Continental Drift

[IGerstein]

Has continental drift been directly measured between continents, say, by interferometry or laser reflection off the moon? (I realize the forces driving continental drift produce local motions from earthquakes, but that’s not what I’m asking about.)

[Shiva]

Yup. Here’s an interesting site: http://www.unavco.ucar.edu/community/brochure/

Three basic approaches were attempted. Each faced formidable technical challenges - and all succeeded. Very Long Baseline Interferometry uses the difference in the time when radio signals from distant quasars arrive at different points on earth. Satellite Laser Ranging uses the time required by light from ground-based lasers to bounce off satellites. The third approach relies on the travel time of radio signals between satellites and ground stations. The most popular, convenient, and least costly of such measurements are made using the NAVSTAR satellites of the Global Positioning System (GPS).

[Triskadecamus]

There are also measurements of the motion of the two plates which meet at the San Andreas fault. Although those plates are not on separate continents, the principle is the same. There are some cool tunnels and such with laser survey equipment in them that measure distances across the fault in real time.

Tris