All earthquakes
3.3
weak
EARTHQUAKE DETAILS

7 km East of Villa di Chiavenna

110 months ago · 23 Aug, 09:30

A weak earthquake, felt by some of the population. At only a few km deep the shaking is felt more sharply at the surface.

Stronger than 99% of Italian events in the past yearNo. 3 of the year in LombardiaThe strongest of the past 12 months within 50 km

Where

7 km East of Villa di ChiavennaEarthquakes in the province of SondrioEarthquakes in Lombardia

How far away could it be felt?

An estimate of how far people may have felt this quake.

  • up to ~18 km · felt only by some, at rest
    ≈ 32,000 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

4 events
Magnitude:lightweakmoderatestrong

The energy released

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

1.3tof TNT equivalent
5.6 lightning bolts
M3
×2.8 the energy of a magnitude 3 earthquake
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 ≈ 24 s

Animation sped up ~5× compared to reality.

  • Como
    70 km from the epicentre
    first tremor in ~12 s
    main shaking in ~20 s
  • Bergamo
    70 km from the epicentre
    first tremor in ~12 s
    main shaking in ~20 s
  • Varese
    81 km from the epicentre
    first tremor in ~14 s
    main shaking in ~23 s
  • Monza
    85 km from the epicentre
    first tremor in ~14 s
    main shaking in ~24 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

1 km
shallow

At only a few km deep the shaking is felt more sharply at the surface.

shallower than 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
0
last 7 days
0
last 30 days
1 before2 after
this quake
Strongest of the sequence1.3

How often does it happen here?

about every ~3.9 years

Within 50 km of this epicentre, a magnitude ≥ 3 earthquake has occurred on average this often: 3 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.

18514.7
Valtellina earthquake
5 February 1851 · 23 km from here
V-VIStrong: felt by everyone, many get scared; objects fall, first light damage to buildings.
19914.7
Grigioni, Vaz earthquake
20 November 1991 · 46 km from here
VIStrong: felt by everyone, many get scared; objects fall, first light damage to buildings.
15124.6
Valchiavenna earthquake
8 February 1512 · 15 km from here
VIStrong: felt by everyone, many get scared; objects fall, first light damage to buildings.
19174.6
Alta Engadina earthquake
9 December 1917 · 21 km from here
VIIVery strong: hard to stand; chimneys and roof tiles fall, serious damage to weaker buildings.

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

The closest seismic structure

Western S-Alps internal thrust

The epicentre lies about 63 km from Western S-Alps internal thrust, one of the seismic structures mapped by INGV geologists.

estimated maximum magnitude 6.9between 5 and 12 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

1.3
5 km North-East of Lanzada
28 km East · 11 km
110 months ago
24 Aug, 09:53
0.8
6 km East of Lanzada
30 km East · 12 km
110 months ago
11 Aug, 20:41
1.0
4 km West of Lanzada
21 km East · 10 km
109 months ago
5 Sept, 12:27

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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