Spatial Classification algorithm (Modified-ID3) to identify OLR anomaly preceding M≥6.0 earthquakes-A case study on the vicinity of the 26 December 2004 earthquake

The Megathrust 9.1M w earthquake in Sumatra – Andaman region on 26 December 2004 was the deadliest earthquake of the 21 st century. The study region comprises ten earthquakes that occurred within a 75-km radius of the 26 December 2004 earthquake from 1991 to 2021. To explore the spatial characteristics of the Outgoing Longwave Radiation (OLR) the grid comprising 11° × 11° was considered, which is roughly 15, 00,000 sq. km for a 12-month period before the earthquake, which is computed retrospectively by taking the event date as a base date. A novel “Modified-ID3” (M-ID3) is a spatial classification algorithm, applied to analyze the OLR flux spatially and it is categorized into two leagues, a) “Macro dimension League” (MaDL) and b) “Micro dimension League” (MiDL). The grid dimensions 11° × 11°, 9°×9°, and 7°×7° belong to MaDL, while MiDL grid dimensions are 5°×5° and 3°×3°. To compare the different grid dimensions, the OLR values of the grids are normalized. From the spatial analysis, the anomalous variations in MiDL were observed before 1 to 3 months prior to the occurrence of earthquakes. Also, it is found that the earthquakes have occurred when the OLR flux value crosses the critical value for both leagues and also, and the MiDL was found to be greater than MaDL. The pattern of OLR anomaly significantly differs spatially for prior and post scenario of 26 December 2004 earthquake. The OLR scenario for the recent past, the time period starting from 30-11-2020 to 30-11-2021 were analyzed and the observation of OLR anomalous flux is found at south-east region of study area. Hence, the authors inferred that the OLR could be considered a potential candidate as a precursor to identifying the probable location, magnitude, and time of impending earthquakes.