Characterization of the co-seismic slip field for large earthquakes

Focused studies on large earthquakes have highlighted that ruptures on generating faults are strongly heterogeneous. The main aim of this thesis is to explore characteristic patterns of the slip distribution of large earthquakes, by using the finite-fault models (FFM) obtained in the last 25 years. A result of this thesis is the computation of regression laws linking focal parameters with magnitude. Particular attention was devoted to the aspect ratio (A.R.), defined as the ratio between fault length and width. FFMs have been partitioned in 3 A.R. classes and for each class, the position of the hypocentre, of the maximum slip and their mutual relation were investigated. To favour inter-comparison, normalised images of on-fault seismic slip were produced on geometries typical of each A.R. class with the goal of finding possible regularities of the slip distribution shapes. In this thesis, the shape of the single-asperity FFMs has been fitted by means of 2D Gaussian distributions. To the knowledge of the author, this thesis is the first example of a systematic study of finite-fault solutions to identify the main pattern of the on-fault co-seismic slip of large earthquakes. One of the foreseen applications is related to tsunamigenesis. It is known that tsunamis are mainly determined by the vertical displacement of the seafloor induced by large submarine earthquakes. In this thesis, the near-source vertical-displacement fields produced by the FFM (assumed as the real one), by a homogeneous fault model, by a depth-heterogeneous fault model and by two distinct 2D Gaussian distribution fault models were computed and compared for all single-asperity earthquakes. The main finding is that 2D Gaussian distributions give the least misfit fields and are therefore the most adequate for tsunami generation modelling.