10:45 AM - 12:15 PM
[SGD02-P10] Long-term changes in continuous observation records of crustal strain at Imazu and Tsuruga in the northern part of the Kinki district, Japan
Keywords:Strainmeters, Long-term changes
Meteorological Research Institute installed borehole strainmeter and tiltmeter at Imazu and Tsuruga station in the northern part of the Kinki district, Japan and observations have been made since June, 1996. Imazu station is located near the Shiriuchi and Aibano faults in the Biwako West Coast fault zone and Tsuruga station is located near the Tsuruga fault in the Kohokusanchi fault zone. Looking at wider area, these stations are in the Niigata-Kobe Tectonic Zone (Sagiya et al., 2000) and attract attention from both the perspective of earthquakes and crustal deformation.
In this study, we investigated long-term strain changes recorded at these stations from June, 1996 to 2022. Strain steps caused by maintenance were removed from records in advance. Barometric pressure effects and tidal effects were corrected using Baytap-G software (Tamura et al. 1991). Coseismic steps at the 2011 Tohoku earthquake were also removed from data.
Seasonal strain changes are seen in the record of strainmeter at Imazu station and are correlated with water level in the borehole, which are estimated to be due to pumping up groundwater for melting snow near the station. Also, changes caused by environmental effect are seen in the ST-3 strain component at Tsuruga station. These strain changes were removed using the method of Yamamoto and Kobayashi (2009).
For borehole strainmeter fixed to the surrounding rock with the cement, change that is different from the crustal strain is prominent for several years after installation caused by change of temperature or pressure for the cement set. Change in this stabilization process was modeled by an exponential function, and the coefficients were calculated to minimize the residual with the strain data was minimized. For each component, a time constant of about several years was obtained, but in addition, a model that synthesizes an exponential function with a time constant of about several tens of days was more suitable for the stabilization process.
Figure shows strain records at Imazu and Tsuruga station after removing the seasonal changes and the stabilization changes. Change is appeared in each component from 2000 to 2005. Yamamoto and Kobayashi (2009) pointed out that this change may be due to long-term slow slip event in the Tokai district. Long-term slow slip event has also been detected in the Tokai district from 2013 to 2016, whereas, change in strain is not clear in the records of Imazu and Tsuruga.
In this study, we investigated long-term strain changes recorded at these stations from June, 1996 to 2022. Strain steps caused by maintenance were removed from records in advance. Barometric pressure effects and tidal effects were corrected using Baytap-G software (Tamura et al. 1991). Coseismic steps at the 2011 Tohoku earthquake were also removed from data.
Seasonal strain changes are seen in the record of strainmeter at Imazu station and are correlated with water level in the borehole, which are estimated to be due to pumping up groundwater for melting snow near the station. Also, changes caused by environmental effect are seen in the ST-3 strain component at Tsuruga station. These strain changes were removed using the method of Yamamoto and Kobayashi (2009).
For borehole strainmeter fixed to the surrounding rock with the cement, change that is different from the crustal strain is prominent for several years after installation caused by change of temperature or pressure for the cement set. Change in this stabilization process was modeled by an exponential function, and the coefficients were calculated to minimize the residual with the strain data was minimized. For each component, a time constant of about several years was obtained, but in addition, a model that synthesizes an exponential function with a time constant of about several tens of days was more suitable for the stabilization process.
Figure shows strain records at Imazu and Tsuruga station after removing the seasonal changes and the stabilization changes. Change is appeared in each component from 2000 to 2005. Yamamoto and Kobayashi (2009) pointed out that this change may be due to long-term slow slip event in the Tokai district. Long-term slow slip event has also been detected in the Tokai district from 2013 to 2016, whereas, change in strain is not clear in the records of Imazu and Tsuruga.