Earthquake Swarm Activity in the Tokara Islands (2025): Statistical Analysis Indicates Low Probability of Major Seismic Event

TL;DR

This study analyzes earthquake swarm data from the Tokara Islands in 2025, revealing that the seismic activity is likely magma-driven and not indicative of an imminent major tectonic earthquake, using statistical seismology methods.

Contribution

The paper applies exploratory data analysis to distinguish volcanic seismicity from tectonic activity, providing a statistical framework for hazard assessment in volcanic archipelagos.

Findings

2025 swarm resembles 2021 volcanic activity patterns

Low magnitude scale ({} = 0.37) indicates magma-driven seismicity

Exponential interval distribution ({} = 0.19 hours) supports magma activity hypothesis

Abstract

The Tokara Islands, a volcanic archipelago south of Japan's main islands, has experienced ongoing earthquake swarm activity in 2025, raising concerns about triggering the anticipated Nankai Trough earthquake. The Japan Meteorological Agency has dismissed this link, but the seismic activity's mechanisms remain unclear. This study uses Exploratory Data Analysis (EDA) to examine the 2025 swarm's statistical properties and compare them with historical patterns. The 2025 swarm's frequency and magnitude distributions closely resemble those of 2021 swarms, which coincided with volcanic activity at Suwanose Island, 10 km from the epicentral region, suggesting a magma-seismicity link. Statistical analysis shows a low magnitude scale ({\sigma} = 0.37) and moderate mean magnitude ({\mu} = 2.8), consistent with magma-driven seismicity, unlike the higher {\sigma} (1.2) and {\mu} (3.6) before the 2011 Tohoku earthquake. The exponential distribution of earthquake intervals ({\lambda} = 1/0.19 hours) further supports magma-induced activity. These findings indicate localized volcanic processes, not precursors to major tectonic events like the Nankai Trough earthquake. Statistical seismology effectively distinguishes volcanic from tectonic seismic processes for hazard assessment.