In the last 10 years the phenomenon known bradyseism in the Campi Flegrei (CF), has been active, with different earthquakes swarms. This continuous low-magnitude seismic activity, has created problems in the densely populated area of CF, which includes the western portion of Naples. The seismic activity is accompanied by uprising of soils (about 2 cm/month). Some researchers are creating panic in the citizenry as they make hypothesis about the fact that a potential, catastrophic, Plinian eruption might occur any time. Such catastrophists hypothesize that bradyseism occurs due to up-rising of magma. The fact is that there is no proofs or evidence of such magma rising to explain the bradyseism phenomenon. With an international research group [1, and ref therein] we have made an interpretation of the bradyseism which occurs cyclically in the CF, at least in the last 4.000 years, never producing a catastrophic eruption. The only exception was the very small Monte Nuovo phreatic eruption of 1538 AD.

We obtained data during long-term monitoring of the CF volcanic district which has led to the development of a model based on lithological-structural and stratigraphic features that produce anisotropic and heterogeneous permeability features showing large variations both horizontally and vertically. These data are inconsistent with a model in which bradyseism is driven exclusively by shallow magmatic intrusions. Instead, CF bradyseism events are driven by cyclical magmatic-hydrothermal activity. Bradyseism events are characterized by cyclical, constant invariant signals repeating over time, such as area deformation along with a spatially well-defined seismogenic volume. These similarities have been defined as “bradyseism signatures” that allow us to relate the bradyseism with impending eruption precursors. Bradyseism is governed by an impermeable shallow layer (B-layer known as pozzolana), which is the cap of an anticlinal geological structure culminating at Pozzuoli, where maximum uplift is recorded. This B-layer acts as a throttling valve between the upper aquifer and the deeper hydrothermal system that experiences short (1-10² yr) timescale fluctuations between lithostatic/hydrostatic pressure. The hydrothermal system also communicates episodically with a cooling and quasi-steady-state long timescale (10³-10⁴ yr) magmatic system (at depth of 8 km) enclosed by an impermeable carapace (A layer).

Connectivity between hydrostatic and lithostatic reservoirs is episodically turned on and off causing alternatively subsidence (when the systems are connected) or uplift (when they are disconnected), depending on whether permeability by fractures is established or not. Earthquake swarms are the manifestation of hydrofracturing which allows fluid expansion; this same process promotes silica precipitation (and sulphides) that seals cracks and serves to isolate the two reservoirs.

Faults and fractures promote outgassing and reduce the vertical uplift rate depending on fluid pressure gradients and spatial and temporal variations in the permeability field. The mini-uplift episodes also show “bradyseism signatures” and are well explained in the context of the short timescale process.

This interpretation is supported by the fact that earthquake hypocenters at CF are never registered at depths between 4 and 8 km. 90% of the earthquake hypocenters (with M mostly between 1 and 2.5) occur at depths between 1.5 to 3.5 km. We know from deep boreholes that in the CF, that the B-layer; known as “pozzolana” is occurring at depth between 2-3 km [2]. The hydrothermal fluids, fracturing the impermeable layer, pass from lithostatic to hydrostatic pressure; hence they boil, depositing different sulphide mineralizations (pyrite, chalcopyrite, galena, scheelite and others) along the fractured system in the pozzolana B-layer [3-4]. When this occurs, the negative bradyseism begins, and the soil starts to go down slowly.

With the present state-of-the art knowledge of bradyseism, there is no evidence that a catastrophic plinian eruption might occur. Nevertheless millions of people are scared by the phenomenon. What should the Government do? 1. Proceed and prepare for a worst-case potential scenario as a precaution. As there is not evidence of any magma rising up at the moment, create ample, escape roads from which at least 1 million people should be able to escape quickly from the Red Zone of CF; 2. Establish an international panel of researchers and experts to advise the Government and citizenry of CF about seismic activity; 3. Carry out seismological screening of old houses in the Red Zone of CF and identify those not properly built to withstand the continuous small magnitude earthquakes continuously occurring in the Red Zone of CF.