Characteristics of hydroseismograms in Jingle well, China
Abstract Hydroseismograms reflect the oscillations of well water levels caused by seismic waves. In this study, the relationships between the hydroseismogram oscillation amplitude and three factors (seismic magnitude, epicentral distance, and focal depth) in Jingle well, China were analyzed. The results revealed that hydroseismogram amplitude increases exponentially with seismic magnitude as H mag = 7.848 × 10 - 8 × e 2.1690 × m + 0.047 ( m > M w 5.8 ) ( m – seismic magnitude), decreases exponentially with epicentral distance as H dis = - 2.1108 × 10 - 5 × e 2.3864 × γ + 0.011 ( γ – epicentral distance), and decreases exponentially with focal depth as H dep = - 1.6438 × 10 - 3 × e 0.0254 × d - 0.203 (d is focal depth). However, these relationships become uncertain when the epicentral distance exceeds 4000 km and are not applicable to nuclear explosions. Based upon the single well–aquifer model constructed for Jingle well, the amplification ( μ ) of the water level oscillation by ground vibrations μ = A b A a = R 2 - r 2 r 2 depends on the frequency of the water-level oscillations. For relatively high-frequency oscillations (caused by earthquakes with relatively small epicentral distances), the amplification will be small, while for low-frequency oscillations (caused by earthquakes with relatively large epicentral distances), the amplification will be large. Using the S-transform, the dominant hydroseismogram period increases with the epicentral distance as τ = 0.5826 × γ + 12.51 , which means that the amplification ( μ ) increases with the epicentral distance. Of course, the amplitude of ground oscillations will be greatly attenuated with increasing epicentral distance. Due to the anisotropy of the earth and seismic wave superposition, the relationships between the hydroseismogram amplitude and the seismic magnitude, epicentral distance, and focal depth become blurred or even uncertain with increasing epicentral distance and focal depth, leading to poor goodness-of-fit between the dominant hydroseismogram period and epicentral distance. The quantitative relationships between the hydroseismogram amplitude and the seismic magnitude, epicentral distance, and focal depth, which determine the ratio between the amplitudes of water-level oscillations and ground vibrations and the relationship between groundwater oscillations and seismic wave transmission, are proposed for the first time in the present work. These results will improve understanding of hydrogeological conditions and could also be important in identifying reliable earthquake precursors.