Geology topics
Publications and source records attributed to James N. Murdock.
The analysis of individual movement choices can be used to better understand population-level resource selection and inform management.
A signal detector and analyzer algorithm was described by Murdock and Hutt in 1983. The algorithm emulates the performance of a human interpreter of seismograms. It estimates the signal onset, the direction of onset (positive or negative), the quality of these determinations, the period and amplitude of the signal, and the background noise at the time of the signal. The algorithm has been coded in C language for implementation as a 'blackbox' for data similar to that of the China Digital Seismic Network. A driver for the algorithm is included, as are suggestions for other drivers. In all of these routines, plus several FIR filters that are included as well, floating point operations are not required. Multichannel operation is supported. Although the primary use of the code has been for in-house processing of broadband and short period data of the China Digital Seismic Network, provisions have been made to process the long period and very long period data of that system as well. The code for the in-house detector, which runs on a mini-computer, is very similar to that of the field system, which runs on a microprocessor. The code is documented.
A new short-period event detector has been implemented on the Seismic Research Observatories. For each signal detected, a printed output gives estimates of the time of onset of the signal, direction of the first break, quality of onset, period and maximum amplitude of the signal, and an estimate of the variability of the background noise. On the SRO system, the new algorithm runs ~2.5x faster than the former (power level) detector. This increase in speed is due to the design of the algorithm: all operations can be performed by simple shifts, additions, and comparisons (floating point operations are not required). Even though a narrow-band recursive filter is not used, the algorithm appears to detect events competitively with those algorithms that employ such filters. Tests at Albuquerque Seismological Laboratory on data supplied by Blandford suggest performance commensurate with the on-line detector of the Seismic Data Analysis Center, Alexandria, Virginia.
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A seismic refraction experiment was conducted in the metamorphic belt of central California during May 1972. Seven charges were fired during the experiment. Three seismic refraction lines, 75 to 125 km long, were made in the belt. Also, data were gathered for regional travel-time calibrations. The experimental data are presented. They include P-wave travel times, station locations, shot locations, and shot origin times.
An array of eight seismic stations was operated at Castaic, California during the winter of 1972-1973. Forty-two earthquakes with M < 2.6 were located within or near this network which was 10 km in radius. Twelve of the events occurred in Ventura Basin, twenty-four occurred in Ridge Basin, and six occurred in the borderlands east of Ridge Basin. The events ranged in focal depth from 3 to 20 km, and the deepest of them were in Ventura Basin. The locations of these events are tabulated together with the P and S arrival times, the P polarities, and estimates of the quality of the locations. The locations of the hypocenters are accurate to within several kilometers.