Many ground deformations have been occurred by earthquakes and volcanic activities in Republic of the Philippines. The monitoring using InSAR, which is capable to observe a wide area, as well as GPS measurement and leveling survey, which are capable to measure land displacement less than centimeter, is actively conducted in this country. In the past studies, the ground deformation due to pumping of ground water and geothermal fluid, creep-slip of active fault in the southern segment of Valley Fault System, and the activity of Taal volcano were extracted by InSAR using JERS-1/SAR data. In this study, the authors report the creep displacement in the south part of Valley Fault System and land subsidence detected by InSAR using ENVISAT and PALSAR as well as by leveling survey. Leveling survey has been carried out on six lines crossing the West Valley Fault 2 to 4 times every year since 1999. Clear displacements were detected on four lines of them. The amount of average displacement was 0.6 to 1.4cm/year before 2004, while it was 2.0 to 4.2cm/year after 2004. This shows that the rate of displacement has been rapidly increasing by time.
As the results of InSAR processing using JERS-1/SAR data observed from 1993 to 1998, it was extracted a displacement which the east side of the West Valley Fault had moved down. The amount of the displacement was approximately 6 cm per 3.7 years. As the result of InSAR processing using ENVISAT data in 2003 also detected displacement in the same region which the east side of the fault was moving down (2 cm/280 days). The amount of displacement of the fault measured by InSAR was increasing with passing time from 1.6cm/year to 2.6cm/year. This was in accordance with the results of leveling survey.
Next, we performed detailed analysis on the temporal change of surface deformation by applying smoothness-constrained time series analysis using ABIC minimization method to the result of InSAR from ENVISAT data between March 2003 and January 2007. The analysis clearly showed uplift (1.5 cm/year) and subsidence (1.1 cm/year) on the west and east side of the West Valley Fault, respectively. In addition, a total of eight phase anomalies that indicate the large-scale ground subsidence caused by intensive use of groundwater were detected. The largest one was extracted in Valenzuela, north Manila, where the subsidence of 10.6 cm/year was measured. The results from InSAR using PALSAR data were fairly consistent with that using ENVISAT data, demonstrating the ground subsidence in the same locations. However, slow displacement occurring along the Valley Fault could not be detected due to the short operation period of PALSAR. We intend to determine the distribution of deformation around the Valley Fault in detail as more PALSAR data accumulate and become available in the future.