Vertical Displacements at SLR and GNSS Stations in the Pacific Region

The Satellite Laser Ranging stations at Monument Peak in S. California andArequipa in S. Peru are in earthquake zones. MONL is close to the San AndreasFault; AREL sits on the back-arc of the Nazca Plate. Position shifts are expected andseen at the co-located SLR and GNSS stations there at times of large earthquakes.Engineering changes made at the SLR stations are routinely calibrated. The heightof the optical axis of the ranging machine is closely monitored. The verticaldisplacements measured by the SLR and GNSS instruments are similar at times ofearthquake discontinuities. Post- and inter-seismic patterns in station heightobserved by the co-located systems are compared and common trends noted.Vertical trends at other Pacific stations are also seen and supported bymeasurements from alternative space techniques. The SGF SATAN SLR dataanalysis system provides a robust assessment of the long-term behaviour of thestation heights. The long history of SLR measurements and GNSS observationsshows significant deformation signals in the vertical component of the regionalreference frame. There is some evidence of a change in regional vertical behaviourin the early 2000s.