GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 1.1 71 limited in time, ii) macroseismic fields are inherently incomplete because lacking the offshore areas, iii) intensity data points tend to be strongly clustered along the coast or in the major valleys, therefore iv) site effects might be the controlling factor, due to loose sediments and shallow water table, and v) dynamic parameters of engineering structures and building codes significantly changed in the last 30-40 years. As a matter of fact, the introduction of the Environmental Seismic Intensity scale (ESI-07; Michetti et al., 2007; Serva et al. , 2016) provides nowadays a tool addressing these issues and yielding improved intensity metrics. The distribution of Earthquake Environmental Effects (EEEs) is not dependent on settlements location, and environmental response to large earthquakes is stable over extensive time windows. Starting on the day after the mainshock, we mapped in the field and compiled all the available observations on earthquake environmental effects (EEEs) caused by the Mw7.8 subduction earthquake that hit the coastal region of Ecuador on 16 April 2016 (Pedernales earthquake). These effects include: i) permanent ground deformation, ii) open cracks, iii) liquefaction, iv) landslides, and v) tsunami waves. We use these observations to evaluate the macroseismic field of the Environmental Seismic Intensity - ESI-07 scale and compare our results with published macroseismic data collected using traditional, damage-based, intensity scales. Methods. We grouped the 298 ESI-07 intensity sites into intensity data points (IDPs) taking into consideration local geomorphological settings. Next, we draw isoseismal maps based on visual interpolation of the intensity data points. For traditional intensity data collection (i.e., EMS-98 and MM scales), we used mainly the information provided by Geophysical Institute of Ecuador (IGEPN), which includes an intensity map. Fig. 1 - Location maps and seismotectonic setting; a) regional view of South America, stars indicate the epicenters of large subduction events analyzed in this study, b) subduction segmentation and tectonic setting of Ecuador and nearby regions: small stars are the epicenters of large subduction events; big star is the epicenter of the 16 April 2016, Mw 7.8 Pedernales earthquake; c) epicenter, focal solution and aftershocks of the 2016 Pedernales earthquake.