Optical Long Base Hydrostatic Tiltmeter for Slow Earthquake Detection

We present an optical long base hydrostatic tiltmeter (OLBT) designed to be able to detect slow earthquakes in this work. Interrogation is carried out by a high precision fiber-based Fabry-Perot interferometer that detects variations of the surface liquid level in a hydrostatic leveling vessel. Field results from a 41 m long OLBT installed along the Gulf of Corinth, Greece, near the Psathopyrgos fault since mid-February 2024 demonstrate a tilt resolution of 0.2 nanorad and a stability of better than 0.15 µrad per month. This can potentially enable the instrument to be employed for detecting and monitoring slow slip events over the long term in earthquake precursor research.