Vp/Vs VARIATIONS DURING PRE-ERUPTIONS SEISMICSWARMS AS A PRECURSORY SIGNAL FOR VOLCANICERUPTION

Fagradalsfjall is located in the central part of the Reykjanes Peninsula and is part of the volcanicbelt located between the Svartsengi and Krsuvik systems in Iceland. In this paper, we examined the۲۰۲۱ Fagradalsfjall swarm, which began with a ۵.۳ magnitude ML earthquake on ۲۴ February andcontinued for about a month before ending with an eruption on March ۱۹. This swarm was acontinuation of the July ۲۰۱۷ (ML < ۳.۷), December ۲۰۱۹ (ML < ۳.۷) and July ۲۰۲۰ (ML < ۵) in thisregion. We employ the robust double-difference Wadati method to assess the in-situ Vp/Vs ratio,serving as a means to monitor the presssence of magma across various temporal and spatial intervals.Our findings reveal a declining trend in the cumulative Vp/Vs ratio throughout the entire pre-eruptionswarm period. Additionally, the calculated Vp/Vs value for this swarm is lower than that observed inprevious swarms and in the background seismicity. This trend suggests an increasing presence ofoverpressurized gas and water vapor within the medium in this phase

کلیدواژه ها:

Vp/Vs Ratio ، Double-Difference Wadati Method ، Magma ، Fagradalsfjall ، Swarm ، Volcanic Eruption