A VLBA survey of the core shift effect in AGN jets - I. Evidence of dominating synchrotron opacity K. V. Sokolovsky, Y. Y. Kovalev, A. B. Pushkarev and A. P. Lobanov A&A, 532 (2011) A38 Published online: 19 July 2011 DOI: 10.1051/0004-6361/201016072