The occurred on May 4, 1998 at 08:30 local time (UTC+9) (on May 3 at 23:30 UTC) in the Philippine Sea

Philippine Sea

The Philippine Sea is a marginal sea east and north of the Philippines occupying an estimated surface area of 2 million mi² on the western part of the North Pacific Ocean...

 region with M_w 7.5 (USGS) and M7.7 (JMA). The epicenter was 260 km from Ishigaki Island, Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

, 400 km from Basco

Basco

-Places:Philippines*Basco, Batanes, a municipality in the PhilippinesUnited States*Basco, Illinois, a village*Basco, Wisconsin, an unincorporated community...

, Philippines

Philippines

The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

, and 425 km from Hualian

Hualian

Hualian may refer to:*Hualian City, a city located in Hualian County, Taiwan, Republic of China*Hualian County, a county located in eastern Taiwan, Republic of China*Beijing Hualian, a company based in Beijing, People's Republic of China...

, Taiwan

Taiwan

Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...

. A small local tsunami

Tsunami

A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake...

 of 4 cm was observed on Miyako

Miyako

-Places in Japan:*Miyako, Iwate, a city in Iwate Prefecture*The Miyako Islands, including Miyako Island itself**Miyakojima, Okinawa, a city of the Miyako Islands**Miyako language, the Ryukyuan dialect spoken on Miyako Island and other nearby islands...

. The earthquake was felt in the Ryukyu Islands

Ryukyu Islands

The , also known as the , is a chain of islands in the western Pacific, on the eastern limit of the East China Sea and to the southwest of the island of Kyushu in Japan. From about 1829 until the mid 20th century, they were alternately called Luchu, Loochoo, or Lewchew, akin to the Mandarin...

 and in parts of eastern Taiwan. The highest intensity was shindo 3

Japan Meteorological Agency seismic intensity scale

The Japan Meteorological Agency seismic intensity scale is a seismic scale used in Japan and Taiwan to measure the intensity of earthquakes. It is measured in units of...

 recorded on Yonaguni

Yonaguni

is one of the Yaeyama Islands. It is the westernmost inhabited island of Japan and lies from the east coast of Taiwan, between the East China Sea and the Pacific Ocean proper....

, 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 inner-plate earthquake inside the Philippine Sea Plate. Such large inner-plate earthquakes inside the Philippine Sea Plate are not very common in this region. This earthquake was the strongest inner-plate earthquake inside the Philippine Sea Plate in the Ryukyu Islands region in 100 years as it occurred.