GNGTS 2017 - 36° Convegno Nazionale

222 GNGTS 2017 S essione 2.1 Sigbjörnsson R., Zonno G., Oliveria C.S.; 2016: Foreword to the special issue: the European project UPStrat-MAFA (Urban disaster prevention strategies using MAcroseismic Fields and FAult Sources) . Bulletin of Earthquake Engineering, 14 , 1773-1776, doi: 10.1007/s10518-016-9924-5. Zonno G., Rotondi R., Brambilla, C; 2009: Mining macroseismic fields to estimate the probability distribution of the intensity at site . �������� �� ��� ������������� ������� �� �������� Bulletin of the Seismological Society of America, 95 (5), 2876-2892. Heterogeneous slip distribution on faults responsible for large earthquakes: characterization and implications for tsunami modelling E. Baglione, A. Armigliato, S. Tinti Dipartimento di Fisica e Astronomia (DIFA), Alma Mater Studiorum-Università di Bologna, Italy The fact that ruptures on the generating faults of large earthquakes are strongly heterogeneous has been demonstrated over the last few decades by a large number of studies. The on-fault slip tends to concentrate in “patches” over the fault surface, whose number, dimension and relative position is highly variable. Two clear examples of this variability are provided by the Sumatra- Andaman earthquake of 26 December 2004 (Mw=9.1) and the Tohoku earthquake of 11 March 2011 (Mw=9.0) (e.g., Geist et al. , 2007; Løvholt et al. , 2012; Goda et al. , 2014). The slip heterogeneity has immediate consequences on the seismic radiation field as well as on the permanent (co-seismic) deformation of the Earth’s crust, that are very likely to differ significantly from what would be expected on the basis of a simple uniform slip. This can reflect also on other hazardous phenomena directly triggered by earthquakes, such as tsunamis, as clearly demonstrated by the above mentioned 2004 and 2011 events. In the case of earthquake-induced tsunamis, the generating mechanism is represented by the co-seismic vertical displacement of the seafloor, whose pattern is clearly dependent on the on-fault slip distribution at depth. If we take the case of the Mediterranean, where the tsunamigenic sources are often located a few/few tens of kilometres away from the coast, the effect of the slip heterogeneity in determining the tsunami wave propagation features and the run-up distribution along the coasts is critical. Finite-Fault Models (FFMs), i.e., the matrix representations of the slip values on the fault surface, are generally retrieved through the inversion of different types of data (seismic, geodetic, tsunami-related), taken individually or simultaneously. The development and refinement of proper inversion algorithms have been a prolific research field at least in the last decade, and it has been accompanied in the last years by the systematic collection and format homogenisation of the published/proposed FFMs for different earthquakes in specifically conceived databases, such as SRCMOD (����������������������������� � �� �������� ����������� ���� ��� ���� http://equake-rc.info/SRCMOD ). At present, preliminary FFMs are made available some tens of minutes to few hours after the occurrence of large-magnitude events. Refined FFMs take much longer times. The main aim of this study is to explore characteristic patterns of the slip distribution of large earthquakes, by using a subset of the FFMs contained in SRCMOD, covering events with moment magnitude equal or larger than 6 and occurred worldwide over the last 25 years. The possibility to recognise characteristic slip patterns can have relevant consequences both on the long-term hazard assessment and on the real-time warning in the near-field, not only for the seismic part, but also for tsunamis in case of the occurrence of large-magnitude offshore earthquakes. We focus on those FFMs that exhibit a single and clear region of high slip (i.e., a single asperity), which is found to represent the majority of the events. For these FFMs, it sounds reasonable to best-fit the slip models by means of 2D Gaussian Distributions (GD). Two