New Results at Mayon, Philippines, from a Joint Inversion of Gravity and Deformation Measurements

Abstract

In this paper, we detail the combination of the genetic algorithm (GA) inversion technique with the elastic-gravitational model originally developed by Rundle and subsequently refined by Ferna´ndez and others. A sensitivity analysis is performed for the joint inversion of deformation and gravity to each of the model parameters, illustrating the importance of proper identification of both the strengths and limitations of any source model inversion, and this technique in particular. There is a practical comparison of the theoretical results with the inversion of geodetic data observed at the Mayon volcano in the Philippines, where there are gravity changes without significant deformation, after the 1993 eruption.

On the interpretation of vertical gravity gradients produced by magmatic intrusions

“…Taking into account the results by Rundle (1982), Fernández and Rundle (1994a,b), Fernández et al (1997Fernández et al ( , 2001a and Tiampo et al (2004), it is clear that using two sources of loading, a point mass and a pressurized cavity, we are able to calculate theoretically a number of different gradient cases. One example of the problems that arise in the interpretation of direct gravity and deformation measurements is that the total uplift or subsidence at a selected radius r can be zero without the surface gravity change being zero, and vice versa.…”

“…While many number of inversion techniques are available for this purpose, the non-linear GA methodology proved to be an efficient and effective solution. A detailed description of the GA methodology can be found in Tiampo et al (2000Tiampo et al ( , 2004.…”

“…The results by Rundle (1982), Fernández et al (1997Fernández et al ( , 2001a and Tiampo et al (2004) suggest that using the elastic-gravitational deformation model with two sources of loading, a point mass and a pressurized cavity, we can explain many different gradients, e.g., cases where uplift (or subduction) at a selected horizontal distance from the intrusion at surface can be zero or almost zero without the total surface gravity vanishing.…”

“…Rundle (1980Rundle ( , 1982 presented an elastic-gravitational model that considers a stratified half-space of homogeneous layers and takes into account the interaction between the mass of the intrusion, the gravity field and the effect caused by the change of pressure in the magmatic system. Fernández and Rundle (1994a,b), Fernández et al (1997Fernández et al ( , 2001a and Tiampo et al (2004) show that the gravitational coupling effects can be fundamental for adjusting and properly explaining the gravity changes measured in active zones. Vertical displacements and gravity changes produced by pressure increases and the mass of the intrusion have different signs (Rundle, 1982).…”