Developing the First Intensity Prediction Equation Based on the Environmental Scale Intensity: A Case Study from Strong Normal-Faulting Earthquakes in the Italian Apennines

Abstract

Earthquakes produce effects on the built and natural environment, the severity of which decays with distance from the epicenter. Empirical relations describing the intensity attenuation with distance are fundamental for seismic hazard assessment and for deriving parameters for preinstrumental events. Seismic intensity is usually assigned based on damage to buildings and infrastructures; this can be challenging for intensity degrees higher than X or when macroseismic fields of multiple events close in time are overlapping. A complementary approach is the study of earthquake environmental effects (EEEs), which are used to assign intensity on the environmental scale intensity (ESI) scale. However, a quantitative comparison between the ESI and traditional scales, and an equation describing the ESI attenuation with distance are still lacking. Here, we analyze 14 historical and instrumental events (time window 1688–2016) in the central and southern Apennines (Italy), comparing ESI and Mercalli–Cancani–Sieberg (MCS) intensities. Our results show that ESI consistently provides higher intensity near the epicenter and the attenuation is steeper than MCS. We derive the first intensity prediction equation for the ESI scale, which computes local intensity as a function of distance and epicentral intensity value. We document that, in the near field, the MCS attenuation for shallow crustal events occurred in the twenty-first century is steeper than previous events, whereas the ESI attenuation shows a consistent behavior through time. This result questions the reliability of current empirical relations for the investigation of future events. We recommend including EEEs in intensity assignments because they can guarantee consistency through time and help in evaluating the spatial and temporal evolution of damage progression during seismic sequences, thus ultimately improving seismic risk assessment.

The 2017, MD = 4.0, Casamicciola Earthquake: ESI-07 Scale Evaluation and Implications for the Source Model

“…The spatial distribution of the environmental effects of the earthquake (EEE) and the isoseismal map confirms that the area between Fango (Lacco Ameno) and Piazza Bagni localities (Figures 2 and 5) is the epicentral area. It is important to note that in the epicentral area of damaging earthquakes, when compared with traditional intensity scales the ESI intensity map generally shows a steeper attenuation in the near field (e.g., [27,69]). Therefore, ESI intensity typically provides better constraints on the location and geometry of the seismic source.…”

Assessing the Reliability of Earthquake Environmental Effects in Historical Events: Insights from the Southern Apennines, Italy

“…An ESI macroseismic field was not available for all the earthquakes, so we derived it from an intensity prediction equation (IPE), which expresses the ESI intensity as a function of epicentral intensity I 0 and distance. The equation was developed by the authors of [6] from over 400 ESI intensity data points belonging to 14 earthquakes that occurred in the Central and Southern Apennines; data were binned according to the intensity value, and the median value for each class was used to derive the prediction equation adopting a least-squares approach. A log-linear functional form was selected based on the fitting performance.…”

“…A log-linear functional form was selected based on the fitting performance. The IPE assumed the following values [6]:…”

“…To reach this goal, here we analyze five earthquakes that occurred in the Southern Apennines (Italy) between 1688 and 1980, to assess if EEEs are reliable indicators of the effects caused by past seismic events, that occurred either in the pre-instrumental or instrumental era. We analyze the spatial distribution of EEEs and we quantitatively compare the MCS/MSK fields with an ESI theoretical field derived from a recently published attenuation relation [6].…”

BEGEOSCIENTIST a young network - I Congresso Nazionale dei Giovani Geoscienziati

“…For the EMS-98, maximum intensity is I EMS VIII between Pennisi and Fleri (QUEST WG, 2019), showing disagreement with the ESI-07 data. It is important to note that the intensity of the traditional macroseismic scales might be affected by the introduction of new building codes, resulting in a decrease of macroseismic intensities for earthquakes occurred in the last decade (Ferrario et al, 2020). The collected data allow us to suggest that the ESI-07 works better than traditional macroseismic scale in the seismotectonic environment of Mt.…”