Inflation or deflation? New results for Mayon Volcano applying elastic‐gravitational modeling

Abstract

Abstract. Volcanic activity produces deformation and gravity changes that many times can be used as precursors of future eruptions. Applying geodetic techniques to monitoring activity involves interpretation using deformation models. Usually, the observed changes of the deformation and gravity fields are interpreted seperately, not in a joint inversion. It can be difficult, if not impossible, to interpret the data coherently or correctly in terms of the characteristics of the intrusion or the deflation derived from the gravity changes with purely elastic models, as in the case of Mayon Volcano, Phillipines. We show that elastic-gravitational models can be used to interpret these cases simultaneously leading to a result that is more plausible on the basis of the available information. Thus, we may need to change the philosophy normally used to interpret geodetic observations. Interpretation as proposed in this work can significantly improve the possibility of predicting future eruptions.

Interpretation of 1992–1994 Gravity Changes around Mayon Volcano, Philippines, Using Point Sources

“…The different accuracies of the three components of the source result from the relative geometrical configuration of the observation points and the source. If we consider the estimated errors for location, these results are rather similar to those obtained by FERNA´NDEZ et al (2001). TIAMPO et al (2004a,b) andTIEDE et al (2005) developed a different kind of sensitivity analysis for the source fit based on the simulated effects of changes in the source parameters.…”

“…This model is based on a redistribution of the mass via the migration of magma down the vent system and can explain about 50% of the magnitude and distribution of the observed gravity changes. FERNA´NDEZ et al (2001) and TIAMPO et al (2004a) used a genetic algorithm for an inversion based on an Vol. 164, 2007 Interpretation of Gravity Changes around Mayon elastic-gravitational model, which introduces a long-wavelength effect and can combine the gravity and deformation fields.…”

“…It is perhaps too small, shallow and displaced from the summit. FERNA´NDEZ et al (2001) and TIAMPO et al (2004b) suggested a similar source (0.47 MU with a depth of 1.95 km below the base of the volcano). By trying a two-source model, we observe that now a nearly centered main positive source is inferred and a secondary unclear deep source is introduced, which explains the existence of a discontinuity pattern in the gravity variations, nearly coincident with the San Vicente-Linao Fault.…”

4D volcano gravimetry

“…The source parameters ͑size, position, amount and density of the redistributed mass, etc.͒ are then retrieved by fitting observed and calculated data through an appropriate inversion scheme. Many studies have proved that this approach can supply unique insights into the processes that lead to unrest ͑e.g., Battaglia et al, 2003b;Berrino, 1994;Bonafede and Mazzanti, 1998;Branca et al, 2003;Charco et al, 2007c;Currenti et al, 2007;Eggers, 1987;Fernández et al, 2001b;Furuya et al, 2003b;Gottsmann et al, 2005;Jachens and Roberts, 1985;Jousset and Okada, 1999;Okubo et al, 1991;and Rymer, 1994͒. Major shortcomings of this approach are that the wrong model might be used to fit the observed data because different elastic models can produce similar effects, and that the simplifications ͑e.g., the assumption that the crust is a homogenous, isotropic, elastic medium͒ that make analytical models tractable can yield misleading volcanological interpretations.…”

“…͑see, e.g., Rundle, 1980Rundle, , 1982Fernández and Rundle, 1994;Fernández et al, 2001aFernández et al, , 2001bFernández et al, 2006͒ represents the emplacement of magma at some depth. The mass and its interaction with the surrounding medium can vary the pattern of gravity change and produce measurable gravity anomalies.…”