Recent great earthquakes and ensuing tsunamis in Sumatra, Chile and Japan have demonstrated the need for accurate full spectrum ground displacements that more completely characterize the great amplitudes and broad dynamic range associated with these vast, complex ruptures. Our ability to model these events, whether in real-time or after the fact, is limited by the weaknesses of both seismic and geodetic networks. Geodetic instruments provide the static component as well as coarse dynamic motions, but are much less precise than seismic instruments, especially in the vertical direction. Seismic instruments, in turn, provide exceptionally-sensitive dynamic motions, but typically have difficulty recovering unbiased near-field static offsets and low-frequency motions because of contamination, for example, from instrument tilt. The three-year project proposed here demonstrates a new paradigm for studying the processes of large earthquakes and the hazards they pose by integration of geodetic and seismic measurements at the observational level to produce accurate three-dimensional broadband displacements and velocities that span the full spectrum of seismic motion, whether in the near- or far-field. The main objectives are to (1) demonstrate using historical data in subduction zone and strike slip environments that the optimal combination of geodetic and seismic data at the observational level significantly improves finite-fault slip inversions, (2) investigate appropriate methodologies to perform efficient full (dynamic+static) waveform inversions, (3) create a test bed of 15 integrated GPS/seismic stations along the southern San Andreas fault system as a prototype for further expansion along the Western North America plate margin and integration into PBO operations, and (4) determine its capabilities and limitations through comparisons of observation noise levels with the desired sensitivity level determined from simulated ruptures. Through a single proposal involving personnel from Scripps Institution of Oceanography and UNAVCO, items (1), (2), and (4) are proposed for funding by the EarthScope program, while item (3) is proposed for funding by the Instrumentation and Facilities program.
The project leverages the considerable infrastructure already invested in the EarthScope project and responds to the EarthScope science plan for the next decade, a plan that calls for the enhancement of the EarthScope facilities in response to evolving science needs, and the recommendations resulting from the 2012 real-time GPS workshop sponsored by UNAVCO. The project also leverages considerable ongoing investments by NASA over the last decade in software, hardware, and algorithms for rapid earthquake response and structural monitoring based on GPS/seismic integration, and seed funding through NSF (Geophysics and Engineering programs) for low-cost hardware upgrades to facilitate GPS/seismic integration.
Intellectual Merit. This is a collaborative project to demonstrate to the EarthScope community that a new interdisciplinary data type - full spectrum displacements based on an optimal combination of geodetic and seismic data - can significantly improve finite fault slip modeling through full waveform inversion of the earthquake source, as well as contribute to rapid characterization of earthquakes and their tsunamigenic potential. It will provide new data for researching earthquake processes, crustal strain and deformation, and other science applications. We will add low-cost MEMS accelerometer packages to PBO stations along the southern San Andreas fault system. A practical outcome will be a demonstrated and validated approach that could be used to upgrade many more existing PBO and other continuous stations in Western North America with significantly improved capabilities. All raw and analyzed data as well as algorithms and related software will be freely and openly accessible for real-time as well as post processing applications.
Broader Impacts. The broader impacts of GPS/seismic integration are significant in terms of scientific value, engineering infrastructure, civilian use, and economic impact. The network contributes directly to natural hazards research and early warning systems for earthquakes, volcanoes and tsunamis, to atmospheric research including short-term weather forecasting and related flooding hazards, to calibrations of satellite radar imagery and ionosphere monitoring, and to earthquake engineering research for large structures (e.g., bridges, buildings, dams) with very long-period response. By providing a source of freely available real-time data, the network also contributes to civilian applications requiring precise real-time positioning (e.g., surveying, GIS, agriculture, intelligent transportation) and hence contributes to economic stimulus. Finally the project supports collaborative and interdisciplinary research, education of technologically sophisticated graduate students, strengthening of diversity in support of workforce development, and enhancement of curricula at a variety of levels through engagement of new types of data sets that have direct societal impact.