## 4 Discussion  
Two focal mechanisms of the M\({}_{\text{wp}}\)6 27 March 1928 earthquake are available in [49]. This allows for a first validation of the improved version of the KF and the obtained solution (Figure 6). The first positive aspect is that all the three possible macroseismic epicenters are spaced at most 6 km west apart from that in [49]. However, all three of our solutions yield impossibly low dip values. There is, however, an explanation; we need first to compute the isoseisimals with the method proposed in [50]. In our case, isoseisimals are roughly circular. This shape is typical of dip-slip events: we know [21] in this case that dip is often not well constrained and it can yield unrealistically low values. We prefer, therefore, solution S2, even though we trust only strike (the auxiliary plan of S2 = 234\({}^{\circ}\), 81\({}^{\circ}\), 86\({}^{\circ}\), similar to S3) and a rake \(\pm\) 180\({}^{\circ}\). By tectonic considerations, we prefer a rake of 99\({}^{\circ}\). Figure 5: Observed macroseismic field versus modeled one for our preferred mechanism (S3) using 256 intensity points within 100 km. Modeled points have a diameter that is twice as big as the observed points; the central portion of each point therefore refers to the observed data and the outer ring to the modeled point. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Solution** & **Intensity** & **M\({}_{\text{wp}}\)** & **Lat** & **Long** & **Strike** & **Dip** & **Rake** & **Depth** & **Along Strike** & **Antistrike** & **Match** \\ \hline S1 & 0.8477 & 5.99 & 46.34 & 12.95 & 108 & 1 & \(-\)30 & 14.0 & 3.0 & 7.0 & 0.52 \\ S2 & 0.8516 & 5.99 & 46.36 & 12.93 & 63 & 9 & 99 & 14.0 & 1.0 & 9.0 & 0.53 \\ S3 & 0.8543 & 5.99 & 43.36 & 12.93 & 236 & 81 & 89 & 13.0 & 9.0 & 1.0 & 0.53 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Best solution parameters. This solution places the 1928 rupture directly in southern continuation with the But-Chiarso line. At first it may seem odd, but we must remember that where arcs merge, tectonic styles can coexist [51]. We suppose therefore that the solutions proposed by the authors of [52], although not very different from ours, were maybe influenced by an inappropriate depth that led to a strike-slip rupture. A final remark is linked to the relation between the 1928 event and the 1976 event (Figure 7). It is extremely interesting that the 1928 earthquake is placed between the two main asperities ascribed to the 1976 event. Our finding therefore seems to give a powerful indication that when investigating seismic hazards, we should take into account mainly the asperities and not the whole fault. This is deeply intertwined with the open question of what the return times of events are. According to our finding, it would probably be more appropriate to think in terms of return times on asperities, since the rest of the fault might  
Figure 6: The figure shows the isoseisimals of the M\({}_{\rm wp}\)6 27 March 1928 earthquake, interpolated using the natural neighbor method [50]. Figure 7: S1, S2, and S3: best representatives of three families of solutions (only dip and rake are reported); yellow: solutions after [42] (only dip and rake are reported); blue polygons: areas of maximum deformation after [10]; red and orange lines: active thrusts and strike-slip faults, respectively (all dipping toward the labels), after [33]. slip almost passively whenever a previous event occurred in the same volume. Obviously, this is only a first case, and this behavior should be proved or disproved by studying many other possible similar situations. In fact, if we examine all the over 200 macrosemic fields available in the CPTI15 catalog for events with M\({}_{\rm wp}>5.5\), we note that only in two cases we might assume that there is a qualitative similarity between them. Conversely, as a rough estimate, we can affirm that about 80% of the events in the catalog occur within at most 20 km from a previous event.