Magnitude 7.4 Earthquake Strikes Near Philippines, Japan Issues Tsunami Advisory for Slight Sea-Level Changes

At approximately 10:44 AM Japan time on October 10, a powerful magnitude 7.4 earthquake struck with its epicenter near the Philippines. Following this earthquake, the Japan Meteorological Agency (JMA) issued a "Tsunami Forecast (slight sea-level changes)" for the Japanese coast, although no damage from a tsunami is expected.

The epicenter was located near Mindanao in the Philippine Islands, with the depth estimated by some sources to be 58.1 km. For an earthquake of this magnitude, the Pacific Tsunami Warning Center (PTWC) issued warnings, indicating the possibility of a 1-3 meter tsunami for the Philippine coast and 0.3-1 meter for Indonesia and Palau. Residents in these areas are urged to remain vigilant.

In Japan, slight sea-level changes (less than 0.2 meters) are anticipated across a wide range of coastal areas, including Miyagi Prefecture, Sagami Bay, and the Uwa Sea coast in Ehime Prefecture. Consequently, people near the coast are advised to pay attention to waves as a precaution. Especially along the Miyagi coast, a high wave advisory has already been issued due to the effects of Typhoon No. 22, necessitating vigilance against high waves accompanied by swells.

The JMA continues to urge the public to check the latest information, even though no tsunami damage is expected. Notably, prior to this event, a magnitude 7.0 earthquake also occurred near the Philippines (Leyte) on September 30, drawing attention to seismic activity in this region.

The Context

Both the Philippines and Japan are situated along the Pacific Ring of Fire, a horseshoe-shaped belt around the Pacific Ocean characterized by frequent earthquakes and volcanic eruptions. This geographical feature means that significant seismic activity in one part of the region can generate tsunamis that propagate across the ocean, potentially affecting distant coastlines.

Japan's "Tsunami Forecast (slight sea-level changes)" is the lowest level of its tsunami warning system, indicating that sea-level changes are expected to be less than 0.2 meters and are not anticipated to cause damage. This differs from a "Tsunami Advisory" (0.2-1 meter waves) or a "Tsunami Warning" (1 meter or higher waves), which would prompt stronger safety measures, including evacuation. The depth of the earthquake (58.1 km) is moderately deep; deeper earthquakes tend to generate less destructive tsunamis than very shallow ones, but can still cause significant sea-level disturbances.

The mention of Typhoon No. 22 affecting Miyagi Prefecture is crucial. Strong winds and swells generated by a typhoon can exacerbate the dangers along the coast, potentially making even slight tsunami-related sea-level changes more hazardous, especially if they coincide with high tide or existing rough seas.

The previous M7.0 earthquake near Leyte on September 30 indicates a period of heightened seismic activity in the Philippine region, which is a common occurrence given its location on a major tectonic plate boundary.