Analytical expressions for the static displacement field produced by a centre of dilation and by a pressure source in a viscoelastic half-space are derived. The associated stress fields are also computed. The rheology of a standard linear solid (SLS) is adopted for the shear modulus, while the incompressibility is kept elastic. An instantaneous dilation or variation of pressure is considered as responsible for the deformation. In the centre of dilation model, if the two rigidities of the SLS are of the same order of magnitude, the viscoelastic contribution to the deformation is negligible; if the short-term rigidity is at least two orders of magnitude higher than the other one, the results are indistinguishable from those obtained with a Maxwell solid rheology. In this case, it is found that the initial elastic displacement is amplified by 20 per cent. In the pressure source model, if the rigidities of the SLS are of the same order of magnitude, the initial elastic displacement is amplified by a factor of about 2, but unrealistically high pressure values are required. On the other hand, for a Maxwell solid rheology the displacement grows indefinitely in time, following a sudden application of a finite pressure. The uplift rate is evaluated and it is shown that, for obtaining values of the order of 1 m over one characteristic relaxation time, more reasonable values of pressure are allowed. Applications to ground deformation in volcanic areas are discussed, taking as an example the Campi Flegrei zone, near Naples, Italy.

Campi Flegrei (Italy) caldera has experienced episodes of ground deformation throughout its geological history, alternating between uplift and subsidence phases. Although uplift periods are typically more alarming, here we focus on subsidence, looking for its driving mechanisms and its role in the caldera evolution. Historical and archaeological records constrain ground deformation over the last two millennia.Here we revise such records and combine them with published radiometric dating and with the simulation of sea level change. The resulting analysis highlights for the first time a rapid subsidence during the fifth century. We show that rate and magnitude of this subsidence are consistent with the compaction of porous material caused by a pressure drop of~1 MPa within the hydrothermal system. We interpret this event as the decompression of the hydrothermal system following an unrecognized episode of unrest, during Roman times. These findings redefine the pattern of ground deformation and bear important implications for volcanic hazard assessment.

The first stage of the trial in L'Aquila (Italy) ended with a conviction of seven experts, convened by the head of Civil Protection on 31 March 2009, for multiple manslaughter and serious injuries. They were sentenced to six years in jail, perpetual interdiction from public office and a fine of several million euros to be paid to the victims of the earthquake of 6 April 2009 (moment magnitude 6.3) for having caused, by their negligent conduct, the death of 29 persons and the injury of several others. The verdict had a tremendous impact on the scientific community and on the way scientists deliver their expert opinions to decision makers and society. This paper analyses the scientific argumentations reported in the Verdict Motivations, where scientific data and results were largely debated and misused to demonstrate that they should have been considered as a tool to predict an impending large earthquake. Moreover, we show that the supposed message of reassurance was not generated at the experts' meeting or by the official Istituto Nazionale di Geofisica e Vulcanologia reports. The media had a key role in conveying information during the seismic swarm, contributing to the risk perception. We stress that prevention actions based on seismic hazard knowledge are the best defence against earthquakes.'incomplete, imprecise and contradictory information on nature, causes, hazard and future development of the seismic activity, neglecting thus their duties to evaluate the connected risks and the function of forecasting, prevention and delivery of clear, correct and complete information'.

We have studied single‐mode mean field equations associated with variable viscosity convection for both steady state and time‐dependent situations. Steady state mean field solutions can be obtained by treating the governing mean field equations as two coupled fourth‐order differential systems, which are solved as a series of coupled two‐point boundary value problems with underrelaxation. Steady solutions can be achieved in which there can exist viscosity contrasts exceeding 108 and interior Rayleigh numbers of 0(109). For comparison with two‐dimensional solutions we have employed results derived from two finite element methods. Both temperature‐dependent and temperature‐ and pressure‐dependent viscosity with the surface viscosity fixed have been studied. Our results show that the differences between the two approaches grow with both viscosity contrast and convective vigor. The steady state Nusselt numbers and interior temperatures are greater in the case of mean field solutions. The power law index β governing the relationship between the interior Rayleigh number and the Nusselt number is larger for the mean field. Comparison of time‐dependent solutions shows that one can monitor rather faithfully the evolution of the averaged interior temperature and surface heat flow over a long time scale with the mean field method. Initially, thermal instabilities originating from the mean field boundary layers are found to be correlated with two‐dimensional boundary layer instabilities and are much more violent in character and cause large oscillations of the surface heat flow. The time scales associated with the secular variations of the Urey number, representing the ratio of the heat production and the surface heat loss, agree well between the two approaches. These results suggest that the mean field equations may serve as an efficient vehicle for studying planetary convection with complicated physics.

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