Quantification of earthquake diagnostic effects to assess low macroseismic intensities
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Quantification of earthquake diagnostic effects to assess low macroseismic intensities Paola Sbarra1 · Patrizia Tosi1 · Valerio De Rubeis1 · Diego Sorrentino1 Received: 9 April 2020 / Accepted: 21 August 2020 © The Author(s) 2020
Abstract A large amount of data about earthquake effects, supplied by citizens through a web-based questionnaire, enabled the analysis of the occurrence of many of the effects on humans and objects listed in macroseismic scales descriptions. Regarding the other diagnostic effects (rattling, moving, shifting, falling or overturning depending of the object type of doors, windows, china, glasses, small objects, pictures, vases, books, as well as frightened people and animal behaviour), data from more than 300,000 questionnaires about earthquakes felt in Italy from June 2007 to August 2017, were analysed by stacking them together as a function of hypocentral distance and magnitude. The comparison of the resulting percentages with the intensity prediction equation showed that almost all the chosen effects are good diagnostics for macroseismic intensity evaluation, as their percentages are well differentiated. We did not analyse the oscillations of hanging objects and liquids because the differences in effect attenuations, highlighted by the maps of the occurrence percentage, suggested to not consider them as diagnostic effect. This result allowed us to quantify the occurrence of each diagnostic effect for the intensity degrees from II to VI of the European macroseismic scale for the people who felt the earthquake. The application of the intensity assessment method to internet macroseismic data, based on the specifications herein proposed, should mitigate the problem of “not felt” undersampling in crowdsourced web data. Keywords Diagnostic effects · EMS scale · Macroseismic questionnaire · Intensity estimation · Earthquake
1 Introduction Macroseismic scales are based on experimental observations that are categorised to obtain the estimation of intensity levels of ground shaking. Objects and buildings can be considered as “instruments” in recording seismic effects, and even human response to ground shaking, when averaged over a large number of samples, can be a good indicator of the level of ground motion (Kayano 1990; Dengler and Dewey 1998). The descriptions of macroseismic scales detail an increase in the level of intensity of each diagnostic effect * Paola Sbarra [email protected] 1
Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, 00143 Rome, Italy
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observed. As stated in the European macroseismic scale (EMS, Grünthal 1998), “The scale recognises the statistical nature of intensity, that is, that at any place a certain effect is likely to be observed in a proportion of cases only, and whether that proportion is small or large is itself something that tells one about the strength of the shaking.” These trends, based mainly on reports from the field, but even on common sense, have been studied systematically in large
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