Magnitude 4.6 Earthquake Near Izu Islands Causes RTT Anomalies on Submarine Cables

Earthquake off the Izu Islands

On October 8, 2026, at 21:32:03 local time, an earthquake of magnitude 4.6 occurred in the area of the Izu Islands, Japan. The epicenter was located in the Pacific Ocean near several key points of submarine cable infrastructure. This event drew attention from telecommunications operators due to potential impacts on submarine cables passing through the region.

Submarine Cables in Earthquake Zone

Around 500 kilometers from the epicenter are several important submarine cables. Among them:

• APCN-2 (19,000 km, RFS 2001, operators: AT&T, BT) with a node in Chikura, Japan (475.6 km from the epicenter).
• EAC-C2C (36,500 km, RFS 2002, operator: Telstra) with a node in Chikura, Japan (475.6 km).
• Asia Submarine-cable Express (ASE) (8,148 km, RFS 2012, operators: NTT, PLDT) with a node in Maruyama, Japan (478.6 km).
• Asia Direct Cable (ADC) (9,988 km, RFS 2024, operators: China Telecom, China Unicom) with a node in Maruyama, Japan (478.6 km).
• Local cables such as 5 Villages 6 Islands and Hachijojima-Mainland serve nearby islands.

The most distant of the affected cables is Ogasawara Cable Network (1038 km, RFS 2011, operator: Tokyo Metropolitan Government), with a node in Chichijima, Japan (436.6 km from the epicenter).

What our measurements show

Monitoring RTT (round-trip time) revealed significant anomalies on several cables:

• On APCN-2, RTT increased from 94.3 ms to 280.3 ms (delta +186.0 ms, 41.8σ).
• On EAC-C2C, RTT rose from 84.8 ms to 221.8 ms (delta +137.0 ms, 11.7σ).
• On ASE, RTT changed from 89.2 ms to 183.2 ms (delta +94.0 ms, 2.4σ).
• On ADC, RTT increased from 107.6 ms to 212.4 ms (delta +104.8 ms, 5.3σ).

This data indicates temporary changes in route characteristics, likely related to seismic waves or ground displacement.

Context and risks

The Izu Islands region is an important node for submarine cables connecting Asia with the rest of the world. Anomalies in RTT may affect data transmission speed and connection stability, especially for traffic between Japan, Southeast Asia, and North America. If cable damage is confirmed, it may require significant efforts for repair, temporarily increasing load on alternative routes.

It is important to note that local cables such as 5 Villages 6 Islands and Hachijojima-Mainland did not show noticeable changes in characteristics, indicating their resilience to seismic impacts.

Further Monitoring

We will continue to monitor the condition of affected cables, paying special attention to APCN-2, EAC-C2C, ASE, and ADC. Additional RTT measurements and analysis of possible damage will be conducted in the coming days. We will also keep an eye on restoration efforts if needed and evaluate their impact on global internet traffic.

In addition, we plan to study how changes in traffic routing will affect delays and throughput in the region to provide a more complete picture of the consequences of this event.