Strategies in the processing and analysis of continuous gravity record in active volcanic areas: the case of Mt. Vesuvius

J Hinderer J Hinderer,U Riccardi U Riccardi,G Berrino G Berrino,G Corrado G Corrado

doi:10.4401/ag-3039

Abstract

This research is intended to describe new strategies in the processing and analysis of continuous gravity records collected in active volcanic areas and to assess how permanent gravity stations can improve the geophysical monitoring of a volcano. The experience of 15 years in continuous gravity monitoring on Mt. Vesuvius is discussed. Several geodynamic phenomena can produce temporal gravity changes. An eruption, for instance, is associated with the ascent of magma producing changes in the density distribution at depth, and leading to ground deformation and gravity changes The amplitude of such gravity variations is often quite small, in the order of 10-102 nms-2, so their detection requires high quality data and a rigorous procedure to isolate from the records those weak gravity signals coming from different sources. Ideally we need gravity signals free of all effects which are not of volcanic origin. Therefore solid Earth tide, ocean and atmospheric loading, instrumental drift or any kind of disturbances other than due to the volcano dynamics have to be removed. The state of the art on the modelling of the solid Earth tide is reviewed. The atmospheric dynamics is one of the main sources precluding the detection of small gravity signals. The most advanced methods to reduce the atmospheric effects on gravity are presented. As the variations of the calibration factors can prevent the repeatability of high-precision measurements, new approaches to model the instrumental response of mechanical gravimeters are proposed too. Moreover, a strategy for an accurate modelling of the instrumental drift and to distinguish it from longterm gravity changes is suggested.

Highlights

A wide set of dynamic phenomena can produce temporal gravity changes, with a spec-U
The goal of this paper is to describe new strategies in the processing and analyses of continuous gravity record collected in active volcanic areas
The above described results show how the continuous gravity record on active volcanoes could be a useful investigative tool to detect volcanic inputs, but much care must be taken to remove from the recorded signals the effects due to the instrumental response and non-volcanic sources

Summary

Introduction

A wide set of dynamic phenomena (i.e. geodynamics, seismicity, volcanic activity) can produce temporal gravity changes, with a spec-. Instrumental sensitivity can change, not always linearly, as a consequence of mechanical perturbations and the noise level at the gravity station. As changes in instrumental sensitivity can prevent the repeatability of measurements and affect the phase and amplitude of the recorded gravity signals, the accurate calibration of gravimeters plays a key role in high precision gravity measurements (Riccardi et al, 2002). More detailed discussion concerning the instrumental sensitivity changes on the occasion of large earthquakes is given in Riccardi et al (2002) and Berrino and Riccardi (2004) They suggest a mechanical perturbation of the sensor, due to some dominant frequencies of the noise at the station on the occasion of large earthquakes. These instrumental disturbances due to large earthquakes can last several weeks

Ocean loading and atmospheric reduction

Atmospheric reduction by means of a barometric array

Findings

Conclusions