A Study of the Seismic Waves SKS and SKKS. Glacial Geology of the Frying Pan River Drainage, Colorado

Citation

Nelson, Robert Leslie (1952) A Study of the Seismic Waves SKS and SKKS. Glacial Geology of the Frying Pan River Drainage, Colorado. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/WWWD-0T60. https://resolver.caltech.edu/CaltechTHESIS:02082018-131502507

Abstract

[Major Thesis Abstract]

Arrival times, amplitudes, and periods of the seismic phases SKS and SKKS have been investigated for normal, intermediate, and deep earthquakes recorded at Pasadena and Huancayo, Peru. New observed time­-distance curves are constructed for depths of < 60, 100, 200, and 600 kilometers. Travel-times for the core have been calculated from normal shock time data. Slight modification of wave velocity just inside the core and of travel times within the core are suggested. Calculated travel times of SKS, SKKS, and SKKKS are in good agreement with observations.

Energy parameters determined from observed ampli­tude/period ratios are found in only fair agreement with those calculated from theory. Observed energies are too large for most of the phase components and depths considered. The horizontal components of SKKS over the whole distance range, and of SKS at Δ < 100°for all depths, yield observed energies less than those pre­dicted by theory. Both discrepancies are at least qual­itatively explained by a proposed non-spherical distribution of shear strain about the fault source, and by . abnormal absorption in the outer 700 kilometers of the core. A period increase with epicentral distance for SKS and SKKS is best explained by selective absorption in this same zone.

Anomalous observed energies, as a function of epi­central location, can also be accounted for by the proposed non-spherical distribution of energy. A similar regional phase-period dependence is considered in terms of finite faulting velocities. Times, energies, and periods of multiple SKS phases for the depths studied are presented. No single hypothesis commensurate with all observed conditions is found, but the phases pSKS and sSKS for normal shocks are probably represented.

[Minor Thesis Abstract]

On the west flank of the Sawatch Range, Colorado, evidence is found for six distinct glacial advances. One glaciation is pre-Wisconsin, four are Wisconsin, and one post-Wisconsin in age. In addition to end and lateral moraines of each advance, terrace remnants of six valley trains were identified and studied for a distance of 25 miles along Frying Pan River and its major tributaries. Elevations above stream level of these outwash terraces are 400±50, 90-120, 40-50, 20-30, 12-17, and 6-8 feet. Five of the tributary valleys contained ice streams which did not join the trunk Frying Pan glacier during the Wisconsin stage.

An extensive review and testing of the numerous criteria used to distinguish deposits of multiple glaciations shows that nine of these criteria can conveniently be expressed in parameters indicative of relative age. Estimates based on these criteria, coupled with a recent radiocarbon dating of late Mankato till in the Midwest, yield the following approximate ages for deposits of the six glaciations in Frying Pan Valley: 230,000, 63,000, 46,000, 17,000, 11,500, and 5,750 years. The accuracy and reliability of the procedure used cannot be evaluated without further absolute Carbon-14 age determination.

Thesis Files