The largest aftershock (M 7.1) occurred on January 7, 10 days after the main shock near the coast in northern Iwate Prefecture. Seismic intensity 5 in JMA scale was observed in Hachinohe, and the aftershock caused numerous injuries and collapsed houses. There was considerable aftershock activity, with the largest aftershock occurring on January 7. The frequency of aftershocks gradually decreased thereafter (Fig.4-27, Fig.4-28).
Observations of the crustal movement using the Global Positioning System (GPS) detected movement of several centimeters to the east in all areas from Hokkaido to Tohoku accompanying the occurrence of the Earthquake far off the Coast of Sanriku.
The source region of this earthquake partially overlapped that of the 1968 Earthquake off the Coast of Tokachi, east off Aomori prefecture (M 7.9). This underscores the importance of studying the recurrence time of interplate earthquakes.