Mentawai Island has the highest tectonic activity in Indonesia because to its position inside the collision zone of the Indo-Australian plate and the Eurasian plate. Continuous plate movement can be a source of earthquakes. A result of plate tectonics is the alteration of coral reef regions. Nonetheless, we have not yet delineated the sites where coral reefs have experienced substantial alterations. This study seeks to delineate the alterations in coral reef areas in the Mentawai Islands subsequent to previous earthquake occurrences. This approach detects underwater objects and identifies alterations in coral reef regions. We utilized Envi and ArcGIS to analyze Landsat data from 2005, 2010, and 2021, detecting alterations in the coral reef area. According to the findings, the area of coral reefs underwent fluctuations, seeing both increases and decreases between 2005 to 2010 and from 2010 to 2021.