Modeling surface deformation observed with synthetic aperture radar interferometry at Campi Flegrei caldera

Satellite radar interferometry of Campi Flegrei caldera, Italy, reveals a p attern of subsidence during the period 1993-1998. Interferograms spanning t he first half of the observation period (1993-1995) have a lower amplitude and average rate of subsidence than those spanning either the second half ( 1995-1998) or the entire period (1993-1998), consistent with observations o f a slowing down or reversal of subsidence during the first half of the obs ervation period. We calculate a time series of deformation images relative to a reference image on the basis of a least squares inversion. During the observation period the maximum subsidence progresses at a rate of roughly 3 8 +/- 2 mm/yr, with periods of no apparent subsidence in late 1996 to early 1997. To understand the characteristics of the source, we jointly invert p airs of ascending and descending differential interferograms spanning simil ar time intervals (first half, second half, or entire interval) of the peri od 1993-1998. In each case the joint inversion fits the two unwrapped inter ferograms with a similar subhorizontal rectangular contracting tensile disl ocation striking roughly N98 degreesE with dimensions similar to 4 x 2 km a nd located beneath the city of Pozzuoli at a depth of 2.5-3 km. Inversion f or a spheroidal or Mogi point source also produced reasonable fits but with progressively poorer overall fits to the data, respectively. Our inversion assuming a simple source in an elastic half-space does not include the pos sible effects of local structure on the surface deformation, a factor that may also reduce the need for an asymmetric source. The solution we find is consistent with other studies that suggest subsidence due to hydrothermal d iffusion as the primary deformation mechanism during this phase of caldera deflation.