Frequency‐Dependent Seismic Velocity Variations Reveal Layered Aquifer Behavior Under Groundwater Fluctuations

Abstract Frequency‐dependent seismic velocity variations (dv/v) provide depth‐resolved constraints on aquifer behavior under groundwater fluctuations. We analyze 17 years of dv/v time series from ambient noise interferometry in the Chiang Mai Basin, Thailand, and observe contrasting dv/v behavior below and above 1 Hz. By integrating GPS, meteorological, and GWL data with poroelastic stress modeling, we disentangle the contemporaneous effects of pore saturation, pore pressure change, and mass loading. Our results show that the pore saturation and pore pressure change jointly influence shallow aquifer layers, while mass loading governs deeper responses. This depth‐dependent interplay highlights the importance of effective stress modeling in interpreting dv/v patterns and the potential of passive seismic techniques to monitor layered hydromechanical processes in aquifer systems.