Extending Resolution of Fault Slip With Geodetic Networks Through Optimal Network Design

Geodetic networks consisting of high precision and high rate Global Navigation Satellite Systems (GNSS) stations continuously monitor seismically active regions of the world. These networks measure surface displacements and the amount of geodetic strain accumulated in the region and give insight into the seismic potential. SuGar (Sumatra GPS Array) in Sumatra, GEONET (GNSS Earth Observation Network System) in Japan, and PBO (Plate Boundary Observatory) in California are some examples of established networks around the world that are constantly expanding with the addition of new stations to improve the quality of measurements. However, installing new stations to existing networks is tedious and expensive. Therefore, it is important to choose suitable locations for new stations to increase the precision obtained in measuring the geophysical parameters of interest. Here we describe a methodology to design optimal geodetic networks that augment the existing system and use it to investigate seismo-tectonics at convergent and transform boundaries considering land-based and seafloor geodesy. The proposed network design optimization would be pivotal to better understand seismic and tsunami hazards around the world. Land-based and seafloor networks can monitor fault slip around subduction zones with significant resolution, but transform faults are more challenging to monitor due to their near-vertical geometry. Plain Language Summary Earthquakes and associated natural hazards expose a great number of people to significant risks. Despite tremendous efforts to precisely monitor fault activity, it is still challenging with the limited number of GNSS stations. In order to save cost and effort, we present a robust nonlinear optimization scheme to identify the optimal distribution of GNSS networks augmenting their current configuration. We explore the capacity of GNSS networks to monitor slip before, during, and after earthquakes to better prepare for anticipated ruptures and other aseismic fault activity. We realize a fundamental limitation of geodesy to monitor vertical strike-slip faults, motivating new complimentary ways to monitor these faults. Strong constraints on fault slip near the trench can be established using an extension of the GNSS data offshore, using sea geodesy. The proposed networks would allow monitoring of fault kinematics with improved accuracy.