###### Abstract
In addition, the incorrect assessment of seismic vulnerability could significantly affect the assessment of cumulative damage after the main shock of each seismic sequence. Consequently, there may be significant problems in assigning seismic intensity for earthquake events in the catalog. The correct definition of the seismic vulnerability of buildings for events in the historical catalog is an extremely complex problem; this topic is beyond the scope of the present study but is an important topic of study for our research group. Up to now, source parameters, i.e., fault surface projection and macroseismic magnitude expressed as M\({}_{\rm w}\) proxy (M\({}_{\rm wp}\)), in Italy are generally recovered using a method shown in [6; 7], which is known as \"boxer\". It has been widely used by other investigators aside from the main authors [8; 9]. It assumes that the fault surface projection corresponds to that of the area of maximum intensities. As it can be understood, it is extremely rough, since often the fault is shifted to the side of the main area of damage but allows for a wide application even in cases where relatively few intensity points are available. To better understand the problem, in Figure 1, we show two cases in Italy where the source is markedly shifted with respect to the area of main damage. In Figure 1a, the case of the M\({}_{\rm w}\)6.45 on 6 May 1976 is depicted. A summary of the hypotheses of sources for 1976 is reported in [10], where the more accredited sources are distributed in the Gomon area. One of the older ones is [11], evaluated by [12; 13; 14]. In blue is shown the area involving the largest asperities of the 6 May 1976 M\({}_{\rm w}\)6.45 Friuli earthquake [15]--slightly NE to the area in [14] and similarly, we show the area of main deformation of the 20 May 2012 M\({}_{\rm w}\)6.09 Mirandola earthquake [16]. Incidentally, the Friuli earthquake occurred in the same area as the 1928 event, which is the one investigated in this paper. Figure 1: **(a)** Macroseismic field of the 6 May 1976 event (CPTI15) [1,2]. Blue polygons are the surface projection of the two main asperities, as modeled in [10]. **(b)** Macroseismic field of the 20 May 2012 event (CPTI15) [1,2]. The blue polygon is the surface projection of main asperity, as modeled in [16]. The 2012 event occurred in the Po plain (Figure 1b) and, contrary to the usual expectation of strong amplification in such an environment, the macroseismic field yields a macroseismic magnitude of M\({}_{\rm wp}\)5.15. The nearby Po River had probably saturated the terrain sediments that compose the upper layers of the plain over a thickness of several kilometers, effectively attenuating the S-waves. In contrast to the case of the 1976 alluvial fan, it was observed that at the transition from the lower to the upper part of the fan--and thus at greater thickness--the intensity increases by up to three degrees, which represents a very large difference in international case history [10]. In this paper, we further develop the KF method in order to make it more widely applicable to as many historical macroseismic fields as possible. The obvious conclusion is that we cannot obtain a totally unconstrained source solution because often the degrees of freedom yielded by the macroseismic field are less than those required by the KF source description method that in turn is already a simplified version of the true one. This is because a macroseismic field described in terms of MCS provides at most 11 possible values and quite often even less, much less, than that. We want to clarify here that the CPTI15 strictly abides to the quantization of intensity values. Even whenever two intensities are given (e.g., M\({}_{\rm MCS}\) = 7-8), it means that there is an uncertainty between the two values, but the quantization still holds. As a showcase for our theoretical development, we choose an M\({}_{\rm wp}\)6 event that occurred in Northeastern Italy in 1928.