Earthquake Swarms in Japan: tokara Archipelago and Hokkaido Raise Concerns

The Tokara Archipelago, South of Kagoshima Prefecture, has experienced over 440 earthquakes in just five days. concurrently, hokkaido has recorded a seismic intensity of 4 six times in one month, heightening fears of a major earthquake. This article examines the potential damage from a massive earthquake and explores necessary preparations.

Tokara Islands: over 440 Earthquakes in 5 Days Cause islander Anxiety

Earthquakes persist near the Tokara Archipelago in Kagoshima Prefecture. From June 21st to 25th,there were six earthquakes with a seismic intensity of 4 or higher and over 440 earthquakes with a seismic intensity of 1 or higher.

On June 24th,Akuishi Island in the Tokara Archipelago experienced two earthquakes of magnitude 4.

According to Associate Professor imura Ryusuke at Kagoshima University, similar swarm earthquakes occurred in the same area in 2021 and 2023. In December 2021, an earthquake with a seismic intensity of 5 or higher led to the evacuation of 40% of the island’s residents. Over 300 earthquakes were observed that month.

The epicenter area lies within the “Tokara Gap,” a fault in a hollow region, where earthquake activity is frequent.

The Ryukyu Trench is East of the epicenter, where the Philippine Sea Plate subducts under the eurasian Plate. However, the current earthquake activity isn’t necessarily linked to this boundary.

Akuishi Island residents report sleep deprivation due to the constant shaking and express anxiety about a potential major earthquake.

Vice-Principal Kokubo of Akuishijima Academy described the situation as unsettling, with residents feeling trapped and uncertain about the future. Rumors linking the earthquakes to the eruption of Mt. Shinmoe-dake in Kagoshima have exacerbated concerns.

Associate Professor Imura clarified that the current swarm earthquake is unrelated to the Mt. Shinmoe eruption. He cautioned about the possibility of a magnitude 6 earthquake and emphasized the importance of earthquake planning, including securing furniture and providing mental care for children.

Hokkaido: Frequent Earthquakes Heighten fears of a Massive Earthquake

Hokkaido is also experiencing frequent earthquakes.

The Kuril Trench is formed by the Pacific Plate subducting under the North American Plate.

Several earthquakes with a seismic intensity of 4 have occurred along the Kuril Trench, with six recorded between May 15th and June 19th.

The probability of a massive earthquake occurring within 30 years in the Kuril Trench is significant. There’s approximately a 20% chance of an earthquake with a magnitude of 8.0 to 8.6 off Tokachi and about an 80% chance of an earthquake with a magnitude of about 7.8 to 8.5 off the coast of Nemuro.

Along the entire Kuril Trench, the probability of an earthquake with a magnitude above 8.8 is estimated at 7% to 40%.

Past super-massive earthquakes in Hokkaido occurred during the Early Edo Period (1611-1637), with an estimated magnitude of 8.8. A massive tsunami inundated up to 4 kilometers inland from the coastline.

This past earthquake was a trench-type earthquake, similar to the Great East Japan Earthquake.

Over the past 6,500 years, there have been 18 super-massive earthquakes along the Kuril Trench.

The average interval between these earthquakes is about 340 to 380 years. Approximately 400 years have passed since the last earthquake.

Assistant Professor Tomita Fumiaki of Tohoku University, who researches trench-type giant earthquakes, stated that while the situation is uncertain, the average interval between occurrences has passed since the 17th-century earthquake, suggesting a huge earthquake may be imminent.

Plate Abnormalities in the Kuril Trench: Evidence of Strain Accumulation

A seabed survey of the Kuril Trench is underway.

As 2019, research groups, including Tohoku University, have established GPS acoustic observation points on the seabed to investigate strain accumulation over five years.

The key to the inquiry is the movement of the seabed.

If the boundary between the north American Plate and the pacific Plate is loosely attached, only the Pacific Plate will sink, resulting in less strain and a lower likelihood of major earthquakes.

However, if the plates are tightly stuck, strain accumulates, increasing the possibility of a massive earthquake.

The latest survey results from March indicate that both plates move about 8 centimeters per year. This suggests the plates are firmly stuck, and strain continues to accumulate.

During the 17th century earthquake, the amount of plate shifted was estimated at 25 meters.

Currently, with a strain accumulation rate of 8 centimeters per year, a simple calculation over 400 years yields about 32 meters.

If the strain exceeds the limit, there is a possibility of a massive earthquake of around 8.8 magnitude, possibly triggering a major tsunami similar to the Great East Japan earthquake.

Disclaimer: This article provides information about recent earthquake activity in Japan. It is not intended to provide specific safety or preparedness advice. Consult with local authorities and experts for tailored guidance.

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