How many times have we happened to hear about hypocenter and epicenter Shortly after an earthquake? Italy is a region with a high seismic risk and often happens that the news of a new earthquake will become part of the insights of the national news. So, you will surely have come across the terms hypocenter and epicenter And you will probably also ask yourself what they differ. THE’hypocenter It is the point of origin of the earthquake while theepicenter It is its corresponding point on the surface on the vertical and both are used as parameters to locate a seismic event. Let’s see what I am and what their difference is.
Hypocentro and epicenter in comparison
To fully understand the difference between hypocenter and epicenter, it is necessary to keep in mind the causes of an earthquake. In the world, most of the SISMI have tectonic origin, That is, it is linked to the business of fault, which can be both new, and already existing and reactivated. A fault is one fracture or discontitity which occurs in the earth’s crust, separating a volume of rock into two blocks. These slide in opposite directions along the separation surface, called fault plan. The breakdown and relative movement of rock volumes in the subsoil are accompanied by Energy releasewhich spreads in all directions in the form of seismic waves.
The depth point in which the rocks takes place from which the seismic waves propagate is said hypocenter. This is found on the fault plane. The depth of the hypocentro varies considerably from A few hundred meters up to 700 km – in the case of the deepest earthquake ever recorded – mainly in operation of the Geodynamic and tectonic context.
THE’epicenter instead represents the vertical projection of the hypocentro on the earth’s surfaceand is indicated with geographical coordinates. In most earthquakes, the epicenter coincides with the point or area where the earthquake has the greatest intensity.
How they determine
Following the activation of a fault, two types of seismic waves spread from subsoil to the surface: Longitudinal wavesalso called compressive waves or waves “P“(Primary) and the transversal wavesalso called cutting waves or waves “Sort“(Secondary). Between the two, the” P “waves are the fastest, while the” S “waves travel to about 60% of the speed of the compressive waves and do not propagate in the fluids. The different speed of propagation of the waves “P” and “S” and the gap in Times of arrival at seismomtric stations which record the earthquake on the surface are the parameters used to identify the hypocenter and epicenter of an earthquake.
To geolocate the epicenter, the method of the triangulation. There difference in arrival times between primary and secondary waves it is used to calculate the distance of at least three seismographic stations from the epicenter (epicentral distance). The greater the interval between the arrival times, the greater the distance of the seismograph from the epicenter. Subsequently, for each station, a circumference is traced whose radius corresponds to the epicentral distance. The intersection point Among the three circumferences he identifies the epicenter. The difference in the arrival times of the “P” and “S” waves can also be used to mathematically estimate the hypocenter of the earthquake, but in this case considering only the seismograph closest to the epicenter.
The National Institute of Geophysics and Volcanology (Ingv), which manages the seismic monitoring network on the national territory, takes between 2 and 5 minutes to provide a first estimate of the attributes of an earthquake with a magnitude greater than 3.0.
