Comparisons of Long-term Trend of Crustal Strains and its Principal Axes Measured by Quartz Tube Extensometers and GNSS in Southwestern Miura Peninsula, Japan

Quantitative evaluation of long-term crustal strains is important to understand tectonic processes operating in the area of study. The measured strains by quartz tube extensometer in a designated observatory vault usually have high resolution, however, the data are known to contain other signals such as oceanic loading, earth tide, barometric pressure, and rainfall. Also, it is possibly affected by local heterogeneity of rock masses. On the other hand, GNSS (Global Navigation Satellite System) measurement has relatively low resolution but gives regionally averaged strain. GNSS measurement is affected by the temporal changes of the atmospheric conditions such as ZWD (Zenith Wet Delay). Therefore, it is not straightforward to compare the measured strain results obtained from the above mentioned approaches. Here, we analyzed datasets from a set of quartz tube extensometers in an observatory vault and a set of four GNSS receivers, and checked their consistency. The southwestern Miura peninsula, Japan, was selected for this study because we can obtain both data in the area. In our analysis, BAYTAP-G (Tamura et al., 1991) was applied to extract long-term trend components from original records of strains from 1997-2015. We found that the dates of folding points appeared in the long-term trends from both quartz tube extensometer and GNSS were consistent between each other. In addition, directions of maximum principal strain axis estimated from quartz tube extensometer datasets were found to be ranged from SSW to SE during measurement periods, while from SW to SSW from GNSS analysis. These results indicates that the measured strains by extensometers at an observatory vault in this area reflected larger scale strains measured by GNSS.