The 1998 Ryukyu Islands earthquake(石垣島南方沖地震,Ishigakijima nanpō-oki jishin?) occurred on May 4, 1998 at 08:30 local time (UTC+9) (on May 3 at 23:30 UTC) in the Philippine Sea region with Mw 7.5 (USGS) and M7.7 (JMA). The epicenter was 260 km (162 mi) from Ishigaki Island, Japan, 400 km (249 mi) from Basco, Philippines, and 425 km (264 mi) from Hualian, Taiwan. A small local tsunami of 4 cm (2 in) was observed on Miyako[disambiguation needed]. The earthquake was felt in the Ryukyu Islands and in parts of eastern Taiwan. The highest intensity was shindo 3 recorded on Yonaguni, Ishigaki, and Miyako. In 1999, the former Japan Marine Science and Technology Center (海洋科学技術センター) (Japan Agency for Marine-Earth Science and Technology (JAMSTEC) (海洋研究開発機構) after 2004) conducted an investigation in the region of the source of this earthquake.
The source of this earthquake was a sinistral (left-lateral) strike-slip fault. It was an intra-plate earthquake inside the Philippine Sea Plate. Such large intra-plate earthquakes inside the Philippine Sea Plate are not very common in this region. This earthquake was the strongest intra-plate earthquake inside the Philippine Sea Plate in the Ryukyu Islands region in 100 years as it occurred.