Regional macroseismic field and intensity residuals of the August 24, 2016, Mw= 6.0 central Italy earthquake

A macroseismic investigation of the August 24, 2016, Mw=6.0 Central Italy earthquake, was carried out
through an online web survey. Data were collected through a macroseismic questionnaire available at the
website www.haisentitoilterremoto.it, managed by the Istituto Nazionale di Geofisica e Vulcanologia
(INGV). Over 12000 questionnaires were compiled soon after the seismic occurrence, coming from over
2600 municipalities. A statistical analysis was applied tothe data collected in order to investigate the spatial distribution of intensity of the earthquake. The macroseismic intensity field (I) was described by identifying three main components: an isotropic component (I
I
), a regional anisotropic component (I
A
) and a
local random variations parameter (ε). The anisotropic component highlighted specific and well-defined
geographical areas of amplification and attenuation. In general, the area between the Adriatic coast and
Apennines Chain was characterized by an amplification ofintensity, while the West side of the Apennines
showed attenuation, in agreement with the domains foundby other works focused on the analysis of instrumental data. Moreover, the regional macroseismic field showed similarities with instrumental PGA
data. The results of our analysis confirm the reliability of web questionnaire data.