SEISMICITY OF CENTRAL NORTHERN THAILAND FROM 1999-2010 SEISMIC DATA OF THE KAENG SUA TEN SEISMOGRAPHIC NETWORK

This thesis studies the characteristics of present-day earthquakes in northern Thailand from instrumental data recorded at the Kaeng Sua Ten seismographic network, Royal Irrigation Department, by relocating the earthquake location from event primary and secondary waves arriving times and the Triangulation method, from origin time of 128 earthquakes during the year 1999 to 2010. The result of this study confirms that the earthquakes in the study area consist of small earthquake less than 4.9 on Richter magnitude scale and are shallow earthquakes with depth ranges from 0-61 kilometer. The earthquakes mostly have the magnitudes of 3-4.9. When considering those within 50 kilometers of the network center, it is found that the distribution of the earthquakes location is clearly and significantly associated with the fault zones of northern Thailand. However, some of the smaller than magnitude 3 and shallower than 10 kilometers which can be considered to be the back-ground earthquake did not relate to any lineament on the ground surface. The study also can be concluded that the highest seismic risk area is covered by latitude 18.75o-19.75o N and longitude 98.75o-99.75o E, based on Gutenberg-Richter relationship where the b-value is 0.59 which is smaller than the previously reported. The newly located epicenter of the Kaeng Sua Ten seismographic network’s when compared to the previously located data and with those of Thai Meteorological Department are different both in the epicenter location and the magnitude. The newly located epicenters correlate better to the existing active fault locations.