Photo/Illutration An information screen at JR Tokyo Station announces a delay in the Tokaido Shinkansen service due to an earthquake on Aug. 9. (Kotaro Ebara)

A magnitude-5.3 earthquake that jolted the Tokyo area on the evening of Aug. 9 was a separate seismic event from one the day before that was far more powerful and triggered warnings that a megaquake could strike Japan’s Pacific coastline any day now.

The epicenter of the latest temblor was in western Kanagawa Prefecture, which is far from the scary Nankai Trough, an ocean-floor trench that runs along the Pacific coast from the Tokai to Kyushu regions.

This area has a history of being struck by megaquakes at a rate of one every 100 to 200 years.

Roughly 24 hours after the magnitude-7.1 quake on Aug. 8 in Kyushu, the Japan Meteorological Agency issued its first megaquake advisory, covering 707 municipalities from Okinawa to Ibaraki prefectures.

KANAGAWA QUAKE

Given that the epicenter of the Kanagawa earthquake was outside of the assumed epicenter of the Nankai Trough temblor, experts doubted it was directly related to the Aug. 8 Hyuganada earthquake in Miyazaki Prefecture.

The JMA said the focus of the quake was about 10 kilometers deep.

Koshun Yamaoka, an emeritus professor of seismology at Nagoya University, said the temblor is believed to have occurred near the boundary between the land plate and the subducting Philippine Sea Plate.

The area is far from the Hyuganada Sea, and it is unlikely that the two quakes are related, Yamaoka added.

He knew of no confirmed instances in the past of an earthquake occurring in one location affecting another location across the Izu Peninsula, triggering another earthquake.

“The Kanto region is an earthquake-prone area to begin with, and it is quite possible that an earthquake of magnitude 5 could occur regardless of the earthquake on Aug. 8,” Yamaoka said.

He urged people to “be aware” that more earthquakes of the same magnitude could hit “and to respond calmly.”

Kenji Satake, an emeritus professor at the University of Tokyo, agreed that the Aug. 8 and 9 earthquakes were not directly related.

“It is far from the assumed epicenter of the Nankai Trough earthquake, and the distance from the Hyuganada Sea makes it difficult to consider a direct impact,” he said.

The Tokaido Shinkansen was suspended between Shinagawa and Shizuoka stations due to the Aug. 9 earthquake, but resumed operations at 9 p.m.

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