Continuous Monitoring of Soil-Gas Pressure Fluctuations in Active Seismogenic and Volcanic Environments: Design and Validation of a Novel Experimental Apparatus

Anomalous gaseous emissions from tectonically active fault zones during pre-seismic, co-seismic, and post-seismic phases have been extensively documented in the literature and quantitatively characterized through in situ terrestrial measurements and remote sensing methodologies. The prevailing paradigm posits that seismotectonic activity induces the mobilization of soil gases through multifaceted geomechanical, geophysical, and hydrogeological processes. In volcanic environments, magmatic volatiles undergo exsolution during ascent as a consequence of progressive decompression and are subsequently discharged through hydrothermal systems and structurally-controlled conduit networks. Despite significant advances in understanding these phenomena, critical knowledge gaps persist regarding the high-resolution temporal characterization of subsurface gas transport dynamics. This investigation addresses these limitations through the following research objectives:

(i) Development of a novel, cost-effective instrumentation system for quantifying pressure fluctuations in subsurface gas transport. The apparatus was designed based on theoretical frameworks governing spherical gas flux propagation within the pedosphere, enabling continuous high-resolution measurements at 0.2-second temporal intervals (5 Hz sampling frequency).

(ii) Validation experiments under controlled laboratory conditions and field deployments to assess instrumental performance. The system demonstrated exceptional sensitivity to pressure variations (on the order of pascals) and micro-cyclical fluctuations. Analysis of the datasets indicates that this instrumentation substantially enhances the spatiotemporal characterization of degassing dynamics in seismogenic and volcanic regimes, as well as associated geophysical and atmospheric processes.

(iii) Investigation and mathematical modeling of physical and geophysical mechanisms governing subsurface gas transport. This approach facilitated the delineation of boundary conditions and parameterization schemes that accurately represent the natural system.

Preliminary results yielded the following findings:

• Exceptional sensitivity in detecting subsurface gaseous pressure fluctuations, with temporal resolution superior to conventional monitoring systems.
• Operational efficacy in low-permeability conditions.
• Discriminatory capability for resolving pressure oscillation cycles across multiple temporal scales, ranging from sub-second to diurnal periodicities.
• Corroboration that high-frequency temporal sampling is essential for detecting transient degassing processes and discriminating endogenous geophysical signals from exogenous atmospheric phenomena.

The results demonstrate promises for advancing continuous monitoring in seismically and volcanically active regions. This instrumentation has potential applications in geophysical fluid dynamics, particularly for characterizing natural degassing phenomena and their coupling with seismotectonic and volcanic processes. Comprehensive interpretation requires integration of pressure measurements with complementary geochemical, seismological, geodetic, and meteorological datasets to elucidate mechanisms governing subsurface degassing and their utility as precursory indicators. The high-frequency sampling enables resolution of micro-cyclical events and transient pressure anomalies undetectable through conventional monitoring, thereby establishing new avenues for investigating coupled Earth system processes.