Locating distributed faulting: Contributions from InSAR imaging to Probabilistic Fault Displacement Hazard Analysis (PFDHA)

Prediction of location and amount of slip for distributed faulting associated to strong earthquakes is a recently explored issue with major implications in terms of hazard assessment. Currently, the best practice involves the applications of Probabilistic Fault Displacement Hazard Analysis (PFDHA) whose results fit sufficiently well real data in the near-range of the primary fault but show considerable inaccuracies in the far-range.We believe that this inaccuracy descends from the biased earthquake databases used for regression analysis, whose data, relative to old earthquakes, were largely collected only by field surveys focused close to the primary fault (i.e., near-range). Remotely-sensed data (i.e., Interferometric Radar Imaging e InSAR) offer the opportunity to precisely measure the surface deformation induced by strong earthquakes and thus to explore its possible relation with distributed faulting. We analyze the L'Aquila earthquake case study (29th April, 2009, Mw 6.3) and explore the correlation between location and slip on distributed faulting and InSAR-derived deformation field.We find a significant correlation between occurrence of distributed faulting and profile curvature of the dislocation field, in spite of the distance from the primary fault. Moreover, distributed faults tend to occur within the area deformed by the earthquake, as imaged by InSAR data and whose extent is directly proportional to the earthquake magnitude (Mw), according to a dataset of 30 recent earthquakes. We then propose that these observations have to be incorporated into the present PFDHA practice as limit boundaries to possible scenarios of probabilistic analysis and that an integrated use of field-based and remotely data collection have to be implemented, following strong earthquakes.