I. Studies in crustal deformation using GPS and tiltmeters. II. New statistical techniques in static stress triggering

The topics covered by this dissertation are seemingly quite disparate: continuous Global Positioning System (GPS) geodetic measurements made on land, long-baseline tiltmeter measurements made on the seafloor, and studies of stress interactions following a large earthquake in southern California. However, all these subjects are variations on the theme of studying crustal deformation over a variety of spatial and temporal scales and in a range of tectonic environments.;Chapter 1 briefly lays out the general theory behind the use of GPS in studying crustal deformation and then applies it to a seven-year record of continuous GPS measurements in southern California. The chapter gives detailed histories for the sites used, and then focuses on describing the effects on the data set of various alterations in processing technique, as well as the temporal and spectral characteristics of the particular data set used.;Chapter 2 describes the theory of operation and the development of a long-baseline fluid-tube tiltmeter for use in the seafloor environment. The chapter's primary focus is the data returned from an operational deployment of four such tiltmeters on Axial Seamount on the Juan de Fuca Ridge. The work in the chapter shows that, while further development is needed to lower the noise level in the instrument, this tiltmeter design is currently capable of resolving deflation events associated with volcanism on active seamounts and segments of the Mid-Ocean Ridge system.;Chapter 3 discusses static stress interactions and their impact on regional seismicity following a large earthquake. The main focus is on development of a new statistical method for confirming the existence of such triggering. This method begins by computing the Coulomb stress changes experienced by a set of earthquakes spanning the occurrence of a mainshock. It then uses the Kolmogorov-Smirnov test to compare the distribution of stress changes for earthquakes after the mainshock to that for shocks preceding it; stress triggering is indicated if the distributions are different. This test is applied to the 1987 Superstition Hills earthquake sequence in southern California; the results show that significant triggering occurred following the mainshock of that sequence.