Combining Independent Geodetic Measurements for Studies of Vertical Crustal Motions in the British Isles

We introduce the British Isles as a prime laboratory for the combination of independent geodetic measurements in order to describe present-day secular vertical crustal motions. In contrast to North America or Fennoscandia, where the maximum vertical motion due to glacial isostatic adjustment is at the cm/yr level, the British Isles undergo motions of few mm/yr, placing tight constraints on any measurement techniques applied to reliably detect such small changes. Although, the GPS has been demonstrated as being a very useful tool for this purpose in North America or Fennoscandia, it remains a challenge to accurately determine the vertical crustal motions at the magnitudes expected for the British Isles, given the current limitations in the accuracies associated with the International Terrestrial Reference Frame (ITRF), the modelling of systematic biases in the processing of GPS measurements, and/or GPS processing strategies themselves. In this presentation we discuss present-day vertical crustal motions of the British Isles inferred from recent results from absolute gravity and GPS measurements and compare these with geological information and sea level records, and conclude that only a combination of these give a reliable picture of the vertical crustal movements observed in the British Isles.