Fewer earthquakes in recent months do not mean the forces driving bradyseism at Campi Flegrei have weakened. That is the assessment given by Lucia Pappalardo, director of the Osservatorio Vesuviano, who said the decline in seismicity does not coincide with a reduction in the processes feeding ground uplift.

Ground uplift, geochemical indicators and pressurisation in the hydrothermal system remain significant, even during a quieter seismic period.

September quieter after the July swarm

In September, 92 earthquakes were recorded in the Campi Flegrei area, with a maximum duration magnitude of 2.0. The lower monthly total followed the energetic seismic swarm of 31 July.

That swarm included a magnitude Md 4.7 earthquake recorded by INGV on 31 July 2026 at 19:46:43 Italian time, at a depth of 3 km. INGV reported its location at 40.8315, 14.1402.

The contrast between July and September illustrates Pappalardo's central point: a reduction in earthquake frequency alone cannot be interpreted as a reduction in the overall activity of the caldera.

Ground continues to rise

The average ground-uplift rate was reported at approximately 10 plus or minus 3 millimetres per month and had not significantly declined after the 31 July earthquake.

Because the bradyseismic process was continuing, the ongoing uplift meant that conditions capable of producing further seismicity remained. In other words, the ground was still moving upward, preserving the potential for more earthquakes even while counts were low.

INGV explains that ground deformation and seismicity are related but do not have a one-to-one relationship over different timescales. Periods with few earthquakes can therefore occur while the ground continues to rise.

Hydrothermal system still active

The monitored geochemical parameters remained within long-term trends associated with heating of the hydrothermal system, pressurisation and elevated fluid fluxes.

That evidence is why Pappalardo distinguished seismic quiet from caldera quiet. Earthquake numbers describe one monitored signal; temperature, gas, fluids and deformation describe others. When those other signals remain elevated, the underlying bradyseismic phase has not ended.

Why INGV watches several signals at once

INGV uses a multiparametric approach combining seismicity, ground deformation, geochemistry and other monitoring data.

For readers, this helps explain why scientists may sound cautious when earthquake numbers fall. A single indicator moving down does not outweigh stable or elevated indicators elsewhere. Assessment depends on the pattern across all monitored parameters, not on seismic counts alone.

What remains uncertain

Earthquakes cannot be predicted, so the available monitoring data cannot establish whether a stronger event will occur in the following weeks.

The available sources also do not establish whether seismicity will increase, decrease or remain stable in the coming weeks, nor do they provide a definitive forecast for when the current bradyseismic phase will end.

The reported magnitude, depth and coordinates of the 31 July event may also be revised as additional information becomes available.