An updated NAD83(CSRS) v7.1 velocity field and hybrid crustal velocity model for Canada

NAD83(CSRS) is the adopted 3D reference frame used for the Canadian Spatial Reference System (CSRS) and is defined by a transformation from ITRF. The reference frame is realized using a network of relatively sparse national and provincial active control stations and repeated high accuracy campaign surveys, as well as continuously operating stations in Greenland and bordering areas of the U.S. More recent realizations of NAD83(CSRS) include a GNSS-based crustal velocity model used to propagate coordinates to different reference epochs, and to support scientific studies such as natural hazards, earthquakes, and sea level rise. NAD83(CSRS) v7 is a new realization based on ITRF2014 that was released in early 2019. It includes a hybrid velocity model for the vertical component which integrates glacial isostatic adjustment (GIA) models with the GNSS-derived velocity field. This is particularly important in northern and remote regions where the NAD83(CSRS) network is sparse, but where vertical motions are strongly affected by GIA following the retreat of the Laurentian Ice Sheet, and/or by elastic rebound due to present-day ice mass change.

Since the release of NAD83(CSRS) v7, a new v7.1 velocity field has been produced. In addition to one more year of data at existing sites, it includes new sites in areas where GIA models are relatively poorly constrained. We describe the differences between the v7 and v7.1 velocity fields, and compare v7.1 velocities to more recent GIA and elastic rebound models. A new hybrid vertical velocity model has also been developed which integrates the new velocity field with the GIA model providing the best fit to the velocity field in critical areas.