Spatial and temporal influence of rainfall on crustal pore pressure based on seismic velocity monitoring

Abstract

Crustal pore pressure, which controls the activities of earthquakes and volcanoes, varies in response to rainfall. The status of pore pressure can be inferred from observed changes in seismic velocity. In this study, we investigate the response of crustal pore pressure to rainfall in southwestern Japan based on time series of seismic velocity derived from ambient noise seismic interferometry. To consider the heterogeneity of the area, rainfall and seismic velocity obtained at each location were directly compared. We used a band-pass filter to distinguish the rainfall variability from sea level and atmospheric pressure, and then calculated the cross-correlation between rainfall and variations in S-wave velocity (Vs). A mostly negative correlation between rainfall and Vs changes indicates groundwater recharge by rainfall, which increases pore pressure. The correlations differ between locations, where most of the observation stations with clear negative cross-correlations were located in areas of granite. On the other hand, we could not observe clear correlations in steep mountain areas, possibly because water flows through river without percolation. This finding suggests that geographical features contribute to the imprint of rainfall on deep formation pore pressure. We further modelled pore pressure change due to rainfall based on diffusion mechanism. A strong negative correlation between pore pressure estimated from rainfall and Vs indicates that the Vs variations are triggered by pore pressure diffusion in the deep formation. Our modelling results show a spatial variation of diffusion parameter which controls the pore pressure in deep formation. By linking the variations in seismic velocity and crustal pore pressure spatially, this study shows that seismic monitoring may be useful in evaluating earthquake triggering processes or volcanic activity.

Controls on Seasonal Variations of Crustal Seismic Velocity in Taiwan Using Single‐Station Cross‐Component Analysis of Ambient Noise Interferometry

“…The lack of correlation between the pore pressure changes and dv/v in the deep mountain areas in Andajani et al. (2020) also seems contradictory to our observations, where the good correlations appear mainly at the stations in the foothill and mountain areas. We believe both observations can be explained from fracture development controlled by different lithology and tectonic activity.…”

“…The qualitative match seen between the dv/v and the rainy season suggests a possible influence of rainfall. Rainfall‐induced pore pressure changes rather than rainfall itself have been suggested to cause the seismic velocity variations in many places (Andajani et al., 2020; Donaldson et al., 2019; Liu et al., 2020; Rivet et al., 2015; Wang et al., 2017). Therefore, we use a one‐dimensional fully coupled diffusion equation (Talwani et al., 2007) to compute the pore pressure changes.…”

“…Using a similar approach in the same 0.1–0.9 Hz frequency band, Andajani et al. (2020) estimated diffusion rates ranging from 0.02 to 1.0 m 2 /s for the Chugoku and Shikoku regions in southwestern Japan. They found that the correlations between the pore pressure changes and dv/v differ between locations, with clear correlations observed at the stations in granitic regions but not in the steep mountain areas.…”

Continuous monitoring system for safe managements of CO2 storage and geothermal reservoirs

“…Furthermore, the overburden imposed by precipitation may change the stress state and pore pressure within the deep crust (with low permeability), affecting seismic velocity. Similar temporal velocity variation associated with precipitation can be observed by ambient noise analysis 13 .…”

“…Since production and reduction wells in geothermal fields are also widely distributed in the geothermal field, a monitoring system for the multi geothermal reservoirs is crucial for sustainable geothermal power generation 9 Monitoring, in sum, provides key information for effective and safe reservoir management for CO2 reduction. In addition to the CO2 storage and geothermal power, the earth monitoring over a spatial range from small reservoirs to the crustal domain is a central technology for energy exploration (e.g., petroleum exploration) 10 , environmental projects (e.g., aquifer utilization) 11 , and disaster prevention (e.g., earthquake fault and volcano monitoring) 12, 13 .…”