Worldwide detection and classification of pre-eruptive tilt changes for understanding eruption mechanisms of volcanoes

Abstract Volcanic eruptions are sometimes preceded by tilt changes, which are indicators of eruption mechanisms and potential short-term precursors. Numerous studies have addressed the source mechanisms of individual tilt changes, but few have cataloged and compared tilt changes quantitatively across different volcanoes. In this study, we systematically surveyed tilt changes before eruptions across volcanoes worldwide that had a 1-min temporal resolution and were monitored by broadband seismometers or tiltmeters closer than 10 km from volcanoes. We identified 855 waveforms of tilt changes before 631 eruptions at ten volcanoes. We merged these newly identified pre-eruptive tilt changes with 3969 waveforms in Japan, which we previously identified, and classified them based on the similarity of waveforms. The results showed mixed contributions from various volcanoes to individual waveform groups. Acceleration followed by deceleration was the most frequent pattern, and the second most frequent was deceleration followed by acceleration; simple acceleration or deceleration was relatively rare, and no waveform groups showed linear tilt change. While acceleration occurred continuously, deceleration occurred abruptly during a tilt change. These features are the first discoveries of this study based on a comprehensive analysis of worldwide data and would facilitate our understanding of short-term (several-to-several tens of minutes) precursory processes before volcanic eruptions. Graphical Abstract