SHAKEALERT: Closing the NOTA GNSS Coverage Gap Along the Oregon Coast

The Network of the Americas (NOTA), funded by the NSF and operated by UNAVCO, includes 1150 GNSS stations federated into a single hemispherical-scale network from stations of the former EarthScope Plate Boundary Observatory, COCONet, and TLALOCNet networks. While NOTA was originally designed using 24-hr daily files, it has proven valuable to stakeholders who use real-time data for early warning systems and other applications. In Cascadia, UNAVCO and the Pacific Northwest Seismic Network (PNSN) have been working to incorporate high-rate, high-precision GNSS data into the USGS-funded ShakeAlert project. The geodetic component of ShakeAlert consists of equipment upgrades, improved telemetry, hardening power systems, enhanced real-time data handling, and installation of 5 new stations to provide early warning for a large magnitude earthquake. The earthquake early warning (EEW) algorithm requires 4 to 6 stations to resolve spurious point source triggers. A GNSS station coverage gap was identified along the Oregon coast based on existing NOTA station locations and planned PNSN seismic installations. UNAVCO and University of Oregon (UO) PNSN staff collaborated on siting, permitting, and construction of new stations. The process to install the additional stations began in late 2019. Two of the new sites (EUCH and NOSE) are co-located with existing PNSN seismic stations. COVID protocols and travel restrictions imposed significant delays on both permitting and construction. The permits for EUCH and NOSE were obtained in late 2020, but weather and travel restrictions delayed construction until March 2021. The construction for new site YACH was completed in three short months, from recon in February 2021 to construction in May 2021. The new sites at MZNT, EUCH, YACH, and AGNS are driven-braced monuments, while NOSE is a short, drilled-braced monument. All sites are equipped with Tallysman VC6000 GNSS choke ring antennas and Septentrio PolaRx5 receivers with onboard Precise Point Positioning (PPP) enabled. This two-year project to install these sites resulted in improved GNSS data coverage in Oregon and will enhance public safety from earth hazards. Its completion highlights the outstanding relationship between UNAVCO and UO PNSN, as well as the operational expertise that UNAVCO provides to our community.