Abstract
Abstract The displacement of the SAMP GPS station located in Medan City, Indonesia, is analyzed by means of an on-line point positioning method, the Canadian Spatial Reference System-Precise Point Positioning (CSRS-PPP). Based on the comparison of the results obtained with those from previous studies, we propose that CSRS-PPP can be applied to analyses of the displacement of a GPS station. Previous studies have focused solely on the “Sumatra-Andaman Islands Earthquake of December 26, 2004”; in contrast, we provide here an in-depth analysis of the crustal movements at the SAMP station for an expanded period of 2.5 years. CSRS-PPP, an Internet data processing service of the Department of Natural Resources Canada (NRCan), was used to process the data obtained at the SAMP station from January 2004 to July 2006. The data show a clear displacement in the southwestern direction from December 26, 2004 to March 28, 2005 when two major earthquakes occurred. However, after the midpoint of 2005, the data show displacement at a regular speed. In particular, the “Sumatra-Andaman Islands Earthquake (M w = 9.0) of December 26, 2004” led to a displacement of 0.1387 m (dn = −0.0122 m, de = −0.1382 m) to the southwest. The earthquake (M w = 8.7) that occurred on March 28, 2005 led to a displacement of 0.1921 m (dn = −0.1400 m, de = −0.1315 m) to the southwest. Starting from December 26, 2004, displacement to the southwest continued. From April 2005, however, the speed of the displacement gradually slowed down. The dn variation shows a displacement at a regular rate (−55.69 mm/year) from April 28, 2005 to July 2006, while the de variation shows a displacement at a regular rate (−23.66 mm/year) from July 5, 2005 to July 2006.
Highlights
On average, about 1000 earthquakes with intensities of5.0 or greater are recorded each year
Based on the comparison of the results obtained with those from previous studies, we propose that CSRS-PPP provides improved positions in the NAD83 (CSRS)-PPP can be applied to analyses of the displacement of a GPS station
The aim of this study was to process the GPS data of the SAMP GPS permanent station located in Medan City, Indonesia, from January 2004 to July 2006 and to analyze the result of displacement before and after the earthquakes of the same period
Summary
About 1000 earthquakes with intensities of5.0 or greater are recorded each year. Only an average of one per year is classified as a great earthquake (intensity ≥ 8.0), major earthquakes (intensity 7.0–7.9) occurring 18 times a year on average, strong earthquakes (intensity 6.0–6.9) occurring ten times a month, and moderate earthquakes (intensity 5.0–5.9) occurring more than twice a day (Bolt, 1993; Lomnitz, 1994). Because most of these earthquakes occur under the ocean or in underpopulated areas, they pass unnoticed by all but seismologists. Data from these GPS stations are transferred to the GPS analysis centers of the International GNSS service (IGS) for analysis and management (Beutler et al, 1995a)
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