PBO provides raw and processed data products to users in the form of GPS velocities and time series of GPS positions and strain measurements. GPS results to date show a precision of less than a 1 mm (horizontal) and 2.5 mm (vertical) similar to, or better than, other CGPS networks such as the Southern California Integrated GPS Network (SCIGN) or the Japanese GeoNet project. GPS velocities are expressed in the Stable North American (SNARF) and IGS05 reference frames, the former developed by a UNAVCO working group of community geodesists that relies on GPS stations in the central and eastern United States (including 16 PBO stations) and Canada. The reference frame is obtained through a rigorous combination of independent solutions and accounts for glacial isostatic adjustments. The ability of PBO to address its scientific goals relies heavily on continuous instrument operation to obtain uninterrupted time series of positions and strain, which is critical for rigorously quantifying measurement errors and detecting transient deformation.
PBO borehole strainmeters provide direct measurements of earth strain. Strainmeter data products include fully corrected and scaled tensor and linear strain time series. Strainmeters are critical in determining the strain associated with ETS events especially those with no GPS signature and tidal modulation of slow slip in Cascadia (Hawthorne and Rubin, JGR in press).
PBO spans the North American continent with instrumentation providing the detailed deformation data necessary to address a wide range of scientific goals at the forefront of tectonics and earthquake science, including:
Fault properties and the earthquake process.
How do earthquakes start, propagate, and stop? How does strain accumulate and how is it released along the boundaries and within the North American plate? What structural and geological factors control earthquake generation along plate boundaries such as the San Andreas Fault and Cascadia and give rise to intraplate regions of seismic hazard such as the New Madrid zone?
Magma migration and volcanic hazard.
How can better methods be developed for the prediction of volcanic eruptions and hazard mitigation? How does magma originate and how is it transported in the subsurface?
Crustal strain transfer.
What kinds of transient movements occur at depth? How do crust and mantle rheology vary with depth or with distance from an active fault? What influence does this have on seismic and aseismic deformation? How does it vary near active fault zones and affect the earthquake process? How do faults inter- act with one another? What is the state of stress in the lithosphere?
Convergent margin processes and volatile cycling.
What is the nature of the plate boundary megathrusts in the Pacific Northwest and Alaska and how does it affect the seismic cycle? What is the structure of the deeper slab and how does it affect earthquakes and the overall subduction process? How is strain partitioning accomplished in the forearc and what controls it? What are the distributions and effects of subducted volatiles?
Continental structure and evolution.
What is a continent? How does continental lithosphere form and evolve? How are continental structure and deformation related? What is the lithospheric strength profile and what controls it? What is the composition of the lithosphere and how are fluids distributed through it?
Continental deformation and asthenospheric structure.
What are the spatial and temporal scales of intra- plate deformation? What are the forces driving continental deformation? How is the evolution of continental lithosphere related to upper mantle processes? How and where are forces generated in the upper mantle and how and where are they transferred to the crust?
Deep Earth structure.
What is the nature of the lower- most mantle? What are the heat budgets of the core, deep mantle, and lithosphere?