I don’t have a view into the primary sources, but this sounds like “four inches” as it would be measured at the surface of the globe by the angle subtended by the difference in the earth’s rotational axis as compared before and after the quake. Not a lot, and a one-time event rather than part of a cumulative trend. The coasts of America and Europe are moving apart more than that every year.
Correct, but not a huge issue the earth rotational's axis as defined by the inertial terrestrial reference frame drifts a small amount every year relative to the celestial inertial reference frame.We are currently using ITRF 2007 the ITFR07 is tied to the ICFR using VLBI observations from extra galactic pulsars. What has shifted is earth rotational axis as seen from the celestial frame, this displacement when plotted from the previous axis geoid intercept point has a displacement of 10". The reason for this shift is as the earths plates moved relative to each other the mass distribution of the plates shifted thus shifting the earths total center of mass and this shift is why the axis of rotation moved relative to the fixed celestial inertial frame. GPS can detect this shift as the GPS birds fly in celestial inertial space and when the earth shifts below them the CORS stations detect the shift in positions. Every CORS station is tied to ITFR00 and has its plate velocity vectors factored into the solution provided to geoinfomatic users such as myself.