Relative deformation rates of collocated VLBI stations and comparisons with global solutions

Based on the 3-dimensional velocity vectors of VLBI stations in the international terrestrial reference frame ITRF2000 and the earth's plate movement model NNR-NUVEL-1A and taking as constraints the observed rates of change of VLBI baseline lengths, we have estimated and discussed the local/regional crustal relative deformation between the stations in 6 collocated VLBI sites world-wide, and made comparisons with the VLBI global solution glb2003 and the result of VTRF2003. Our results indicate that between the collocated VLBI stations Kashima and Kashima34 of Japan and between the NRAO20 and NRAO85_3 stations of Unites States there probably exists a relative vertical deformation of ∼4mm/yr, that a ∼2 mm/yr difference between the vertical deformation rates of the Westford and Haystack stations is basically confirmed, and that there exists a relative vertical deformation rate of 1∼ mm/yr between the Kokee and Kauai stations. Our method seems to be effective for detecting local/regional crustal vertical deformation between collocated VLBI stations and for improving the ITRF solution.