4 km North-West of Castiglione d'Orcia
A very light earthquake, probably not felt by people. At only a few km deep the shaking is felt more sharply at the surface.
Where
4 km North-West of Castiglione d'OrciaEarthquakes in the province of SienaEarthquakes in ToscanaHow far away could it be felt?
A quake this small is usually not felt by people: only seismographs record it.
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
4 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.
- Siena40 km from the epicentrefirst tremor in ~7 smain shaking in ~12 s
- Arezzo57 km from the epicentrefirst tremor in ~10 smain shaking in ~17 s
- Perugia63 km from the epicentrefirst tremor in ~11 smain shaking in ~18 s
- Grosseto67 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 (~9 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: 127 months ago the same area had a stronger quake (M2.2). 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 ≥ 2 earthquake has occurred on average this often: 263 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 65 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).