Volcanic Tremor

Earthquakes happen almost everywhere – the sudden breaking of rocks to release tension built up in the crust and the shaking as the energy waves reach the surface.   In some places, such as close to the boundaries between lithospheric plates, these events can happen frequently.  In other areas, like mid-plate, they are uncommon events. 

The movement of magma in the crust can also build up tension, as it squeezes its way through the rocks, causing earthquakes to occur in volcanic areas.   Often these are discrete earthquake events, each being able to be measured for its location, depth, and magnitude, and these events can provide scientists with great information to understand the movement of magma and assist with them in predicting volcanic eruptions.

An earthquake event on Kilauea.

However, when there is a large injection of magma, these earthquake events become so frequent that they run into each other – the ground is continually shaking (normally at a relatively low energy level) and this is called volcanic tremor.

Unlike earthquakes, volcanic tremor can last for hours, days, or even longer.  The tremor may precede an eruption and continue while the eruption is taking place.

Below is the seisogram trace from Kilauea, Hawaii in January 29, 1997, showing the onset of volcanic tremor.