Abstract
The scattering model of incident seismic waves by an empty borehole has been presented to investigate the theoretical frequency response and the corresponding bandwidth of borehole tensor strainmeters. Inner-diameter changes of the stainless steel instrument casing are measured by horizontal extensometers (gauges), after the borehole tensor strainmeter is installed at a certain depth of the borehole and boned by expansive grout with the surrounding rock. There is, however, no answer for the difference between this case and the empty case. In this paper, the scattering model of incident elastic seismic waves by a two-ring borehole is introduced to investigate the influence of the expansive grout on theoretical bandwidth for the measurement of strain waves by borehole tensor strainmeters. The calculation of wave fields in the surrounding rock and the two rings by wave function expansion gives the inner-diameter changes of the stainless steel instrument casing. Several cases show that the mechanical parameters of the expansive grout have great influence on the frequency responses of borehole tensor strainmeters for different gauge combinations, but little influence on the bandwidth, which means that the high-frequency bandwidth promises the quantitative measurability of strain waves in the acoustical frequency range for borehole tensor strainmeters.
Highlights
IntroductionIn order to capture gentle tectonic strain caused by volcanic activity [1], fault failure process [2,3,4,5,6,7,8,9], etc., high-sensitivity borehole tensor strainmeters, such as RZB strainmeter [5], YRY strainmeter [10], and GTSM (Gladwin Tensor Strainmeter) strainmeter [11,12], have been developed and installed in Plate Boundary Observatory (PBO) [13,14,15,16,17] and the China Borehole Strainmeter Network [18,19]
Inner-diameter changes of the stainless steel instrument casing are measured by investigate the theoretical frequency response and the corresponding bandwidth of borehole tensor horizontal extensometers, after the borehole tensor strainmeter is installed at a certain depth of strainmeters [27]
A borehole of radius c = 65 mm, expansive grout layer of 11.5 mm thickness, and instrument casing of 2 mm thickness are taken as an example to discuss the frequency responses of borehole tensor strainmeters and corresponding bandwidth
Summary
In order to capture gentle tectonic strain caused by volcanic activity [1], fault failure process [2,3,4,5,6,7,8,9], etc., high-sensitivity borehole tensor strainmeters, such as RZB strainmeter [5], YRY strainmeter [10], and GTSM (Gladwin Tensor Strainmeter) strainmeter [11,12], have been developed and installed in Plate Boundary Observatory (PBO) [13,14,15,16,17] and the China Borehole Strainmeter Network [18,19]. Inner-diameter changes of the stainless steel instrument casing are measured by investigate the theoretical frequency response and the corresponding bandwidth of borehole tensor horizontal extensometers (gauges), after the borehole tensor strainmeter is installed at a certain depth of strainmeters [27]. The model of the incident elastic P/S waves scattering by a two-ring borehole is and the measured instrumental strain wave, and the corresponding bandwidth of borehole tensor introduced to investigate the theoretical frequency response between the referenced strain wave and strainmeters for measuring strain waves quantitatively. The influence of the mechanical parameters of the measured instrumental strain wave, and the corresponding bandwidth of borehole tensor the expansive grout the frequency response and bandwidth of borehole strainmeters for the strainmeters foron measuring strain waves quantitatively. Of the expansive grout on the frequency response and bandwidth of borehole tensor strainmeters for the gauge combinations are discussed in detail
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