Magnitude 5.1 earthquake near Saipan impacts RTT on key regional submarine cables

Earthquake near Saipan

An earthquake of magnitude 5.1 occurred at 11:37 UTC on September 16, 2026, 172 km east-southeast of the city of Saipan, Northern Mariana Islands. This event was significant for the submarine telecommunications infrastructure in the region, given its proximity to important cable landing points on Guam and in the Northern Mariana Islands.

Cables in the affected area

Within a radius of 500 km from the epicenter, there are eight submarine cables:

• TPU (13470 km, RFS 2026, Google), exit point: Tanguisson Point, Guam (265.5 km from the epicenter).
• Guam Okinawa Kyushu Incheon (GOKI) (4244 km, RFS 2013, AT&T), exit point: Tumon Bay, Guam (268.0 km from the epicenter).
• HANTRU1 Cable System (2917 km, RFS 2010, FSMTCC, Hannon Armstrong), exit point: Piti, Guam (280.6 km from the epicenter).
• SEA-US (14500 km, RFS 2017, GTA TeleGuam, Globe Telecom), exit point: Piti, Guam (280.6 km from the epicenter).
• Mariana-Guam Cable (268 km, RFS 1997, PTI Pacifica), exit point: Rota, Northern Mariana Islands (206.6 km from the epicenter).
• Proa (2891 km, RFS 2026, Google), exit point: Tanguisson Point, Guam (265.5 km from the epicenter).
• Halaihai (17483 km, RFS 2027, Google), exit point: Tanguisson Point, Guam (265.5 km from the epicenter).
• Australia-Japan Cable (AJC) (12700 km, RFS 2001, AT&T, NTT), exit point: Tanguisson Point, Guam (265.5 km from the epicenter).

Metered anomalies

Monitoring showed a significant increase in round-trip time (RTT) on several cables:

• TPU: RTT increased from 104.8 ms to 256.2 ms (delta +151.4 ms, 2.9σ).
• GOKI: RTT increased from 58.3 ms to 247.4 ms (delta +189.2 ms, 14.8σ).
• HANTRU1: RTT changed from 210.5 ms to 297.5 ms (delta +86.9 ms, 2.9σ).
• SEA-US: RTT increased from 199.2 ms to 258.1 ms (delta +58.9 ms, 3.1σ).

Cables such as Mariana-Guam Cable, Proa, Halaihai, and AJC did not show significant deviations from baseline metrics, indicating the resilience of their infrastructure.

Impact on Internet Traffic

Anomalies in RTT on TPU, GOKI, HANTRU1, and SEA-US cables may lead to temporary data transmission delays, especially for users relying on these routes. The increase in RTT on GOKI, reaching 14.8σ, raises the most concern as it indicates significant impact on the cable. However, due to alternative routes via other cables such as Proa and Halaihai, global internet traffic in the region remains stable.

Plans for Further Monitoring

We will continue to monitor the condition of cables in this region, paying special attention to GOKI and TPU, where the most significant deviations have been recorded. Additional measurements will be conducted in the coming days to assess any potential damages and their impact on throughput. We will also keep an eye on the restoration of normal RTT parameters and the readiness of operators for repairs if necessary.