M4.0 earthquake · 9 km North-West of Forlì (FC)
A moderate earthquake, felt by people in the area. At this depth the shaking is felt, but rarely causes damage.
Where
9 km North-West of ForlìEarthquakes in the province of Forlì-CesenaEarthquakes in Emilia-RomagnaHow far away could it be felt?
An estimate of how far people may have felt this quake.
- up to ~10 km · felt by many people, especially on upper floors≈ 174,000 people live in this area
- up to ~42 km · felt only by some, at rest≈ 929,000 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
8 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 ~2× compared to reality.
- Faenza8 km from the epicentrefirst tremor in ~3 smain shaking in ~6 s
- Forlì9 km from the epicentrefirst tremor in ~3 smain shaking in ~6 s
- Ravenna19 km from the epicentrefirst tremor in ~4 smain shaking in ~7 s
- Imola25 km from the epicentrefirst tremor in ~5 smain shaking in ~9 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 this depth the shaking is felt, but rarely causes damage.
in line with the area average (~14 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 an aftershock: it follows a stronger quake (M4.3, 9 months ago) in the same area. Aftershocks are normal after an earthquake and tend to fade over time.
How often does it happen here?
Within 50 km of this epicentre, a magnitude ≥ 4 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 sits above this source area: the deep structure where this area's earthquakes can originate.
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).