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EARTHQUAKE DETAILS

9 km South-West of Acate

69 months ago · 22 Dec, 21:37

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

Stronger than 88% of Italian events in the past year

Where

9 km South-West of AcateEarthquakes in the province of RagusaEarthquakes in Sicilia

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

5 events
Magnitude:lightweakmoderatestrong

The energy released

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

15kgof TNT equivalent
Less than the energy of a lightning bolt
M3
A magnitude 3 earthquake releases ×32 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 ≈ 14 s

Animation sped up ~3× compared to reality.

  • Vittoria
    11 km from the epicentre
    first tremor in ~5 s
    main shaking in ~8 s
  • Gela
    18 km from the epicentre
    first tremor in ~5 s
    main shaking in ~9 s
  • Ragusa
    27 km from the epicentre
    first tremor in ~6 s
    main shaking in ~11 s
  • Modica
    42 km from the epicentre
    first tremor in ~8 s
    main shaking in ~14 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

26 km
medium depth
3 times the height of Mount Everest

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

deeper than the area average (~21 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 (M4.4, 69 months ago) in the same area. Aftershocks are normal after an earthquake and tend to fade over time.

4.4
The mainshock
8 km West of Vittoria
69 months ago · 22 Dec, 21:27
Activity in the area right now (30 km radius)
0
last 24 hours
0
last 7 days
1
last 30 days
1 before3 after
this quake
Strongest of the sequence4.4

How often does it happen here?

about every ~36 days

Within 50 km of this epicentre, a magnitude ≥ 2 earthquake has occurred on average this often: 118 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.

18185.6
Monti Iblei earthquake
1 March 1818 · 43 km from here
VII-VIIIRuinous: partial collapses in ordinary buildings, widespread heavy damage.
16245.6
Monti Iblei settentrionali earthquake
3 October 1624 · 47 km from here
IXDestructive: many buildings partly or fully collapse.
19095.3
Caltagirone earthquake
2 January 1909 · 33 km from here
VII-VIIIRuinous: partial collapses in ordinary buildings, widespread heavy damage.
19495.1
Sicilia sud-orientale earthquake
8 October 1949 · 28 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

Gela-Catania

The epicentre lies about 18 km from Gela-Catania, one of the seismic structures mapped by INGV geologists.

estimated maximum magnitude 7.1between 3 and 10 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

4.4
8 km West of Vittoria
4 km South-East · 30 km
69 months ago
22 Dec, 21:27
1.6
9 km South-West of Acate
1 km East · 25 km
69 months ago
23 Dec, 00:37
1.4
10 km South-West of Acate
2 km West · 26 km
69 months ago
23 Dec, 01:39
1.6
69 months ago
25 Dec, 13:45

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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