How much the volcano is vibrating, measured by INGV seismometers near the craters. One value every ten minutes, for four stations, compared with the previous days.
Tremor now · ECPN
941nm/sat 11:40 · 0.5–2.5 Hz
Compared with normal
within the usual range
usually between 730 and 2,741 nm/s (27 days, up to two days ago)
In the last hour
steady
−6 % compared with the three hours before
High frequencies · 4–10 Hz
2,352nm/swithin the usual range
Tremor · 0.5–2.5 Hz · Cratere del Pianonm/s
every 10 minuteshourly averagewhere it usually sitsINGV VONA (the colour is the aviation code)
High frequencies · 4–10 Hz · Cratere del Pianonm/s
Move your finger or mouse over the chart to read the values.
Tremor is not an earthquake. Earthquakes are single events; tremor is a continuous vibration of the ground which, on Etna, comes from gas and magma moving through the conduits. It usually rises before and during lava fountains and drops when they end.
nm/s means nanometres per second: the speed at which the ground moves. A thousand nm/s is a thousandth of a millimetre per second: nobody feels it, seismometers record it.
The chart rises in powers of ten: each numbered line is worth ten times the one below. That way calm days and strong moments fit on the same chart.
Each station has its own numbers. The closer it is to the craters, the more it picks up. That is why we do not use the same thresholds for all: we compare each station with its own last 30 days.
High frequencies (4–10 Hz) follow the faster vibrations closer to the surface, such as explosions and degassing; strong wind at the summit can raise them too.
Tremor alone does not tell whether an eruption will happen. INGV reads it together with other measurements; for the state of the volcano, its bulletins and VONAs are what count.
Source: INGV national seismic network, stations ECPN, ECNE, EPDN and EMFS (open data, CC BY 4.0). Data processed in real time by Trinaka every ten minutes; Italian time.