Simultaneous observations of short-period (<1 hour) mesospheric gravity waves were made over an extended base-line (~660 km) from two sites in Japan (at Shigaraki and Yamagawa) during the SEEK (Sporadic-E Experiment over Kyushu) campaign, 9--23 August, 1996. Coincident image data obtained on four nights provided a rare opportunity to investigate the horizontal spatial extent and propagation characteristics of the waves in detail. Surprisingly, out of a total of 12 events observed from Shigaraki and 10 from Yamagawa at most only three exhibited similar propagation characteristics at each site. The majority of the wave displays (~70--75%) had quite dissimilar characteristics suggesting a preponderance for localized wave motions of limited lifetimes and geographical extent. A marked preference for wave progression towards the N-NE indicates that the gravity waves imaged in the near infrared OH and OI(557.7 nm) nightglow emissions were probably not directly associated with the observed E-region irregularities. ¿ 1998 American Geophysical Union