https://opentextbc.ca/geology/chapter/4-5-monitoring-volcanoes-and-predicting-eruptions/

According to the text:

"....well-placed seismometers can provide us with an early warning that something is changing beneath one of the volcanoes, and that we need to take a closer look."

"If there is seismic evidence that a volcano is coming to life, more seismometers should be placed in locations within a few tens of kilometres of the source of the activity (Figure 4.26). This will allow geologists to determine the exact location and depth of the seismic activity so that they can see where the magma is moving."