Southern Thailand's Seismicity and Crustal Deformation: Relations to Regional Neotectonics

Following the 2004 Sumatra-Andaman earthquake (M 9.1), local earthquake occurrences in Southern Thailand has been actively observed to gain insight into their spatial distribution and magnitude variation. This is particularly important in relation to two major fault zones that have been reactivated, the Khlong Marui and Ranong Fault Zones, which were previously thought to be dormant. As many as 221 local earthquakes that occurred between 2005 and 2020 were gathered for this study using the observations on local, national, and international networks. Using SEISAN software, digital seismograms of 174 local events captured by at least three local seismic stations were analyzed. The results of this study show that the local earthquake epicenters are scattered spatially in some onshore areas of Southern Thailand and offshore throughout the Andaman Sea and Gulf of Thailand. Majority of the local earthquakes occured within and adjacent areas of the two main fault zones, hence the main sources of local seismicity. Nearly all of the events at hypocenters, which have depths ranging from 1.0 km to 78.4 km, are classified as shallow earthquakes. In terms of magnitude, the range of moment magnitude values is -0.1 ≤ Mw ≤ 5.0. This study was complemented by GPS data to observe the crustal deformation in the region. This study also shows that Southern Thailand's seismicity and crustal deformation were significantly impacted by a number of significant regional earthquakes. This study might leads to a re-evaluation of the seismic hazards for Southern Thailand.