Magnitude analysis of aftershocks of the Mw 9.3 Sumatra-Andaman Earthquake recorded at the temporary PSU Seismic Station in Phang nga, Thailand

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.