M3.4 earthquake · 3 km West of Cetona (SI)
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
3 km West of CetonaEarthquakes in the province of SienaEarthquakes in ToscanaHow far away could it be felt?
An estimate of how far people may have felt this quake.
- up to ~1 km · felt by many people, especially on upper floors
- up to ~21 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
26 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 ~3× compared to reality.
- Perugia43 km from the epicentrefirst tremor in ~7 smain shaking in ~12 s
- Arezzo56 km from the epicentrefirst tremor in ~9 smain shaking in ~16 s
- Siena60 km from the epicentrefirst tremor in ~10 smain shaking in ~17 s
- Viterbo65 km from the epicentrefirst tremor in ~11 smain shaking in ~19 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 (~8 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?
It is the strongest quake of its sequence: so far it has been followed by 19 aftershocks within 30 km. Aftershocks tend to fade in number and strength over time.
How often does it happen here?
Within 50 km of this epicentre, a magnitude ≥ 3 earthquake has occurred on average this often: 8 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 48 km from Mugello-Citta' di Castello-Leonessa, 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).