GNGTS 2013 - Atti del 32° Convegno Nazionale

It is today accepted that the seismic cycle can be subdivided in three main different phases: interseismic, coseismic and postseismic (e.g. Scholz and Kato, 1978). Actually, the interseismic phase can be again subdivided into a purely interseismic step and a preseismic one, but the state of knowledge concerning the latter is still vague (e.g. Deng et al. , 1998). The post-seismic deformation occurs soon after the seismic event and it can be subdivided in two phases, characterized by short and long-term deformation. The short-term deformation can usually be attributed to afterslip and/or pore pressure readjustments, which take place over periods ranging from a few hours to a few months after the earthquake. Deformation cannot be accurately measured by interferometric methodologies if the image sampling interval over the area is too long (several days or months).The long- term postseismic deformation is instead related to the viscoelastic relaxation that occurs in the lower crust and upper mantle, following several months or years (depending on the magnitude) after the earthquake (e.g. Segall, 2002). This kind of deformation, also called viscoelastic rebound, is difficult to be isolated using InSAR data, because: a) it is often characterized by ground velocities at the lower boundary of the InSAR measurement capability (<1 mm/yr); b) is spread over long distances and can be confused with long-wavelength InSAR error sources as well as with interseismic deformation. In this work we do not consider crustal deformation caused by the viscoelastic rebound because of the small magnitude of the considered earthquakes and the small length of the data time- series; we focus our attention on the interseismic, coseismic and postseismic (afterslip and/or pore pressure readjustments) phases. From the geological point of view the earthquake cycle reveals itself through field evidence, such as abrupt offsets or diffuse deformation of lithological reference layers, fluvial or marine terraces, depositional or erosional landforms, faults escarpments, etc. The seismic cycle and the fault activity are also studied using paleo-seismological trenches, where geologists can measure and date stratigraphic layers to evaluate long term averages of strain rates and displacements. Starting from geological or paleoseismological field data, it is possible to evaluate the mean slip rate along a fault, and recognize the main seismic events (those which have ruptured the surface); these slip rates are usually averaged over a time span of thousands or tens of thousands of years (Pantosti et al. , 1993). To study the seismic cycle in the long term (interseismic phase), we need to integrate geological and geodetic data, which entails integrating slip rates averaged over many seismic cycles, and present day ground velocity maps. To reconcile these different data we need to identify the sources responsible for the present day strain accumulation (and geodetic velocity), and possibly know the long term slip rate along them. In this way we can compare the geologic and the geodetic slip rates. The geodetic slip rate can only be obtained by appropriate modeling of the geodetic data; normal methods for interseismic geodetic data inversion neglect transient deformation processes and estimate slip rates by assuming slip on a fault to occur by steady creep only below a locking depth, in an elastic half-space, over the course of the earthquake cycle. On the other hand, for short-term studies of the earthquake cycle (co and post seismic phases), is very important to understand and identify the seismic sources and the interaction between each other. In fact, during a seismic crisis, typically several different data are available to the researchers concerning the hypocenters, preexisting geological and ad hoc field data, cinematic of the sources, magnitudes, punctual displacement data (GPS) and displacement fields (SAR); one of the main goals is to reconcile all of these data to define the seismic sources (geometries, kinematics and locations) and to investigate the relationship between the main sources and the static stress variations along the modeled fault planes (e.g. Pezzo et al. , 2013). In this work, we present the results of the multitemporal InSAR-SBAS analysis (Berardino et al. , 2002) for the measurement of low interseismic ground velocities, in particular we study the interseismic deformation in the Gargano promontory (Southern Italy) and in the Doruneh region (Northern Iran) (Pezzo et al. , 2012). In both cases we focused our attention (i.e. the modeling) on the most prominent tectonic structures of the areas, the Mattinata Fault, for the 94 GNGTS 2013 S essione 1.1