Indonesia Cable-Based Tsunameter (InaCBT): Tsunami detection and identification on other seismic wave signals

The Indonesian Cable-Based Tsunameter (InaCBT) is the most recently developed innovative prototype that has been deployed in the Flores Sea north of Labuan Bajo, Flores Island, Indonesia. Two ocean bottom units (OBU) were attached to a single fiber-optic cable. The first one is 34.0 km from the shore at a depth of 2100 m (LB-01) and the second one is 54.2 km from the shore at depth of 4110 m (LB-02), respectively. Each OBU comprises one deepsea bottom pressure recorder (BPR); a three-axis accelerometer; and temperature, humidity, and leakage sensors. Since deployment, the InaCBT has detected at least three near-field and distant earthquake events. One of them, the M7.5 Banda earthquake (EQ), detected on January 9, 2023, resulted a rise of the sea level recorded at six coastal tidal stations around the location. Near real-time analysis applies Lanczos filtering to split EQ signals (high frequency) and tsunamis (low frequency, if present). EQ wave signals dominate at 10-14-second wave periods. Using data from Banda EQ, the low-frequency wave shows an oscillation that probably indicates the presence of a tsunami wave. The identification and distinction of EQs and tsunami can be done by directly filtering raw data without detiding and by using harmonic analysis. The 30-50-second cut-off period can separate EQ and tsunami signals.