Each year on Planet Earth there are about 500,000
earthquakes and about 1,500 volcanoes have activity. While
even Richter 5.0 earthquakes at shallow depths and at the
wrong location can be both deadly and costly (damage to  
Christchurch in New Zealand may well exceed $20 billion)  
usually one wishes to be concerned about 7.5 Richter or
greater events, especially if they occur underwater. Similarly,
VEI=6 volcanic events such as the Mt. Pinatubo eruption in
1991 in the Philippines can not only devastate local areas but
endanger whole national economies. Despite timely
evacuations that saved many lives, the immediate direct cost to
the Philippines was close to $15 billion, and weather and crops
over half the globe were impacted.
Today, the intensity of swarms of hundreds of small
earthquakes can be used to determine that lava is moving, and
that an explosion can be expected. A second test is to analyze
emissions for the isotope ratios of the element neodymium.