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I. Regional Variations in Upper Mantle Compressional Velocities beneath Southern California. II. Post-Shock Temperatures: Their Experimental Determination, Calculation, and Implications

Citation

Raikes, Susan Ann (1978) I. Regional Variations in Upper Mantle Compressional Velocities beneath Southern California. II. Post-Shock Temperatures: Their Experimental Determination, Calculation, and Implications. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/3323-8080. https://resolver.caltech.edu/CaltechTHESIS:04142020-164137815

Abstract

The establishment in Southern California of a large seismographic network provides an unique opportunity for studying the seismic velocity variations within a tectonically active region that includes a major plate boundary, whose surface expression is the San Andreas Fault. In the first part of this thesis, the compressional velocity within the upper mantle beneath Southern California is investigated through observations of the dependence of teleseismic P-delays at all stations of the array on the distance and azimuth to the event. The variation of residuals with azimuth was found to be as large as 1.3 sec at a single station; the delays Here stable as a function of time, and no evidence was found for temporal velocity variations related to seismic activity in the area. These delays were used in the construction of models for the upper mantle P-velocity structure to depths of 150 km, both by ray tracing and inversion techniques. The models exhibit considerable lateral heterogeneity including a region of low velocity beneath the Imperial Valley, and regions of increased velocity beneath the Sierra Nevada and much of the Transverse ·Ranges. These changes are attributed to variation in the degree of partial melting within the upper mantle; their relationship to, and implications for, regional tectonics are discussed in the final chapter of this section.

One of the major uncertainties in the interpretation of shock wave data is the temperature reached under shock compression and subsequent release. The second half of this thesis describes the development of a technique for the experimental determination of post-shock temperatures, its application to several metals and silicates shocked to pressures in the range 5 to 30 CPa. The technique utilises an infra-red radiation detector to determine the brightness temperature of the free surface of the sample after the shock wave has passed through it, and has yielded highly reproducible results that are consistent for the wavelength ranges 4.5 to 5.75 and 7 to 14µ. The comparison of these results with values calculated using conventional theories provides some insight into the thermal processes occurring in shock waves. In particular, the measured temperatures are generally higher than those calculated; this is attributed to elasto-plastic effects in metals, and is probably associated with strength effects in silicates, both of which are commonly ignored in the calculation of theoretical temperatures. The implications of these observations for the interpretation of shock-induced metamorphism and impact phenomena, and for the application of shock-wave data to the interpretation of the behaviour of silicates within the earth's mantle, are discussed in the final chapter.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Geophysics
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Geophysics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Unknown, Unknown
Thesis Committee:
  • Unknown, Unknown
Defense Date:23 May 1978
Funders:
Funding AgencyGrant Number
Fluor CorporationUNSPECIFIED
IBMUNSPECIFIED
NSFDES75-03643
USGS14-08-0001-15893
USGS14-08-0001-16711
NASANGL 05-002-105
Record Number:CaltechTHESIS:04142020-164137815
Persistent URL:https://resolver.caltech.edu/CaltechTHESIS:04142020-164137815
DOI:10.7907/3323-8080
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13675
Collection:CaltechTHESIS
Deposited By: Melissa Ray
Deposited On:15 Apr 2020 16:58
Last Modified:20 Apr 2020 22:32

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