# Multidisciplinary Study of Mud Emissions Following the 2016 Norcia Earthquake
## 1 Introduction
Above, we have outlined that earthquakes may cause gas bubbles' growth or nucleation, which may encourage the rising of mudflow from deep. The gases detected venting from mud volcanoes are composed predominantly of methane, although some mud volcanoes emit carbon dioxide or nitrogen-enriched gases. Some gases contain dry biogenic methane, others heavier, thermogenic methane (the biochemical gases occur both under surface conditions and at depths up to 1200-2000 m). Usually, the roots of mud volcanoes lay below these depths, and it can be expected that these gases or organic matter will be reworked thermogenically, producing the so-called \"thermogenic\" gas. The gases of thermogenic origin contain methane accompanied by small amounts of methane homologs and oil leakage. The gases come mainly from source rocks and muddy sediments (clays, shales, mudstones, siltstones, and marls), but shallower layers through which the mud breccia passes may also contribute to the gas. Organic matter makes up a substantial part of freshly deposited mud. Post-depositional transformation leads to active biogenic and thermogenic gas generation, \"which is an important added factor which tends to accentuate, or even create, their overpressured, under-compacted state, both by building up additional internal pressure and also by impeding fluid expulsion because of the development of a second phase in the pore fluid\" [31]. The high pore fluid pressure is a characteristic feature of all mud volcano areas [31; 32] and may be more than twice the hydrostatic pressure and may even be greater than the weight of the overburden. Therefore, mud volcanoes may be strictly connected to earthquake and fault activity [33]. Indeed, the location and activity of mud volcanoes are sometimes used as indicators of the presence of active fault systems [34]. Earthquakes can influence the rise of mudflow and therefore the eruptions of mud volcanoes by increasing fluid pressure, causing the growth or nucleation of gas bubbles or developing a hydraulic connection between the source or loss of strength, usually located at \(\sim\)1-3 km depth ([35] and references therein), but greater depths are possible [33], and at the surface [35]. In addition, a close correlation exists between the magnitude of an earthquake and the distance at which a mud volcano eruption can occur ([35] and references therein). However, in the experimental studies of [PERSON] et al. [35], in which submitted mud suspensions were subjected to cyclic shear under seismic frequencies and amplitudes, the loss of strength occurred at strain amplitudes greater than \(10^{-3}\), a value much larger than the peak dynamic strain associated with earthquakes that may have triggered mud eruptions. [PERSON] et al. [36] show that applying any finite amplitude vibration suppresses the yield stress of gravitational suspensions that, under vibration, behave as viscous fluids. Their viscosity varies with particle size, suspending fluid viscosity, and vibration amplitude and frequency. However, the real cause/trigger of mud emissions is not well understood. Here, we focus on the case studies of Santa Vittoria in Matenano and Monteleone di Fermo (central