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The debate about the conceptual model of mud volcanoes functioning is still alive in the literature. A large part of the literature focuses on the characterization of the deep reservoir where expelled fluids are expected to originate. Another part of literature is focused on the study of the shallow system of mud volcanoes, which could influence the short‐term variations in mud volcanoes activity. We present and analyze a new data set of micro‐gravimetric data to study the area of the Nirano Salse, Italy. Unlike what is commonly assumed for the study area, our results suggest that the geomorphology of the Nirano Salse is not related to a caldera collapse above a shallow mud chamber, but to the surface expression of slip distribution of a fault termination along which the fluids ascended to the surface. We believe that gravimetric data can significantly improve the study of hydrocarbon seeps and mud volcanism. Plain Language Summary: Mud volcanoes are broadly distributed throughout the globe, both on‐and off‐shore. They are formed by the episodic eruption of mud and rock fragments. The eruptions are mainly driven by of gravitative instability, due to the overall low density of clay on surrounding soil types and fluid overpressures. To date, a physical conceptual model of the area of Nirano Salse (Northern Italy), ascribes the mud eruptions to the presence of over‐pressurized fluids that are expelled from a main deep reservoir. The latter is put into communication with the surface due to the episodical reactivation of pre‐existing faults or pipes. The debate about this conceptual model is still open. To improve it, a new data set of gravimetric data was acquired during 2022. Our results suggest that the morphology of the study area is due to the presence of an almost vertical fault, which acts as a preferential route for the ascent of deep fluids. Key Points: A microgravimetric survey coupled with laboratory density measurements allows to image the shallow to medium subsurface below mud volcanoesGravimetric data allow to distinguish between morphologies due to caldera collapse and the surface expression of slip along a faultFor the first time the attenuation volume caused by mud intrusion is imaged by gravimetry along a fault [ABSTRACT FROM AUTHOR]

The Nirano Salse, known since the Roman Times, are one of the most beautiful and scenic mud volcanoes areas of Italy with thousands of visitors every year. In this work, we apply novel (for the context) hydrogeological techniques to characterize mud levels in the Salse by means of GPS-RTK positioning and continuous level logging within mud conduits. This is important to quantify the gas–liquid ratio in the conduits and evaluate the potential for dangerous abrupt mud eruptions. The results presented suggest that different mud levels in mud volcanoes clusters are due to the different gas–liquid ratio in the conduits and not necessarily exclude interconnection at depth, a hypothesis, on the other hand, that seems strengthened by mud level time series correlations. The presence of shallow aquifers at a depth of 5 to 30 m is also supported by our field data and allows us to delineate the boundaries of the shallow mud reservoir—pipes system and its overall shape. The shallow aquifers may provide a temporary storage for the ascending gas and when fluid pressure in these aquifers exceeds the tensional strength of the sedimentary rock, leakage of fluids to the surface would occur. In this case, if the gas–liquid ratio is high, mud volcanoes develop into tall gryphons and tend to have a discontinuous activity with sudden eruptions of mud after long periods of quiescence. This, together with the knowledge of shallow conduits localization has an important implication for site safety in proximity to the mud volcanoes. Our inferences based on mud level relationships to mud extrusion dynamics can be applied to lower risk in other mud volcanoes areas of the world with high geo-tourist visits, such as those of Trinidad, Azerbaijan, and Colombia. [ABSTRACT FROM AUTHOR]