Disaster mitigation

[DM-09] Time-lapse monitoring of the variations of ground conditions caused by rain based on the peak frequency of H/V spectra of microtremors

*Masayuki Kuriyama¹, Hiroaki Sato¹ (1. Central Research Institute of Electric Power Industry (Japan))

Investigation of changes of ground conditions that causes slope failures is critical for disaster prevention of facilities. Strain measurement is one of the general methods to detect the changes of ground conditions and new various measurements, such as laser scanning, have been proposed. Recently, areas at high risk of landslides have been also identified by using high-resolution satellite images.
In a monitoring of changes of ground physical properties, detection of variations of ground conditions associated with the occurrence of earthquakes has been actively conducted using the autocorrelation function (ACF) of both earthquake records and microtremor records. These techniques can also be applied to mitigate slope disasters. Therefore, evaluation of an applicability for other external events, such as heavy rain, is important.
In this study, we propose a method to monitor time-lapse variations of ground conditions based on the peak frequency of the horizontal-to-vertical spectral ratios (H/V spectra) of microtremors, which have high sensitivity to changes in subsurface velocity structure. In the monitoring by using the H/V spectra, identification of the target peak frequency to be monitored is an issue when several peak frequencies are seen in the spectrum. Therefore, in order to clarify the relationship between the depth range of target strata and the peak frequency, we conducted microtremor array exploration and found the target peak frequency which correspond to the subsurface structure shallower than engineering bed rock. In addition, we show an effectiveness of the proposed method by demonstrating the good correlation between the variations of the target peak frequency and precipitation.