The Campi Flegrei to the west of Naples rank among the most sensitive volcanic regions in Europe. For years, researchers have been recording increasing seismic activitythere, accompanied by a slow but continuous ground uplift. A recent scientific study by the GFZ Helmholtz Centre for Geosciences now sheds new light on the complex processes beneath the surface.
Notable changes since around 2005
At the heart of the analysis is the relationship between ground uplift and earthquake activity. The researchers conclude that both phenomena are closely interlinked, though this relationship is considerably more nuanced than previously assumed. While earlier models often posited a direct, nearly linear connection, the GFZ study shows that the dynamics beneath the Campi Flegrei have evolved in a far more complex manner. Particularly striking is the change observed since around 2005. According to the researchers, seismic activity has accelerated more rapidly since that point than the measured uplift rate alone could explain. The earthquakes are thus not occurring in proportion to ground uplift; instead, they are responding to subsurface processes in an increasingly nonlinear fashion. From this, the researchers infer that additional physical mechanisms are playing a decisive role.
The Kaiser Effect from rock mechanics
One explanatory framework that has frequently been invoked is the so-called Kaiser Effect from rock mechanics. This model describes how materials respond to repeated loading and, under certain conditions, "store" prior stresses. For understanding the region's long-term development, this concept continues to provide important insights. At the same time, the GFZ study makes clear that this approach alone is not sufficient to explain today's dynamics with precision. Instead, the analysis draws on an expanded physical model that also accounts for time-dependent friction processes along rock fractures. This so-called rate-and-state model allows the researchers to map the observed acceleration of seismic activity considerably more accurately and to explain the developments of recent years in a more consistent manner.
Phases of numerous smaller tremors
Another central finding concerns the so-called earthquake swarms, meaning phases of numerous smaller tremors occurring within a short period. The study shows that these events are not linked to ground uplift to the same degree as the long-term trend. While the general development of seismicity correlates closely with uplift, earthquake swarms apparently follow their own mechanisms. As a possible cause, the researchers point to the intrusion of fluids, such as gases or liquids, into deeper rock layers. These processes can alter the stress conditions in the subsurface over short periods, thereby triggering elevated seismic activity independently of large-scale uplift. The result is a two-part system: a long-term trend shaped by uplift and short-term events triggered by fluid migration.
The Campi Flegrei as a volcanic risk zone
For the region around Naples , these findings are of considerable significance. The Campi Flegrei are considered one of the largest volcanic risk zones in Europe, an area characterized by high population density . A better understanding of the underlying processes is therefore essential for assessing developments realistically and evaluating risks on a more solid basis. The GFZ study shows that the complex dynamics beneath the Campi Flegrei are becoming increasingly amenable to modeling. While many questions remain open, it provides a substantially more precise foundation for distinguishing between long-term trends and short-term events, and for assessing the region's geological activity in a more informed way.