In recent days there has been a lot of talk about earthquake in Avellino of October 25, characterized by a magnitude of 4.0. and a depth of 14km. Even though it is a Campania location, it is best not to get confused: it is not an earthquake related to Phlegraean bradyseism but it falls within the normal seismicity of the Apennine chain. From a technical point of view, according to the first statements from INGV, it could be a reverse fault. But what does it consist of? And what are its characteristics from a technical and geological point of view?
Faults, in general, are nothing more than fractures of the earth’s crust which cause a movement of the massifs present along the floor breaking (called fault blocks). Depending on the mutual movement between the two blocks it is possible to distinguish various types of fault: in the case of Avellino the roof block (the top one) made one scrolling above that a Bed (the lower one), rising, as shown in the image below.
This type of movement is indicative of a compression and, usually, the angle of these faults is around 30°. The most significant characteristic of these faults is that, being the product of compression, they produce overlaps which at the macroscale and over the course of geological eras are capable of giving life to mountain ranges.
Attention: Does this mean that only reverse faults exist in mountain environments? In reality, no: these are extremely complex environments and nothing prevents a prevalence of relaxing forces on a local scale. In this case the so-called “normal faults“, characterized by an angle usually around the 60° and by a mutual movement of separation between the two blocks.
