Electrokinetic Contributions to Self‐Potential Signals From Magmatic Stressing

Abstract

Volcanic unrest is often accompanied by anomalous geophysical and geochemical signals that are generally attributed to processes within the subvolcanic plumbing system (Salvage et al., 2017). Precise eruption forecasting remains a key issue in volcanology and depends on the correlation of volcanic precursors to subsurface causative mechanisms (Magee et al., 2018; Sparks, 2003). A major challenge in volcano monitoring is to establish whether a period of volcanic unrest will culminate in an eruption or wane without eruptive activity (Gottsmann et al., 2017; Phillipson et al., 2013; Sparks et al., 2012). Volcano deformation is a prevalent observable during volcanic unrest (Sparks et al., 2012) caused by pressure changes in the magma reservoir (Lisowski, 2006). Geodetic modeling exploits observed surface displacement to constrain source properties (e.g., pressure changes) and mechanisms driving unrest periods (e.g.,

Multiphysics Modeling of Volcanic Unrest at Mt. Ruapehu (New Zealand)

“…However, it has been shown that a two-way coupling approach is more applicable for temporally protracted perturbations (Neuzil, 2003;Rutqvist et al, 2002), where subsurface strain affects hydraulic rock properties (e.g., κ, ϕ) which in turn govern the flow behaviour and in turn stresses and strains. Similar to studies by e.g., Hutnak et al (2009); Cur- Neither of our simulations account for the temperature dependence of parameters such as permeability (Ikard & Revil, 2014), fluid properties (Arens et al, 2020) or elastic parameters (Head et al, 2021), all of which have an effect on geophysical anomalies modelled in our study; a dedicated analysis is required to assess this influence. Although we neglect thermoelectric processes caused by strong thermal gradients (Corwin & Hoover, 1979;Fitterman & Corwin, 1982) in the HTU simulations, we find that for a maximum temperature change of 0.18 • C (unrest III) at the plateau, the thermoelectric potential (TEP) is ± 0.3 mV and 0.1 mV using a thermoelectric coupling coefficient of ± 1.5 mV/ • C and ± 0.5 mV/ • C (Revil & Mahardika, 2013;Ikard & Revil, 2014), respectively.…”

“…Neither of our simulations account for the temperature dependence of parameters such as permeability (Ikard & Revil, 2014), fluid properties (Arens et al., 2020) or elastic parameters (Head et al., 2021), all of which have an effect on geophysical anomalies modeled in our study; a dedicated analysis is required to assess this influence. Although we neglect thermoelectric processes caused by strong thermal gradients (Corwin & Hoover, 1979; Fitterman & Corwin, 1982) in the HTU simulations, we find that for a maximum temperature change of 0.18°C (unrest III) at the plateau, the thermoelectric potential (TEP) is ±0.3 and 0.1 mV using a thermoelectric coupling coefficient of ±1.5 mV/°C and ±0.5 mV/°C (Ikard & Revil, 2014; Revil & Mahardika, 2013), respectively.…”

“…We solve poroelastic responses and strain-induced self-potential anomalies in the sub-domains (HTS, TZ, edifice) above 1.5 km a.m.s.l. using the approaches proposed in (Strehlow et al, 2015;Arens et al, 2020). The initial pore pressure distributions for straininduced fluid flow at t = 0 is taken from the background HTU simulation (see section 3.3.2).…”

“…Inherent model limitations for MU simulations have been described in detail in Arens et al (2020). Our HTU simulations do not account for super-critical conditions, although there is evidence for pressures and temperatures in hydrothermal systems at active volcanoes exceeding the critical point of water (Reinsch et al, 2017).…”

“…Hybrid unrest is caused by the modulation of subsurface stresses and strains from magma rejuvenation by poroelastic responses in volcano-hydrological reservoirs (e.g., aquifers, hydrothermal systems; Strehlow et al (2015); Newhall et al (2001); Shibata and Akita (2001); Strehlow et al (2020)). Furthermore, strain-induced fluid flow caused by poroelastic responses to magmatic stressing or ascending hydrothermal fluids generate selfpotential (SP) anomalies (Arens et al, 2020;Corwin & Hoover, 1979;Zlotnicki & Nishida, 2003;Revil, Naudet, et al, 2003).…”