All earthquakes
1.0
very light
EARTHQUAKE DETAILS

3 km West of Pigna

16 months ago · 21 Apr, 13:40

A very light earthquake, probably not felt by people. At only a few km deep the shaking is felt more sharply at the surface.

Stronger than 30% of Italian events in the past year

Where

3 km West of PignaEarthquakes in the province of ImperiaEarthquakes in Liguria

How 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

12 events
Magnitude:lightweakmoderatestrong

The energy released

How much energy this quake unleashed, translated into everyday comparisons.

0.5kgof TNT equivalent
Less than the energy of a lightning bolt
M3
A magnitude 3 earthquake releases ×1,000 its energy
M0this quakeM2

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.

P waves — the first sharp jolt (~6 km/s)S waves — the strongest shaking (~3.5 km/s)
t ≈ 32 s

Animation sped up ~6× compared to reality.

  • Sanremo
    17 km from the epicentre
    first tremor in ~3 s
    main shaking in ~5 s
  • Cuneo
    52 km from the epicentre
    first tremor in ~9 s
    main shaking in ~15 s
  • Savona
    79 km from the epicentre
    first tremor in ~13 s
    main shaking in ~23 s
  • Genova
    111 km from the epicentre
    first tremor in ~19 s
    main shaking in ~32 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

7 km
shallow

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?

Aftershock

It is an aftershock: it follows a stronger quake (M2.7, 16 months ago) in the same area. Aftershocks are normal after an earthquake and tend to fade over time.

2.7
The mainshock
17 km West of Olivetta San Michele
16 months ago · 21 Apr, 09:37
Activity in the area right now (30 km radius)
0
last 24 hours
1
last 7 days
6
last 30 days
9 before2 after
this quake
Strongest of the sequence2.7

How often does it happen here?

about every ~2 months

Within 50 km of this epicentre, a magnitude ≥ 2 earthquake has occurred on average this often: 69 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.

18876.3
Liguria occidentale earthquake
23 February 1887 · 30 km from here
XCompletely destructive: most buildings are destroyed.
15645.8
Lantosque earthquake
20 July 1564 · 29 km from here
VIII-IXDestructive: many buildings partly or fully collapse.
16445.7
Alpes Niçoises earthquake
15 February 1644 · 32 km from here
VIIIRuinous: partial collapses in ordinary buildings, widespread heavy damage.
16185.6
Alpes Niçoises earthquake
18 January 1618 · 25 km from here
VIIIRuinous: partial collapses in ordinary buildings, widespread heavy damage.

Source: Parametric Catalogue of Italian Earthquakes CPTI15 (INGV, CC BY 4.0).

The closest seismic structure

Imperia Promontory

The epicentre lies about 27 km from Imperia Promontory, one of the seismic structures mapped by INGV geologists.

estimated maximum magnitude 7.4between 3 and 15 km deep

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

2.7
16 months ago
21 Apr, 09:37
1.5
1 km North of Limone Piemonte
29 km North · 10 km
16 months ago
19 Apr, 16:23
1.0
16 months ago
18 Apr, 11:14
0.9
10 km North-West of Triora
13 km North · 5 km
16 months ago
27 Apr, 16:45
0.9
5 km North-West of Pigna
1 km North-West · 9 km
17 months ago
15 Apr, 01:09
1.0
3 km North-West of Pigna
1 km East · 11 km
17 months ago
12 Apr, 08:40
0.7
17 months ago
12 Apr, 02:41
0.9
4 km North-West of Pigna
1 km North-West · 11 km
17 months ago
11 Apr, 22:13
1.1
17 months ago
4 Apr, 22:11
1.2
4 km South of Ventimiglia
18 km South · 10 km
16 months ago
8 May, 17:44

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).

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