[J05-4] Crustal dynamics: Multidisciplinary approach to seismogenesis IV

[J05-4-05] Performance of VADASE single-frequency GPS solutions in the 2016 M 6.5 Meinong, Taiwan, earthquake

^○Ruey-Juin Rau¹, Choon-Muar Ker¹, Giorgio Savastano², Mattia Crespi² (1.National Cheng Kung University, Tainan, Taiwan, 2.University of Rome “La Sapienza", Rome, Italy)

The 6 February 2016 MW 6.5 Meinong earthquake produced widespread strong shaking with 30-85 cm/s Peak Ground Velocity (PGV) in the 30-km-away Tainan city, where we installed eight 1-Hz single-frequency (SF) and one dual-frequency (DF) GPS stations about 4 month before the earthquake. The observed PGVs are significantly higher than the near-fault ground motion collected from moderate-sized earthquakes occurred worldwide and caused about 10 buildings collapsed and 117 death in the Tainan city. We processed the 1-Hz SF GPS data with both VADASE (Variometric Approach for Displacement Analysis Standalone Engine) and RTK positioning approaches. VADASE developed by the Sapienza University utilizes the broadcast orbits and the time differences of the high-rate carrier phase observations to acquire the receiver motions at centimeters accuracy level. The RTKLIB software (Tomoji Takasu) was used for RTK solutions which requires reference stations. The comparisons between VADASE and RTK solutions for all the 1-Hz SF GPS stations are in general consistent. We also compare the VADASE 1-Hz SF GPS solutions with the nearby 40 m away DF GPS stations. The differences between these two are about 3 mm/s and 5 mm/s for H and V component, respectively. Based on the seismological observations, the Meinong event has a strong directivity effect with the seismic waves propagating mainly toward the west to where our GPS stations are located. This effect can be clearly seen in most of the 1-Hz SF GPS solutions indicating 25-40 cm/s, EW-PGV, in contrast to 7-20 cm/s, NS-PGV. Two stations however, show significant large NS-PGV of 32-40 cm/s in comparison with the EW-PGV of 5-11 cm/s. These two stations are located near the E-W-trending Hsinhua fault, where the fault may act as a structural barrier which caused fault-normal motions observed. The use of the VADASE approach in the 1-Hz SF GPS for the 2016 Meinong earthquake clearly demonstrates the feasibility of SF GPS Seismology.