In this dissertation, we explore how high-rate displacement data from Global Navigation Satellite Systems (GNSS) sensors can be used in combination with other instrumentation, including strong-motion accelerometers and seafloor geodetic sensors, for applications to near-shore tsunami early warning and structural monitoring of earthquakes. Accurate estimates of fault slip amount and along-strike rupture extent are necessary for determining the coastal extent of high-amplitude tsunami waves. We describe how these values can be estimated using static slip inversions of coseismic data from GNSS sensors used in conjunction with seafloor coseismic data from hypothetical offshore networks. We find that a trench-parallel profile of offshore stations over the deformation front is an optimized offshore network for this approach. We find that the most accurate slip estimates require horizontal seafloor coseismic data which is currently not feasible to obtain in real time. We then explore how using existing real-time technology -- high-rate GNSS as well as onshore and offshore three-component strong-motion accelerometers -- could be used in a rapid hypothesis test of modified kinematic slip inversions to confirm the depth of slip location of a megathrust earthquake given that shallow earthquakes produce the most dangerous tsunamis.

If the GNSS sensors and accelerometers are collocated, their data can be combined in a Kalman filter to produce seismogeodetic waveforms: broadband displacements that contain the high-frequency information from the accelerometers and low-frequency and static offset information from the GNSS sensors. As the GNSS and seismic monitoring networks were developed independently, many of these stations are not collocated. We compare with a shake table experiment how Micro-Electro-Mechanical Systems (MEMS) accelerometers perform relative to observatory-grade accelerometers at frequencies of interest, and evaluate their applicability to upgrading existing GNSS sensors into seismogeodetic stations for earthquake early warning and rapid response purposes. This experiment demonstrated the utility of the combined seismogeodetic data for structural monitoring, and we provide an example applying seismogeodetic instrumentation to record in-situ building motion for an aging reinforced concrete structure in Oklahoma, an oil producing region that is currently experiencing high rates of induced seismicity.