VLBI enabled a direct measurement of plate motions, which are the driving
forces of large earthquakes at plate boundaries.
The Earth's outer layer (crust and rigid upper mantle) is fragmented into a dozen or more plates that are moving relative to one another. Collisions and subductions of the plates lead to large earthquakes, volcanic eruptions, and other geophysical phenomena at plate boundaries. Japan's complex terrain and recurring earthquakes in the Tokai, Nankai, and Tonankai areas are the results of these plate motions.
Although plate motions were confirmed by geological and geomorphologic evidences, direct measurements of plate motions were difficult because they are small in quantity and global in scale. The emergence of space geodetic techniques such as VLBI made it possible for the first time to measure present-day plate motions. VLBI measurement results are utilized as the basis for Earthquake Research.
Japan-US VLBI observations have revealed that the Hawaiian Islands is approaching
to the Japanese Islands at a rate of 6 cm / year.
