Abstract-This paper presents a least squares (LS) approach for the retrieval of a temporal deformation sequence from a set of interferometric synthetic aperture radar images. The method uses a database of interferograms spanning different long-and short-term intervals, and by solving all the deformations as a unique LS problem provides a chronologically ordered sequence, i.e., a picture of the development of the deformation pattern in time. The approach is illustrated in detail and discussed with respect to both the results of its application on a case study and to possible alternative methods.Index Terms-Ground displacements, least squares methods, synthetic aperture radar (SAR) interferometry.
Abstract. Satellite radar interferometry of Campi Flegrei caldera, Italy, reveals a pattern of subsidence during the period !993-!998. !nterferograms spanning the 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 of a slowing down or reversal of subsidence during the first half of the observation 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 38 _+ 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 pairs of ascending and descending differential interferograms spanning similar time intervals (first half, second half, or entire interval) of the period 1993-1998. In each case the joint inversion fits the two unwrapped interferograms with a similar subhorizontal rectangular contracting tensile dislocation striking roughly N98øE with dimensions -4 x 2 km and located beneath the city of Pozzuoli at a depth of 2.5-3 km. Inversion for 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 possible 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 diffusion as the primary deformation mechanism during this phase of caldera deflation.
Abstract-Anthropogenic features show up as highly coherent objects even in heavily decorrelated interferograms. In order to assess whether the information from such features is still usable, the stability of their phase and coherence is analyzed through a series of interferograms. The results indicate that these features can remain interferometrically stable over several years.Index Terms-Coherence, differential SAR interferometry, man-made features.
S U M M A R YFrom a joint analysis of GPS and InSAR data we have determined the kinematic coseismic surface deformation of the 1999 August 17, Izmit (Turkey) earthquake in terms of strain, rotation and fault slip. The fault slip contribution shows two distinct peaks: one of ∼4 m of slip at Gölcük, and a second of ∼2.9 m slip near Sapanca Lake. The strain field portrays four distinct quadrants reflecting the earthquake focal mechanism. The transition between the quadrants is not centred on the epicentre of the event, but shifted eastwards north of the fault and westwards south of the fault. This shift is the result of a two-stage source rupture process caused by the step-over features in the fault geometry. This rupture process also induced a distinct asymmetry in the displacement field across the fault. We obtain left-lateral shear strains along the Sakarya segment that is the result of a subsequent source nucleating at the Akyazi Gap inducing failure on the easternmost segments. Strong interaction is also observed from a consecutive source near Hersek. Finally, we deduce that the Izmit earthquake has released most of the strain that has accumulated since the last main event on this stretch of the North Anatolian fault in 1719.
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