Hot-Cold Spots in Italian Macroseismic Data

TL;DR

This paper investigates anomalous hot and cold spots in Italian macroseismic data, attributing them to local fault geometry rather than soil conditions, with implications for seismic hazard analysis.

Contribution

It identifies and catalogs sites with unexpected seismic amplification or reduction linked to fault geometry, expanding understanding beyond traditional site effects.

Findings

Certain sites show amplification or reduction unrelated to soil conditions.

Anomalous sites can cluster at various scales.

Some sites exhibit opposite effects depending on the earthquake.

Abstract

The site effect is usually associated with local geological conditions, which increase or decrease the level of shaking compared with standard attenuation relations. We made an attempt to see in the macroseismic data of Italy some other effects, namely, hot/cold spots in the terminology of Olsen (2000), which are related to local fault geometry rather than to soil conditions. We give a list of towns and villages liable to amplify (+) or to reduce (-) the level of shaking in comparison with the nearby settlements. Relief and soil conditions cannot always account for the anomalous sites. Further, there are sites where both (+) and (-) effects are observed depending on the earthquake. The opposite effects can be generated by events from the same seismotectonic zone and along the same direction to the site. Anomalous sites may group themselves into clusters of different scales. All isolated anomalous patterns presented in this paper can be used in hazard analysis, in particular, for the modeling and testing of seismic effects.