Built into everything they do is a number called the b value\u2014a measure of how large the number of little quakes is relative to the number of large ones. When magma intrudes by pushing up, it breaks up the rock surrounding it, and small tremors are created in sets. These small quakes increase the b value. When stress is building and pressure accumulates, the small quakes occur less frequently and larger ones dominate, decreasing the b value.<\/p>\n
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Crater at the top of Mount Etna. (CREDIT: Shutterstock)<\/p>\n
\u201cThose movements in the b value describe the manner that stress in the volcano varies,\u201d explained Firetto Carlino. \u201cSince increasing magma that rises alters that stress, tracking the b value can assist in revealing multiple stages of magma transport from deep to surface.\u201d<\/p>\n
Two Decades of Data Beneath the Surface<\/p>\n
To map out these shifts, the researchers divided the crust beneath Etna into slices\u2014less than 3 kilometers thick to more than 17 kilometers beneath the surface\u2014and identified 11 primary volumes in which earthquake energy was accumulated. By comparing the patterns of quakes<\/a> to ground deformation picked up by GPS stations on the slopes of Etna, they found one area that stood out: an area 3 to 7 kilometers deep on the volcano\u2019s east flank.<\/p>\n This middle-crustal level, labeled \u201cV6\u201d in the study, displayed a direct correspondence between inflation of the volcano\u2019s surface and seismic strain. That is to say, whenever the volcano inflated, which meant magma was ascending, tiny earthquakes skyrocketed within that very same depth zone.<\/p>\n This connection suggests that the 3\u20137 km level is a critical staging zone, where magma piles up and pressures build before continuing to the surface. Higher levels have small earthquakes ride shotgun with dike intrusion and near-surface fracturing when eruptions occur. Below, deeper areas seem to feed magma up but are less immediately connected with surface deformation.<\/p>\n Mt. Etna seismicity and b values from 2005 to 2024. (CREDIT: Science Advances)<\/p>\n Mapping Magma\u2019s Journey<\/p>\n Mount Etna\u2019s crust is similarly thick, about 30 kilometers (19 miles) deep, and cut by a complex strike-slip fault where the African and European tectonic plates meet. Magma starts at a deep reservoir about 11 kilometers below sea level, rises to intermediate storage systems from 3 to 7 kilometers deep, then feeds shallow chambers close to the summit.<\/p>\n The INGV team concludes that the b value is a surprisingly good indication of where and how magma moves along this route. Areas with hot fluids and fractures have high b values, meaning many small earthquakes. Areas with high stress and fewer fractures have lower values, meaning fewer but larger earthquakes<\/a>.<\/p>\n By following what this ratio does over time, scientists can essentially plot magma\u2019s ascension in real-time. A surge in small quakes at a certain depth can be an indicator of magma forcing its way up, and a sudden drop can be a sign of pressure building for a larger event.<\/p>\n A New Type of Early Warning<\/p>\n This process worked especially well when the group used it on the recent history of Etna. Before the volcano\u2019s eruption in June 2025, which sent a 6.5-kilometer (4-mile) ash plume into the atmosphere, early warning signs manifested in the b value months before any gas emission or surface deformation.<\/p>\n Time series of the b value from January 2016 to the end of 2024, calculated for the (A) deep [time series \u2013 deep (TS-D)], (B) intermediate [time series \u2013 intermediate (TS-I)], and (C) shallow [time series \u2013 shallow (TS-S)] seismogenic volumes of interest in Etna\u2019s plumbing system. (CREDIT: Science Advances)<\/p>\n That timing may be critical for future monitoring. \u201cOur findings indicate that b value monitoring may have predicted volcanic crises,\u201d the authors stated. Being able to pick up on such signals beforehand may provide local officials with additional time to alert citizens and organize evacuations.<\/p>\n Because there are so many quakes that can be detected annually by Etna, it\u2019s an ideal testing ground. But the method can also be applied to other active volcanoes\u2014anywhere there is a good seismic network<\/a> and well-mapped crustal structure.<\/p>\n Challenges Beneath the Data<\/p>\n However, scientists say that there is no single volcano that is identical to another. Precise attention and good data are required in the interpretation of changes in b values. Several factors, ranging from local tectonic stress to landslides and fault displacement, impact earthquake statistics.<\/p>\n To make this tool effective globally, scientists need dense arrays of seismometers, accurate location of quakes, and constant monitoring of other indications of volcanic activity<\/a> like gas emission and heat movement. Even supposing those are available, it remains a human challenge as much as a scientific one to translate all that information into clear, actionable warnings for the public.<\/p>\n Conceptual model of Etna\u2019s plumbing system, showing the main structural features of the region and magma storages. (CREDIT: Science Advances)<\/p>\n Practical Implications of the Research<\/p>\n This study gives volcanologists a more precise tool to read magma\u2019s behavior and make better eruption forecasts. Being able to track the b value allows researchers to identify where the magma is accumulating and if it will keep rising. That can improve safety for populations near active volcanoes\u2014not just in Sicily but everywhere.<\/p>\n On the ground, raising b values could be a sign of active but secure magma flow<\/a>, while reducing values could signal experts to an unstable pressure buildup. With surface deformation information added, the technique could issue warnings sooner than current systems that track gas and surface-visible activity alone.<\/p>\n For people living on Etna\u2019s slopes\u2014and for the millions across the world who have volcanoes looming over them\u2014this research holds the promise to tame eruptions of nature.<\/p>\n Research findings are available online in the journal Science Advances<\/a>.<\/p>\n Related Stories<\/p>\n![\"Mt.](\"https:\/\/www.europesays.com\/ie\/wp-content\/uploads\/2025\/10\/5d992d83ade3aa191918e3d7551c23eb.jpeg\"\/)
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