Real-Time GNSS Positioning Along Canada’s Active Coastal Margin
Abstract:High-rate, low-latency Global Navigation Satellite System (GNSS) data are being refined for real-time applications to monitor and report motions related to large earthquakes in coastal British Columbia. Given the tectonic setting of Canada’s west coast, specific goals for real-time regional geodetic monitoring are: (1) the collection of GNSS data with adequate station density to identify the deformation field for regional earthquakes with M>7.3; (2) the robust, continuous real-time analyses of GNSS data with a precision of 1-2 cm and a latency of less than 10s; and (3) the display of results with attending automated alarms and estimations of earthquake parameters. Megathrust earthquakes (M>8) are the primary targets for immediate identification, since the tsunamis they generate will strike the coast within 15 to 20 min. However, large (6.0<M<7.5) normal or strike-slip earthquakes when occurring within the ocean plate offshore could be mistakenly identified as large-scale tsunamigenic events and need to be discriminated from subduction thrust ruptures in order to avoid tsunami “false alarms” and unwarranted mitigation responses.
Locally-produced results from the commercial software packages RTD and RTnet are augmented by real-time precise point positioning streams for regional sites received from the Canadian Geodetic Survey (CGS), the Jet Propulsion Laboratory (JPL), and the Plate Boundary Observatory (PBO). The comparison of these various real-time solutions allows a realistic evaluation of day-to-day software performance especially when faced with adverse conditions such as data gaps or poor satellite geometry. Forward models for scenario earthquakes in this region are used to "fingerprint" the coseismic displacements expected from various offshore events which allows an evaluation of the effectiveness of the current regional coverage. The present distribution and density of real-time sites is largely sufficient for aiding the timely estimation of size, location, and nature of a great (M>8) megathrust earthquake. However, current coverage is inadequate for the unambiguous identification of the same parameters for 7<M<8 earthquakes, especially those occurring offshore northern Vancouver Island.