M3.1 earthquake · 4 km North of Sora (FR)
A weak earthquake, felt by some of the population. At only a few km deep the shaking is felt more sharply at the surface.
Where
4 km North of SoraEarthquakes in the province of FrosinoneEarthquakes in LazioHow far away could it be felt?
An estimate of how far people may have felt this quake.
- up to ~13 km · felt only by some, at rest≈ 91,000 people live in this area
The coloured rings on the map below show these distances.
Statistical estimate from the Italian intensity attenuation model (INGV): actual perception depends on geology, buildings and depth. Very shallow events can be felt locally even below the threshold.
Earthquake map
40 eventsThe energy released
How much energy this quake unleashed, translated into everyday comparisons.
Each extra magnitude unit releases about 32 times more energy: an M5 is not "a bit stronger" than an M4 — it is a different league.
Energy estimated with the standard Gutenberg–Richter relation; an average lightning bolt ≈ 1 billion joules. Indicative values.
The race of the seismic waves
Two waves set off from the hypocentre: the faster P wave arrives first with a sharp jolt; the S wave carries the actual shaking.
Animation sped up ~4× compared to reality.
- L'Aquila62 km from the epicentrefirst tremor in ~10 smain shaking in ~18 s
- Velletri70 km from the epicentrefirst tremor in ~12 smain shaking in ~20 s
- Latina70 km from the epicentrefirst tremor in ~12 smain shaking in ~20 s
- Tivoli72 km from the epicentrefirst tremor in ~12 smain shaking in ~21 s
Theoretical times with average crustal speeds: real values vary with geology. The gap between P and S waves is what earthquake early-warning systems rely on.
How deep it was born
At only a few km deep the shaking is felt more sharply at the surface.
in line with the area average (~12 km)
For the same magnitude, a shallow earthquake is felt much more than a deep one: the energy starts closer to the surface.
What kind of quake is this?
In hindsight it was a foreshock: 7 years ago the same area had a stronger quake (M4.1). This can only be said after the fact — it was not predictable beforehand.
How often does it happen here?
Within 50 km of this epicentre, a magnitude ≥ 3 earthquake has occurred on average this often: 26 events in the last 12 years of the INGV catalogue.
An average computed on the recent past: it tells how used this area is to shaking, not when the next quake will come — earthquakes cannot be predicted.
The great earthquakes in this area's history
Almost a thousand years of catalogues: the strongest documented events within ~50 km.
Source: Parametric Catalogue of Italian Earthquakes CPTI15 (INGV, CC BY 4.0).
The closest seismic structure
The epicentre lies about 11 km from Salto Lake-Ovindoli-Barrea, one of the seismic structures mapped by INGV geologists.
Faults are mapped to build better and understand the territory: knowing them says nothing about when an earthquake will occur, which remains unpredictable. Source: DISS 3.3 (INGV, CC BY 4.0).
Other quakes in the area
Data: INGV — National Institute of Geophysics and Volcanology (CC-BY 4.0)
Estimates computed by Meteare on INGV data (Gutenberg–Richter relation; Italian macroseismic intensity attenuation model).