Magnitude 4.7 earthquake near Asahi disrupts submarine cable operations in Japan

Earthquake near Asahi

On October 28, 2026, at 20:32 local time, an earthquake of magnitude 4.7 occurred 6 kilometers north of the city of Asahi, Japan. The epicenter was located in close proximity to the coast, making this event significant for the region's submarine telecommunications infrastructure.

Cables in the affected area

Within a radius of 500 km from the epicenter, several key submarine cables are situated, including EAC-C2C (36500 km, RFS 2002, operator Telstra), Trans-Pacific Express (TPE) Cable System (17968 km, RFS 2008, operators AT&T, China Telecom), and New Cross Pacific (NCP) Cable System (13618 km, RFS 2018, operators China Mobile, China Telecom). The nearest cable exit points are in Ajigaura (67.6 km from the epicenter), Maruyama (105.1 km), and Wada (100.2 km).

Other cables in the zone include Pacific Crossing-1 (PC-1), Tata TGN-Pacific, FLAG North Asia Loop/REACH North Asia Loop, and Asia United Gateway East (AUG East), but anomalies have been detected only on the first three systems as of now.

What our measurements show

Monitoring has shown significant changes in signal transit time (RTT) on three cables:

• EAC-C2C: RTT increased from 88.7 ms to 181.9 ms (an increase of 93.2 ms, which is equivalent to 24.4 standard deviations from the baseline).
• Trans-Pacific Express (TPE): RTT rose from 166.7 ms to 315.5 ms (an increase of 148.8 ms, or 411.1 standard deviations).
• New Cross Pacific (NCP): RTT increased from 101.7 ms to 245.6 ms (an increase of 143.9 ms, which is 2.7 standard deviations).

These data indicate possible damages or temporary failures in the operation of submarine cables.

Context and Risks

The Japanese coastline is a crucial node for submarine cables connecting Asia with North America and other regions. Anomalies in cable operations, such as TPE and NCP, can lead to increased data transmission delays between continents, which is particularly critical for financial markets, cloud services, and other high-speed applications. An increase in RTT by tens of milliseconds can significantly impact the quality of service provided by telecom operators.

Moreover, cable damage in this region may require complex and costly repair work, considering the depth and complexity of the seabed terrain.

Further Monitoring

We will continue to monitor changes in the operation of submarine cables in the earthquake-affected zone. Special attention will be paid to the stability of RTT on EAC-C2C, TPE, and NCP, as well as potential changes on other cables such as PC-1 and Tata TGN-Pacific. If necessary, we will also monitor repair work and assess its impact on capacity recovery.

Additional data and updates on the situation will be published on the relevant cable and location pages on GeoCables.com.