Volcanic signatures in time gravity variations during the volcanic unrest on El Hierro (Canary Islands)

Abstract

Gravity changes occurring during the initial stage of the 2011-2012 El Hierro submarine eruption are interpreted in terms of the preeruptive signatures during the episode of unrest. Continuous gravity measurements were made at two sites on the island using the relative spring gravimeter LaCoste and Romberg gPhone-054. On 15 September 2011, an observed gravity decrease of 45 μGal, associated with the southward migration of seismic epicenters, is consistent with a lateral magma migration that occurred beneath the volcanic edifice, an apparently clear precursor of the eruption that took place 25 days later on 10 October 2011. High-frequency gravity signals also appeared on 6-11 October 2011, pointing to an occurring interaction between a magmatic intrusion and the ocean floor. These important gravity changes, with amplitudes varying from 10 to À90 μGal, during the first 3 days following the onset of the eruption are consistent with the northward migration of the eruptive focus along an active eruptive fissure. An apparent correlation of gravity variations with body tide vertical strain was also noted, which could indicate that concurrent tidal triggering occurred during the initial stage of the eruption.

The 8 October 2011 Earthquake at El Hierro (Mw 4.0): Focal Mechanisms of the Mainshock and Its Foreshocks

“…Another interesting feature revealed in our study is that the main earthquake was the largest and latest part of a process that started the day before (7 October 2011, 22:14 UTC). This time coincides to when López et al (2014) reports the beginning of the upward seismic hypocenter migration, the maximum release of seismic energy, and reaching the maximum strain rate of the preeruptive swarm and the first days of the eruption, and with gravity changes reported in Sainz-Maza Aparicio et al (2014). Ibáñez et al (2012) also observed a considerable decrease in b-values in that period compared to the previous weeks of the unrest.…”

The Benefits of Using a Network of Superconducting Gravimeters to Monitor and Study Active Volcanoes

“…Indeed, past studies have shown that the combined effect of instrumental drift and environmental factors (mostly, ambient temperature) may induce strong apparent gravity changes that are difficult to predict since highly nonlinear, instrument‐specific, and frequency‐dependent modeling schemes are required (Andò & Carbone, ). If a suitable setup is adopted for the field stations, these effects become negligible over short intervals, which explains why most past studies at active volcanoes have focused on the analysis of continuous gravity observations over time scales of minutes to a few days (e.g., Branca et al, ; Carbone et al, , , , , ; Carbone & Poland, ; Gottsmann et al, ; Poland & Carbone, , ; Sainz‐Maza Aparicio et al, ).…”

Absolute gravity change associated with magma mass movement in the conduit of Asama Volcano (Central Japan), revealed by physical modeling of hydrological gravity disturbances

“…(17)). An arbitrary constant value was subtracted from the gravity values, so as to conform the maximum of the daily average gravity to 0 Here we discuss several effects of mass distributions associated with volcanism [e.g., Furuya et al, 2003;Del Negro et al, 2013;Aparicio et al, 2014], in order to explain the physical mechanism of the residual gravity observed at Asama Volcano in 2004 ( Figure 9). We also utilize the observed data other than gravity, such as the emission rate of volcanic gas, because each effect of mass distribution cannot be isolated from the observed gravity values (= the integral of all of mass distributions).…”