Optimal Network Geometry for PBO

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The systematic design of geodetic networks has not received much attention in the literature because of the difficulty in formulating the problem while incorporating known error sources and source complexity. Identifying an optimal network design becomes particularly important for the Plate Boundary Observatory (PBO) given the scale of the proposed network. As the geodetic community begins the installation phase of PBO, there exists a window of opportunity to optimize the network design through the modification of station placements. By optimizing the proposed network geometry, the quality of data from PBO will be improved and hopefully allow for the greater resolution of tectonic and volcanic events.The proposed network geometry for PBO is being evaluated through a series of numerical simulations based on the scientific objectives of the PBO initiative. Three characteristic events have already been simulated: an aseismic transient on the central San Andreas fault, a slow earthquake on the Cascadia subduction interface, and a propagating dike at Mount St. Helens. Results for transient source models describe the PBO network performance as a function of the magnitude and duration of an event and provide insight on the expected level of resolution. Additional scenarios investigated in this work include conduit models of magma transport and steady-state deformation along the plate boundary. For each simulation, synthetic GPS data are created that include formal white noise and a random walk component. The Extended Network Inversion Filter is used to infer the original source parameters from synthetic time series data given the proposed station distribution. The Extended Network Inversion Filter is an implementation of a Kalman filter that is well suited to extract a time-dependent signal from noisy data and is efficient at analyzing large time-series data sets. Resolution of the source process is evaluated by comparing the synthetic input model with the inferred source model estimated by the filter. Additional analysis evaluates the optimal instrument ensemble (i.e. GPS and borehole strainmeters) and the optimal density of stations required to resolve a given source process. Recommendations derived from this work will be communicated directly with the PBO manager and standing committee.