Starting August 24, the teams of geologists of EMERGENCY, one of the seismic emergency operational groups for the geological surveys of the National Institute of Geophysics and Volcanology (INGV), have taken action to carry out the first surveys on the effects of earthquakes on the territory, focusing on both primary cosismic effects (i.e. directly related to earthquake rupture such as surface faulting and fracturing) than on those secondary (or attributable to the shaking caused by seismic waves such as landslides, landslides, collapse of boulders, liquefaction, etc.). Objective of these teams, investigate the epicentral area for a total length of about 40 km between Castelluccio di Norcia, to the north, and the Ortolano locality located south of the artificial lake of Campotosto. At the moment, geological information on about 2400 observation points has been catalogued. In general, numerous fractures along the mountain slopes and cultivated fields were reported throughout the investigated area (these deformation elements are often clearly visible on the road surface), together with landslides, landslides and small-medium sized boulders.
Surface fracture with evidence of vertical displacement observed along an active fault.
An earthquake is the effect of the sudden relative sliding of the rock masses that make up the earth's crust along the so-called rupture zones faults. The big earthquakes, with a magnitude generally greater than 6, produce effects not only on the built, but also permanent deformations on the earth's surface in an area as wide as some hundreds of km2. These deformations are the direct consequence of the relative displacement of the portions of the earth's crust along the fault plane (direct or primary effects), but also due to the passage of the seismic wave (indirect or secondary effects).
- direct effects they are those that take place at the intersection of the fault plane, which has moved, with the earth's surface. In fact, here, the displacement occurred in depth is highlighted with the formation of fractures aligned with the fault plane and which often form a real step (fault escarpment). These elements reflect the movement on the fault in depth both in geometry, magnitude and direction of displacement, and they are generally associated with geological faults marked in the dedicated thematic maps as active faults.
Other direct effects of the earthquake are the lowering/raising of portions of the earth's surface (yellow arrows in the figure above) that can be observed with both terrestrial and satellite study methods (geodesy and remote sensing). When these deformations are large, they can produce superficial effects visible even to the naked eye, such as for example swamping, flooding, or emergence of important portions of the territory.
Among the effects indirect, therefore not necessarily related to the movement on the fault plane but only as a response to the shaking produced by the earthquake, fracturing without regular geometric organization, liquefaction and landslides are the most common.
La liquefaction it takes place in the presence of loose deposits, mainly sandy and saturated in water, therefore we will preferably observe it in alluvial and coastal plains. The passage of the seismic wave creates overpressures in the saturated levels which leads to their liquefaction (loss of cohesion of the soil up to assuming a behavior typical of fluids) and to the consequent migration of the liquefied material towards the surface. The brakes they are triggered by ground accelerations on steep and generally unstable slopes even in normal conditions.
With the exception of the liquefaction phenomenon of which no reports have yet been received, all the other effects seem to have been produced in the epicentral area of the Amatrice earthquake of 24 August 2016.
More information can be found in First preliminary report of the EMERGEO Operational Group on cosismic effects, Available at Italian and English.