We study the November 13, 1990 off-Primorskij earthquake, which occurred near the northern end of the Japan Sea off the coast of the Primorskij region, by using data from short-period and broad-band seismograph networks in Hokkaido, Japan. The main shock and four aftershocks are located from arrival times of P- and S-waves recorded by these networks. The main shock epicenter is located about 50 km off the coast at a depth of about 10 km, and the largest aftershock is located about 20 km southwest of the main shock. It is difficult to read the polarities of P-waves recorded by the short-period network; the source mechanism of the main shock is determined by moment tensor inversion of long-period wave-forms recorded by broad-band instruments. The source mechanism is characterized by a reverse faulting with a vertical T-axis and a horizontal P-axis trending in the WNW-ESE direction. We have examined earthquake data reported by the ISC and by the Academy of Sciences of the USSR to study previous seismicity in the vicinity of the November 13 earthquake; no significant well-located earthquake is reported in this region. The stress orientation in this region may have significant implications for the tectonics of the northern end of the Japan Sea, where a plate boundary between the Eurasian and North American plates has been proposed. ¿ American Geophysical Union 1992