The importance of quantifying uncertainties of macroseismic magnitudes : a methodological comparison of their estimates along the French-Italian border

Ludmila Provost (1) , O. Scotti (1) , Andrea Antonucci (2) , Andrea Rovida (2)

1 IRSN/PSE-ENV/SCAN/BERSSIN - Bureau d'évaluation des risques sismiques pour la sûreté des installations
2 INGV - Istituto Nazionale di Geofisica e Vulcanologia – Sezione di Milano

Magnitude estimates of earthquakes occurred before the instrumental period are a key issue in seismic hazard assessment. Such estimates are based on information provided by historical sources, which is translated into macroseismic intensity by means of intensity scales. Methods for computing earthquake parameters from intensity data differ within and between countries. We compare magnitude estimated from the application of the Boxer (Gasperini et al 2010) and QUake-MD (Provost and Scotti, 2017) methods to a set events located along the French-Italian border. Using the same macroseismic data and epicentral location we find a systematic magnitude (+-/ 0.5) bias for M>5.0 and for M< 4.0. The origin of this bias could be due to differences in the two methodologies, in the set of calibration events used, in their mathematical formulation, and/or in their implementation procedure. We compare the intensity predicted by the two methods with the same magnitude, epicentral intensity and depth, and observe a systematic bias in the intensity prediction in accordance with the magnitude bias mentioned above. The decrease of intensity with epicentral distance is not the same for the two methods, and Boxer overestimate the predicted intensity in comparison with QUake-MD for the highest predicted intensity levels, leading to an overestimation of magnitude by QUake-MD for earthquakes with M>5.0. However when we consider the uncertainties reported in the two methodologies, both magnitude estimates intersect, underlining the importance of quantifying uncertainties in parametric earthquake catalogues and the need to propagate such uncertainties in seismic hazard assessments.

Mots clés: historical earthquake; intensity macroseismic data; Magnitude

Domaines: Planète et Univers [physics]

Ludmila Provost, O. Scotti, Andrea Antonucci, Andrea Rovida. The importance of quantifying uncertainties of macroseismic magnitudes : a methodological comparison of their estimates along the French-Italian border. 27th General Assembly of International Union of Geodesy and Geophysics (IUGG), Jul 2019, Montréal Quebec, Canada. ⟨irsn-04095303⟩