17 Feb 2022
17 Feb 2022
Status: a revised version of this preprint is currently under review for the journal NHESS.

Modern earthquakes as a key to understanding those of the past: the intensity attenuation curve speaks about earthquake depth and magnitude

Paola Sbarra, Pierfrancesco Burrato, Valerio De Rubeis, Patrizia Tosi, Gianluca Valensise, Roberto Vallone, and Paola Vannoli Paola Sbarra et al.
  • Istituto Nazionale di Geofisica e Vulcanologia (INGV), Via di Vigna Murata 605, 00143 Rome (RM), Italy

Abstract. The Italian historical earthquake record is among the richest worldwide; as such it allows the development of advanced techniques for retrieving quantitative information by calibration with recent earthquakes. Building on a pilot elaboration of northern Italy earthquakes, we developed a procedure for determining the focal depth of all Italian earthquakes from intensity data alone. In a second step the procedure calculates their magnitude, taking into account the inferred depth.

Focal depth exhibits a substantial variability countrywide, but so far received little attention: pre-instrumental earthquakes were routinely "flattened" at upper crustal level (~10 km), on the grounds that the calculation of focal depth is heavily dependent on the largely unknown local propagation properties.

We gathered a learning set of 42 earthquakes documented by reliable instrumental data and by numerous intensity observations. Rather unexpectedly we observe (1) that within 50 km from the epicenter the ground motion attenuation rate is primarily controlled by focal depth and largely independent of magnitude; (2) that within this distance the fluctuations of crustal attenuation properties are negligible countrywide; and (3) that knowing both the depth and the expected epicentral intensity makes it possible to estimate a reliable magnitude.

Paola Sbarra et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on nhess-2022-30', Anonymous Referee #1, 17 Mar 2022
    • AC1: 'Reply on RC1', Paola Sbarra, 23 May 2022
  • RC2: 'Comment on nhess-2022-30', Anonymous Referee #2, 12 Apr 2022
    • AC2: 'Reply on RC2', Paola Sbarra, 23 May 2022

Paola Sbarra et al.

Paola Sbarra et al.


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Short summary
Earthquakes are fundamental for understanding how the Earth works and for assessing seismic risk. We can easily measure the magnitude and depth of todays' earthquakes, but can we do it also for pre-instrumental ones? We did it by analyzing the decay of earthquake effects (on buildings, people, objects) with epicentral distance. Our results may help deriving data that would be impossible to obtain otherwise, for any country where the earthquake history extends for centuries, such as Italy.