We began Distributed Acoustic Sensing (DAS) observations along the optical fiber cables running along the Midorikawa River in Kumamoto Prefecture on August 21, 2026.
DAS is an observation technique that uses optical fiber cables themselves as sensors to acquire vibration data at intervals of several meters along cables extending for several tens of kilometers. Compared with conventional seismic observations, DAS provides exceptionally dense spatial sampling of seismic data.
Our center previously conducted DAS observations at the same location from February to March this year. The optical fiber cables are installed along the Midorikawa and Mifune Rivers and cross the Hinagu Fault along their route. Following the occurrence of the 2026 Kumamoto Earthquake, we resumed temporary observations at the site. The earthquake is considered to have involved rupture of the Hinagu Fault, and the optical fiber cable crosses directly over the fault.
DAS observations using an optical fiber cable crossing a fault before and after an M7-class earthquake are extremely rare worldwide.
In addition to capturing the ongoing aftershock activity in detail, we hope that comparison with the measurements conducted before the earthquake will allow us to detect changes in the heterogeneous structure of the fault zone caused by the 2026 Kumamoto Earthquake.
We would like to thank everyone at the Kumamoto River and National Highway Office and the Midorikawa Lower Reaches Branch Office of the Kyushu Regional Development Bureau, Ministry of Land, Infrastructure, Transport and Tourism, for their cooperation in conducting these observations.
