All earthquakes
1.6
very light
EARTHQUAKE DETAILS

M1.6 offshore earthquake

9 years ago · 21 Jul 2017, 14:23

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 74% of Italian events in the past year

Where

Nearest Italian town: Laigueglia (SV)Earthquakes in the province of SavonaEarthquakes in Liguria

Epicentre at sea

The epicentre is at sea: for the same magnitude, the shaking is felt less on land, because the energy fades along the way before reaching the coast.

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

10 events
Magnitude:lightweakmoderatestrong

The energy released

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

3.8kgof TNT equivalent
Less than the energy of a lightning bolt
M3
A magnitude 3 earthquake releases ×126 its energy
M1this quakeM3

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 ≈ 27 s

Animation sped up ~5× compared to reality.

  • Savona
    47 km from the epicentre
    first tremor in ~8 s
    main shaking in ~14 s
  • Sanremo
    56 km from the epicentre
    first tremor in ~10 s
    main shaking in ~16 s
  • Genova
    66 km from the epicentre
    first tremor in ~11 s
    main shaking in ~19 s
  • Cuneo
    94 km from the epicentre
    first tremor in ~16 s
    main shaking in ~27 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

10 km
shallow
1.1 times the height of Mount Everest

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 (M1.9, 9 years ago) in the same area. Aftershocks are normal after an earthquake and tend to fade over time.

1.9
The mainshock
Costa Ligure centro-occidentale (Savona)
9 years ago · 14 Jul 2017, 00:17
Activity in the area right now (30 km radius)
0
last 24 hours
0
last 7 days
0
last 30 days
3 before6 after
this quake
Strongest of the sequence1.9

How often does it happen here?

about every ~5 months

Within 50 km of this epicentre, a magnitude ≥ 2 earthquake has occurred on average this often: 31 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 · 39 km from here
XCompletely destructive: most buildings are destroyed.
18185.3
Liguria occidentale earthquake
23 February 1818 · 35 km from here
VIIIRuinous: partial collapses in ordinary buildings, widespread heavy damage.
19635.0
Mar Ligure earthquake
27 July 1963 · 46 km from here
VIStrong: felt by everyone, many get scared; objects fall, first light damage to buildings.
19684.9
Liguria occidentale earthquake
18 April 1968 · 39 km from here

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

The closest seismic structure

Imperia Promontory

The epicentre sits above this source area: the deep structure where this area's earthquakes can originate.

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

1.9
Costa Ligure centro-occidentale (Savona)
12 km East · 11 km
9 years ago
14 Jul 2017, 00:17
1.5
Costa Ligure centro-occidentale (Savona)
23 km East · 23 km
9 years ago
30 Jul 2017, 14:39
0.5
16 km South-East of Noli
24 km North · 11 km
9 years ago
5 Aug 2017, 13:43
1.0
9 years ago
2 Jul 2017, 18:01
0.9
Costa Ligure centro-occidentale (Savona)
15 km South-West · 16 km
9 years ago
10 Aug 2017, 22:09
1.2
20 km South-East of Noli
21 km North-East · 9 km
9 years ago
12 Aug 2017, 07:12
1.5
20 km South-East of Noli
20 km North-East · 8 km
9 years ago
12 Aug 2017, 07:22
1.1
16 km South-East of Noli
24 km North · 10 km
9 years ago
26 Jun 2017, 04:29
1.4
18 km South-East of Cervo
20 km West · 14 km
9 years ago
17 Aug 2017, 03:16

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).