4D volcano gravimetry

Abstract

Time-dependent gravimetric measurements can detect subsurface processes long before magma flow leads to earthquakes or other eruption precursors. The ability of gravity measurements to detect subsurface mass flow is greatly enhanced if gravity measurements are analyzed and modeled with ground-deformation data. Obtaining the maximum information from microgravity studies requires careful evaluation of the layout of network benchmarks, the gravity environmental signal, and the coupling between gravity changes and crustal deformation. When changes in the system under study are fast ͑hours to weeks͒, as in hydrothermal systems and restless volcanoes, continuous gravity observations at selected sites can help to capture many details of the dynamics of the intrusive sources. Despite the instrumental effects, mainly caused by atmospheric temperature, results from monitoring at Mt. Etna volcano show that continuous measurements are a powerful tool for monitoring and studying volcanoes.Several analytical and numerical mathematical models can beused to fit gravity and deformation data. Analytical models offer a closed-form description of the volcanic source. In principle, this allows one to readily infer the relative importance of the source parameters. In active volcanic sites such as Long Valley caldera ͑California, U.S.A.͒ and Campi Flegrei ͑Italy͒, careful use of analytical models and high-quality data sets has produced good results. However, the simplifications that make analytical models tractable might result in misleading volcanological interpretations, particularly when the real crust surrounding the source is far from the homogeneous/isotropic assumption. Using numerical models allows consideration of more realistic descriptions of the sources and of the crust where they are located ͑e.g., vertical and lateral mechanical discontinuities, complex source geometries, and topography͒. Applications at Teide volcano ͑Tenerife͒ and Campi Flegrei demonstrate the importance of this more realistic description in gravity calculations.

Thermomechanical modeling of the Altiplano-Puna deformation anomaly: Multiparameter insights into magma mush reorganization

“…Standard surveying techniques (see Battaglia et al, 2008) were applied, including the establishment of control points as part of individual survey loops to better correct for instrument drift and possible tares.…”

Asymptotic expansion for harmonic functions in the half‐space with a pressurized cavity

“…The simplest approximate solution obtained by asymptotic expansions is due to McTigue when the cavity is a sphere, see [15]. The other few solutions available concern ellipsoidal shapes, dike and faults, see [6,17].…”

“…Additionally, from a geological point of view, sometimes it is reasonable to consider the magma chamber small compared to the distance from the boundary of the half-space, see [6,15,17]; by adding these hypotheses and fixing the geometry of the cavity, some efforts have been done during the last decades to find some explicit or approximate solutions to the mathematical model. The simplest approximate solution obtained by asymptotic expansions is due to McTigue when the cavity is a sphere, see [15].…”

“…The starting evidence is that the magma exerts a force aside the surrounding crust when migrates toward the earth's surface, producing appreciable horizontal and vertical ground displacements, which can be detected by a variety of modern techniques (see the detailed description provided in [17]). As stated in [6], the main questions that emerge when monitoring volcanoes are how to constrain the source of unrest, that is to estimate the parameters related to its depth, dimension, volume and pressure, and how to better asses hazards associated with the unrest. For this purpose, the measurements of crust deformations are a useful tool to study magmatic processes since they are sensitive to changes in the source pressure and volume.…”

Long-term time-lapse microgravity and geotechnical monitoring of relict salt mines, Marston, Cheshire, U. K.

“…Researchers have used time-lapse microgravity surveys to observe temporal site changes in other applications of aquifer storage and recovery (Davis et al, 2008), geothermal reservoirs (Sugihara and Ishido, 2008), volcano eruptions (Battaglia et al, 2008), and CO 2 injection studies (Alnes et al, 2008). Time-lapse microgravity surveys have been undertaken to monitor ground subsidence in which careful data collection and processing were required, but these have been few to-date (see Debeglia and Dupont, 2002;Branston and Styles, 2003).…”