Geodetic techniques involving spaceborne measurement have revolutionized scientific understanding of Earth surface deformation, and this thesis presents several independent methodological developments concerning such data. The primary results are: a more general method for the optimal design of geodetic networks; an algorithm for detecting transient deformation events in large geodetic datasets; the identification of a previously unmapped fault in the San Francisco Bay Area, California; a new approach to quantifying the permeability structure of shallow, near-surface, strike slip faults; and a regional evaluation of correlated seasonal deformation in the Bay Area. These results are not strictly related, however, several themes are present throughout. Particular emphasis is placed on the development of statistical and numerical methodology. Although the results presented in this thesis are not strictly related, they represent a significant contribution to our scientific understanding of Earth surface deformation phenomena.

Societal and economic losses in earthquakes are strongly dependent on the strength of shaking of the ground. Such shaking, or ‘ground motion’ can vary widely from place to place for a given earthquake based on characteristics of the earthquake source, crustal properties affecting seismic wave behavior, and differences in the strength of near-surface geologic material. We investigate the variability in ground motion through a range of methods and techniques and address several of these parameters (e.g., source, path, or site effects) that influence seismic hazard in tectonically active regions, namely: King County in Washington State, U.S. near the Cascadia subduction zone, Bío Bío in Chile near the Atacama Trench, and Christchurch, New Zealand near the Pacific-Australian plate boundary. To study these variations in ground motion, we utilize computational simulations of earthquake hazard and economic loss using the FEMA HAZUS (Federal Emergency Management Agency HAZards U.S) model and seismic data acquired through high-density deployments of small, low-cost micro-electro-mechanical-systems (MEMS) Quake-Catcher Network (QCN) accelerometers. While these sensors are lower-resolution compared to traditional, more expensive seismometers, our results suggest that, with appropriate quality control, QCN sensors provide good-quality data that can be integrated with local networks. We propose that the more economical MEMS sensor technology can drive future studies of seismic hazard and risk at higher spatial resolution than previously available and, with ample amounts of seismic data collected (i.e., “big data”), is posed to revolutionize modern seismology.

The Geysers geothermal field in northern California has seen subsidence, attributed to net volume loss during power production, since at least the 1960s. Over the last three decades this has been accompanied by reductions in reservoir steam pressure and power generation. To combat these effects, wastewater has been injected in the field since 1997. In order to better understand the effects of variations in production and wastewater injection on geothermal reservoir volume and surface subsidence over time, two continuously-recording GPS stations (TG01 and TG02) in the northern Geysers in 2012 and one in the southern Geysers (TG03) in 2013 were installed in the field.

In this thesis, I will present our first analyses of the continuous GPS data and our first attempt at modeling the data. Both TG01 and TG02 show early periods of uplift and later subsidence while TG03 shows ongoing subsidence. Next, we downsample steam extraction and injection data onto a rectangular grid and calculate ‘observed’ monthly volume changes as a function of position. We then use these to drive a forward elastic dislocation model to predict surface deformation changes each month in The Geysers field. The models cannot reproduce the GPS data, specifically the uplift that occurs at TG01. We then compare the observed volume changes with inverse elastic dislocation models of the volume changes required to reproduce the GPS time series. Due to low spatial resolution, we compare the total volume change in the field, which is comparable amplitude, and shows periods where the peaks are in phase, and periods where they are out of phase. In these cases, the peaks in the inverse modeled volume changes lag those in the reported data by one month. These 'out-of-phase periods' correlate with periods of peak injection in the field, typically in the winter and early spring months, suggesting that the GPS data are detecting a delayed deformation response to injection in the field, possibly related to the finite permeability of the geothermal reservoir rocks.

We also look at a case study of The Geysers Mw 5.0 earthquake. This earthquake is a rare small shallow strike-slip earthquake capable of producing surface displacements. Our three continuous GPS stations in the field recorded coseismic displacement of up to 2 cm. We also were able to see the earthquake displacement in a 6-day descending interferogram. We ran forward and inverse models of both nodal planes provided by earthquake catalogs and found that both nodal planes produce consistent deformation patterns although the inverse model closely matched the NNW-striking nodal plane.

