5:15 PM - 6:45 PM
[SGD02-P02] Attempts to Detect SSE in the Ryukyu Trench, South Ryukyu Block
Keywords:GNSS, GEONET
Slow earthquakes are non-seismic slip events that occur in the transition zone between stable and unstable slip on the plate boundary. Obara & Kato (2016) pointed out to occur in many parts of the world. Slow earthquakes, of which have long period variations with in the geodetical signal band are so called 'Slow Slip Events'. In Japan they often occur in the Japan Trench, Nankai Trough, and Ryukyu Trench. First, Heki & Kataoka (2008) reported the existence of the repeating SSEs in half annual year up to 2008 at the Ryukyu Trench using with GEONET stations with F3 solution. Next, Nishimura (2014) added the results up to the 2013. Ten years passed from the previous study, we can use more long-term records, but GSI stopped supply the F3 solutions in March 2022, have changed to F5 solutions. Thus, we should compare the F5 solution capability for SSE detection in the Ryukyu Trench from the past up to the future.
In this study, we attempted to detect SSE by conducting a long-term time-series variation analysis using time-series data of F3 and F5 solutions.For the analysis, we used the coordinates of F5 solution from April 1997 to August 2023 and F3 solutions from March 2022 in eight GEONET stations in the southern Ryukyu block, Yonaguni, Iriomote Island, Tarama, Ishigaki 1, Ishigaki 2, Hateruma Island, Irabu and Gusukube (0498). First, we performed offset cancellation by using offset correction data for F3 and F5 solutions published by geographical survey institute. Next, We calculated baseline in the geocentric coordinate system between Gusukube which can be regarded as a fixed point in the South Ryukyu Block (c.f.Heki&Kataoka.,2008) and each of the seven observation points. After that, we transformed the coordinates and obtained the variation in the direction of latitude and longitude. Then, from the east-west, north-south, north-south, and up-down components of the obtained baseline length variation, a fitting was performed to remove the linear trend associated with plate motion and the annual cycle associated with celestial motion and removed outlier by using 21-day moving median average. As with the Heki&Kataoka(2008),Nishimura(2014), we converted baseline to the plate motion in the subduction direction (N20W) in order to try to detect SSE.
In this presentation, we will report the results of SSE detection by F5 solution in the Ryukyu Trench and comparison between F3 and F5 solutions.
In this study, we attempted to detect SSE by conducting a long-term time-series variation analysis using time-series data of F3 and F5 solutions.For the analysis, we used the coordinates of F5 solution from April 1997 to August 2023 and F3 solutions from March 2022 in eight GEONET stations in the southern Ryukyu block, Yonaguni, Iriomote Island, Tarama, Ishigaki 1, Ishigaki 2, Hateruma Island, Irabu and Gusukube (0498). First, we performed offset cancellation by using offset correction data for F3 and F5 solutions published by geographical survey institute. Next, We calculated baseline in the geocentric coordinate system between Gusukube which can be regarded as a fixed point in the South Ryukyu Block (c.f.Heki&Kataoka.,2008) and each of the seven observation points. After that, we transformed the coordinates and obtained the variation in the direction of latitude and longitude. Then, from the east-west, north-south, north-south, and up-down components of the obtained baseline length variation, a fitting was performed to remove the linear trend associated with plate motion and the annual cycle associated with celestial motion and removed outlier by using 21-day moving median average. As with the Heki&Kataoka(2008),Nishimura(2014), we converted baseline to the plate motion in the subduction direction (N20W) in order to try to detect SSE.
In this presentation, we will report the results of SSE detection by F5 solution in the Ryukyu Trench and comparison between F3 and F5 solutions.