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EARTHQUAKE DETAILS

M2.5 earthquake outside Italy

11 years ago · 14 Sept 2015, 23:36

A light earthquake, rarely felt by people. At this depth the shaking is felt, but rarely causes damage.

Where

Nearest Italian town: Valdieri (CN)Earthquakes in the province of CuneoEarthquakes in Piemonte

Epicentre abroad

The epicentre lies outside Italy's borders. The quake appears here because the INGV seismic network also records events close to Italy, which can be felt on Italian territory.

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

9 events
Magnitude:lightweakmoderatestrong

The energy released

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

85kgof TNT equivalent
Less than the energy of a lightning bolt
M3
A magnitude 3 earthquake releases ×5.6 its energy
M2this quakeM4

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 ≈ 29 s

Animation sped up ~5× compared to reality.

  • Cuneo
    40 km from the epicentre
    first tremor in ~7 s
    main shaking in ~12 s
  • Sanremo
    56 km from the epicentre
    first tremor in ~10 s
    main shaking in ~16 s
  • Moncalieri
    100 km from the epicentre
    first tremor in ~17 s
    main shaking in ~29 s
  • Savona
    101 km from the epicentre
    first tremor in ~17 s
    main shaking in ~29 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

11 km
medium depth
1.2 times the height of Mount Everest

At this depth the shaking is felt, but rarely causes damage.

in line with the area average (~10 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?

Mainshock

It is the strongest quake of its sequence: so far it has been followed by 2 aftershocks within 30 km. Aftershocks tend to fade in number and strength over time.

Activity in the area right now (30 km radius)
0
last 24 hours
5
last 7 days
8
last 30 days
6 before2 after
this quake
Strongest of the sequence1.9

How often does it happen here?

about every ~3 months

Within 50 km of this epicentre, a magnitude ≥ 2.5 earthquake has occurred on average this often: 45 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.

15645.8
Lantosque earthquake
20 July 1564 · 14 km from here
VIII-IXDestructive: many buildings partly or fully collapse.
16445.7
Alpes Niçoises earthquake
15 February 1644 · 19 km from here
VIIIRuinous: partial collapses in ordinary buildings, widespread heavy damage.
16185.6
Alpes Niçoises earthquake
18 January 1618 · 22 km from here
VIIIRuinous: partial collapses in ordinary buildings, widespread heavy damage.
19194.9
Alpi Marittime earthquake
28 November 1919 · 44 km from here
V-VIStrong: felt by everyone, many get scared; objects fall, first light damage to buildings.

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

The closest seismic structure

Brianconnais

The epicentre lies about 41 km from Brianconnais, one of the seismic structures mapped by INGV geologists.

estimated maximum magnitude 7.2between 5 and 20 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

1.7
4 km West of Moiola
20 km North-East · 15 km
11 years ago
11 Sept 2015, 10:24
1.9
5 km South-West of Moiola
19 km North-East · 14 km
11 years ago
9 Sept 2015, 10:56
1.2
2 km North-East of Demonte
21 km North · 10 km
11 years ago
22 Sept 2015, 02:47
0.9
2 km West of Rittana
27 km North-East · 10 km
11 years ago
31 Aug 2015, 05:29
0.8
8 km South-West of Valdieri
6 km North-East · 11 km
11 years ago
30 Aug 2015, 03:23
1.0
11 years ago
5 Oct 2015, 20:39
0.7
1 km West of Roaschia
21 km North-East · 10 km
11 years ago
20 Aug 2015, 09:44
1.4
11 km South-West of Vinadio
19 km West · 14 km
11 years ago
19 Aug 2015, 10:29

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).