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After the Mw 9.3 Sumatra-Andaman Earthquake on 26 December 2004, a temporary broadband seismic station was set up at the Khao Chang Telecommunication Station in Phang nga Province, Southern Thailand, in order to monitor aftershocks in an area bounded by 0o-20o N, and 90o-100o E. Altogether 98 events were identified during the study period from 1st to 12th January 2005; but six of these events are not listed in the catalog of the United States Geological Survey (USGS/ NEIC). Body wave magnitudes (mb) and moment magnitudes (Mw) of the events were determined and compared with USGS magnitudes. For mb, the PSU values are 0.215 higher than the USGS values, whereas for Mw, the PSU values are 0.268 lower than the USGS values. Differences in mb may result from differences in time windows chosen for the maximum amplitude determination, or from accuracy of the Q-value. Differences in Mw may result from assumptions made on velocity, attenuation and determination of the low-frequency part of the seismic spectrum. However, these differences are comparatively small considering that the USGS data are network values whereas the PSU data are from a single station.

Residual gravity anomaly with a minimum of about -140 mm s-2 with approximately NS trend and a limited axial length was observed over Hat Yai Basin in Peninsular Thailand. The modeled Hat Yai basin is about 1 km deep at its deepest, 60 km long and 20 km wide. The porosity of basin sediment and the amount of potential ground water reserves within the basin are estimated to be 39% and 121.7±0.8 km3 respectively, assuming full saturation. Within the topmost 80 m of ground where the present extraction is concentrated, the estimated ground water reserve is 12.5±0.5 km3.

Seismic refraction is a conventional geophysical method for determining geological structures by making use of velocity differences of propagating waves in various rock types. Data interpretation to determine the structures are based on travel time and distance from the source to each receiver (geophone) presented in the form of a t-x graph. In addition to the many conventional methods, our paper evaluates here a Genetic Algorithm (GA) for the interpretation of seismic refraction data. The studied subsurface structures were 2-layer and 3-layer models with horizontal and dipping planar interfaces. Actual field tests were also used for the evaluation. Comparing the GA interpretation technique with the conventional Seismic Interpretation Program (SIP), the results showed that the GA can process seismic refraction data well and gives virtually exact solutions for the synthetic structures. On actual field data, the results are quite similar to those from SIP.

After the Mw 9.3 Sumatra-Andaman Earthquake on 26 December 2004, a temporary broadband seismic station was set up at the Khao Chang Telecommunication Station in Phang nga Province, Southern Thailand, in order to monitor aftershocks in an area bounded by 0°-20° N, and 90°-100° E. Altogether 98 events were identified during the study period from 1st to 12th January 2005; but six of these events are not listed in the catalog of the United States Geological Survey (USGS/ NEIC). Body wave magnitudes (mb) and moment magnitudes (Mw) of the events were determined and compared with USGS magnitudes. For mb, the PSU values are 0.215 higher than the USGS values, whereas for Mw, the PSU values are 0.268 lower than the USGS values. Differences in mb may result from differences in time windows chosen for the maximum amplitude determination, or from accuracy of the Q-value. Differences in Mw may result from assumptions made on velocity, attenuation and determination of the low-frequency part of the seismic spectrum. However, these differences are comparatively small considering that the USGS data are network values whereas the PSU data are from a single station. [ABSTRACT FROM AUTHOR]