Magnitude 4.8 Earthquake Near Asahi, Japan: Submarine Cable Anomalies Detected

What Happened

On November 3, 2026, at 07:40 local time, an earthquake of magnitude 4.8 struck 6 km south of the city of Asahi, Japan. The epicenter was located near the Pacific Ocean coastline, an area known for its dense network of submarine cables that play a critical role in global communications. This seismic event occurred in a region that serves as a vital hub for international connectivity, linking Japan with other Asian countries and North America. The proximity of the earthquake to the coastline raised concerns about potential impacts on submarine cable infrastructure, which is essential for maintaining uninterrupted internet and data services across continents.

Cables in Zone

Within a 500 km radius of the earthquake's epicenter, GeoCables identified several key submarine cables that are integral to international connectivity. These include:

• Candle: Spanning 8000 km, this cable is scheduled to be ready for service (RFS) in 2028, making it one of the newer additions to the region's infrastructure.
• Asia Submarine-cable Express (ASE)/Cahaya Malaysia: Operational since 2012, this 8148 km cable is a major route connecting Japan to Southeast Asia.
• Asia Direct Cable (ADC): Measuring 9988 km, this cable became operational in 2024 and is designed to handle high-capacity data traffic between Asia-Pacific regions.
• Southeast Asia-Japan Cable (SJC): With a length of 8900 km and operational since 2013, this cable facilitates connectivity between Japan and Southeast Asia.

The nearest cable landing stations to the epicenter are Maruyama (94.9 km) and Chikura (98.6 km), both critical nodes for the region's submarine cable network. Additionally, older cables such as Pacific Crossing-1 (PC-1, RFS 1999) and EAC-C2C (RFS 2002) are also located within the affected zone. These cables, while still operational, may be more vulnerable to seismic activity due to their age and design.

What Our Measurements Show

GeoCables' real-time monitoring systems detected significant anomalies in round-trip time (RTT) measurements across several submarine cables in the affected region. These anomalies are indicative of potential disruptions or stress on the cable routes or associated equipment. Key findings include:

• Candle RTT: Increased from 317.1 ms to 472.3 ms, marking a rise of 155.1 ms, which corresponds to 8.7σ above the norm.
• ASE RTT: Rose from 97.6 ms to 153.2 ms, an increase of 55.6 ms, or 2.9σ deviation.
• ADC RTT: Grew from 95.5 ms to 148.4 ms, showing an increase of 52.9 ms, equivalent to 2.2σ above standard levels.
• SJC RTT: Climbed from 77.3 ms to 149.8 ms, a significant rise of 72.5 ms, corresponding to 5.1σ deviation.

These RTT increases, measured in milliseconds, are critical indicators of potential issues such as cable stress, minor damage, or disruptions in signal transmission. GeoCables' systems consistently monitor these metrics to ensure network stability and performance.

Context and Risks

The region impacted by the earthquake is a strategic node for the global submarine cable network, facilitating high-speed data exchange between Asia, North America, and other parts of the world. Submarine cables in this area support major telecommunications operators, including NTT, PLDT, and China Telecom, and carry substantial volumes of international internet traffic. Any disruptions in this network could have cascading effects on global connectivity, affecting businesses, governments, and individuals reliant on seamless data transmission.

While anomalies in RTT measurements do not necessarily confirm physical damage, they highlight potential risks and warrant thorough investigation. The dense concentration of cables in this region underscores its importance, and GeoCables' proactive monitoring ensures that any issues are promptly identified and addressed.

Further Monitoring

GeoCables continues to closely monitor the submarine cable network in the earthquake-affected zone. Special attention is being given to the Candle, ASE, ADC, and SJC cables, as well as older infrastructure like PC-1 and EAC-C2C, which may be more susceptible to seismic impacts. Efforts are focused on stabilizing RTT metrics and analyzing potential changes in route topology or equipment performance. GeoCables' advanced monitoring systems ensure comprehensive oversight of the network, and updates will be provided as new data becomes available.