Geological Surveys of Italy and China confirm the relevance of ESI 2007 intensity scale to evaluate the earthquake effects on natural environment

The Italian territory is characterized by a geological and geomorphological complexity associated to several types of hazards (earthquakes, volcanoes, landslides, etc.) that need to be properly evaluated and carefully considered in the frame of land planning. These procedures has to be based on an update knowledge of the effects produced by such hazards on the natural environment.

Experts from the Geological Survey of Italy (ISPRA) and China (CGS) have cooperated in testing and validating the seismic intensity scale ESI 2007 in areas characterized by different tectonic context and by different site conditions (geomorphologic, lithologic and climatic).

The ESI 2007 (Environmental Seismic Intensity Scale) is an intensity scale based only on the effects produced by earthquales on the natural environment. It was proposed by a group of geologists and seismologists with the perspective to evaluate the impact of an earthquake especially in the areas where tha lack of buildings does not allow a traditional intensity assessment based on damages.

The ESI 2007 scale classifies environmental effects into 12 intensity degrees: primary effects are surface faulting (whene a fault rupture displaces the topographic surface), but also tectonic uplift and subsidence. Secondary effets are liquefactions, ground cracks, landslides, hydrological variations and tsunamis.

By using the ESI 2007 scale, experts from ISPRA and CGS have compared the geological effects induced by three strong earthquake that hit the Sichuan region (China) in 2008, 2013 and 2017, with three earthquakes occurred in the same period in Central Apennines, 2009, 2016 Aug. 24; 2016 Oct. 30).

This comparison has confirmed that in general the size and areal distribution of environmental effects is proportional the earthquake severity. However, for moderate earthquakes (magnitude between 6 and 7), surface faulting was observed only in extensional domains (Central Apennines) while in compressive domains (Sichuan) surface faulting was observed only for the stronger event (Wenchuan, magnitude about 8). Moreover, it was evidente a key role played by site conditions (e.g. local lithology, elevation, sloping, soil thickness, climatic conditions) in the occurrence of secondary effects, like landslides.

The comparison with traditional intensities based on damages has confirmed the crucial role played by ESI scale in depicting the earthquake effects scenario and to point out the most hazardous areas, especially those characterized by slope instability and occurrence of liquefaction phenomena.

For further information, we suggest to look at a scientific paper published on Engineering Geology journal, free available at the following link