Abstract

All earthquakes over 5th magnitude since 1962 were recorded on Sumatra and surroundings, marking their depths and distinguished whether they were triggered by maximum westward or north-southward tidal torques. Greatest differences were found in period 2003-2009 where earthquakes triggered by north-southward torque were situated on rim of Sumatra continental area on Mentawai Fault. Period 2009-2023 is characteristic by large number of westward tidally triggered earthquakes, situated westward from Sumatra coast reaching sometimes as far as into oceanic lithosphere. As far as the great earthquake M 9.1, 26.12.2004 was triggered by the beat of close tidal frequencies: 19 years Metonic cycle and Moon’s nodal 18.61 years variations and if the beat were symmetric with maximum amplitude 26.12.2004, then because Full Moon will be 27.12.2023 and New Moon 11.1.2024, (Moon’ declinations large +28.1º and -27.6º respectively), the earthquake will occur of 6.5 5th magnitude as similar earthquake 27.12.1985. This prediction has not been fulfilled because the beat has not been symmetric, but asymmetrically shifted by westward tidal torque as proved by absolutely missing earthquakes 25. and 26.12. 2023, documented by very sensitive earthquakes detection up to 2.5 magnitude.