and the nature of rupture propagation and high-frequency radiation. These results will, in time, be valuable for understanding and modeling earthquake strong motion.