Magnitude 6.9 Earthquake Near Pematangsiantar Causes RTT Anomalies on SJC2, APG Cables
What Happened
At 13:54:51 local time on August 15, 2026, an earthquake of magnitude 6.9 occurred 15 km northwest of the city of Pematangsiantar (Indonesia). The epicenter was at a depth characteristic of regional tectonic activity. This area is near key submarine cable routes connecting Southeast Asia with the rest of the world.
Cables in Zone
Within a radius of 500 km from the earthquake's epicenter, several submarine cables are located, including Southeast Asia-Japan Cable 2 (SJC2), Asia Pacific Gateway (APG), Lumut-Pangkor Island, SeaMeWe-6, MIST, India Asia Xpress (IAX), I-2SEA, and SAFE. Among them, the SJC2 cable exit point in Songkhla (Thailand) is the closest to the epicenter - 495.8 km away. The APG cable has an exit point in Cherating (Malaysia) at a distance of 499 km. Other cables are located further away; for example, SeaMeWe-6, MIST, and IAX pass through Mori (268.8 km from the epicenter).
What Our Measurements Show
Our monitoring systems have detected significant anomalies in signal delays (RTT) on two cables within the affected area. On SJC2, the base RTT was 71.0 ms but increased to 181.5 ms after the event (delta +110.5 ms, corresponding to 11.4σ from the base value). On APG, the base RTT increased from 75.1 ms to 146.9 ms (delta +71.8 ms, 6.2σ from normal). These deviations indicate possible changes in cable characteristics such as shifting or damage to individual segments. Despite their proximity to the epicenter, cables Lumut-Pangkor Island, SeaMeWe-6, MIST, IAX, and others have shown stable parameters, indicating their resilience.
Context and Risks
Southeast Asia is a key node for global internet traffic, with cables such as SJC2 and APG providing critical connections between Asia, America, and Europe. An increase in RTT on these cables may lead to increased data transmission delays and rerouting of traffic onto alternative routes, creating additional load on other channels. In the event of confirmed physical damage to the cables, repair may be required, which could extend the time needed for normal operation to resume.
Further Monitoring
We continue to monitor the condition of all submarine cables in the earthquake-affected zone. Special attention is being paid to SJC2 and APG, where significant anomalies in RTT have been recorded. Additional analyses will be conducted to determine any possible damages. It is also important to assess the impact on other cables such as SeaMeWe-6 and MIST, which play a crucial role in maintaining regional connectivity. We will provide timely updates on any changes in the infrastructure status.
