In-situ density and litho-constrained modeling of gravity data in the Los Humeros geothermal field, Mexico

To support improved exploration of geothermal reservoirs, this study evaluates the effectiveness of various density parameterization strategies for constraining gravity modeling and inversion in the complex volcanic setting of the Los Humeros Geothermal Field (LHGF), Mexico. Forward modeling results show a relatively poor fit between observed and computed gravity data across all tested scenarios, with only limited improvement from optimized initial densities. Incorporating compaction effects and saturated porosity densities significantly reduced the misfit during inversion.Detailed misfit evaluation reveals that our initial density values consistently underestimated optimal densities by 60–100 kg/m³. The misfit did not vary with depth, ruling out systematic compaction underestimation, and the low salinity of reservoir fluids (≤ 4 g/L) indicates that salinity effects are negligible. A multi-modal density approach did not improve the fit and introduced skewness, likely due to volumetric estimates of lithologies based on limited available data for the individual units.Inversion tests with varying probabilities of density and geometry changes revealed that for the LHGF a 70:30 ratio produced the most optimal model, confirming the overall consistency of the initial 3-D geological model with observed gravity data. Smaller density variations in pre-caldera units suggest greater homogeneity, while fault zones likely contribute to localized heterogeneity in the underlying units. Our results do not distinguish between the conventional and superheated sectors of the LHGF, highlighting that gravity anomalies in this volcanic system primarily reflect the geological structure rather than thermal or fluid characteristics.Finally, our methodology provides a practical framework for quantifying uncertainty of 3-D geological models.