Fault creep is a behavior of some faults where the two sides of a fault slowly slide past one another in the absence of large earthquakes. This is a form of aseismic slip and can be continuous or episodic. Understanding what drives fault creep is important as it can reduce the amount of strain that accumulates in the crust and can impede future earthquake ruptures. Both of these aspects play an important role in analyzing the seismic hazard of a region, therefore mapping the extent of where fault creep is occurring and identifying common lithology between creeping faults is necessary for accurate hazard assessment.

In this dissertation, we focus on fault creep in northern California using three different methods -- satellite imagery, 3D models derived from photographs, and rock mechanics experiments. In the first project, we focus on mapping the extent of fault creep along on two faults in the North Bay (north of the San Francisco Bay Area), the Maacama and Rodgers Creek faults. Both faults have observations of fault creep at specific locations but the extent and variability of fault creep on each fault is not well mapped. We use Interferometric Synthetic Aperture Radar (InSAR) to map the extent of fault creep along both faults and estimate at least 55% of the Maacama fault and 40% of the Rodgers Creek faults are creeping at the surface.

The second project focuses on offset sidewalk observations along the southern Hayward Fault, known to be creeping at rates up to ~8 mm/yr and how fault creep is being expressed in an urban setting. We construct 3D models from 2D photos taken from 2015 to 2018 to measure 3D displacements of each offset sidewalk. In this way we can monitor how the fault is being expressed in an urban environment due to the creeping fault. We find that on average, individual offset curbs sample < 40% of the overall creep rate measured from nearby alignment arrays (which span a fault-perpendicular distance of 100 m or more). In some locations, multiple adjacent curbs are actively deforming. These findings imply that there is significant off-fault deformation along the southern Hayward fault, and suggests that the `fault trace' can more correctly be considered a zone of deformation, narrower than an alignment array width but wider than one curb length.

The third and fourth projects center on an exposure of the Bartlett Springs fault core near Lake Pillsbury, which is known to be creeping at 3.4 mm/yr from a nearby alignment array. We collected the fault gouge and ran two sets of experiments to investigate the frictional and mineralogical properties needed for a fault to creep. The first set of experiments investigated which of the minerals that we found in the fault gouge, are promoting or not promoting fault creep. We find that the presence of talc has the strongest influence on creep behavior. The second set of experiments explored the frictional properties of the natural fault gouge and compared their frictional properties to samples collected from the creeping section of the San Andreas fault. We found that both fault gouges have similar compositions and frictional properties. In order for fault creep to occur on the Bartlett Springs fault, we estimate that there needs to be at least 50% talc in the gouge, concentrated into layers in which the majority of shear is taking place.

Through the various approaches to understanding fault creep used in this dissertation and the compilation of previous studies using various techniques (e.g. GPS-derived models, seismology, additional geodetic observations), we have a better understanding of fault creep mechanisms and distribution in the North Bay. We estimate a larger extent of the Maacama and Rodgers Creek faults to be creeping than previously observed, supplementing previous estimates from repeating earthquake families, GPS-based models, alignment arrays, and prior InSAR studies in the area. The measurement of offset sidewalks along the Hayward fault shows along-strike variations in the rates of movement but also allows us to quantify how much of the total creep occurs in a narrow zone near the mapped surface trace (3-10 meters wide) versus the wider zone measured by alignment arrays (~100 meters wide). The low frictional strength of talc within the Bartlett Springs fault gouge is the main driving factor of fault creep on the fault, and can promote creep at depths up to 9 km. The mineral assemblage is also similar in its elemental composition to the fault gouge collected within the creeping section of the San Andreas fault, suggesting that the creep in both places is controlled by a similar lithology sampled by each fault. This suggests that the Bartlett Springs fault may also be creeping at deeper depths, up to 9 km, consistent with the depths of repeating earthquakes located on the fault.

Rapid, Robust Characterization of Subduction Zone Earthquakes