What evidence led scientists to believe that waves travel at a greater velocity inside Earth?
A) Studies of earthquake signals via sensors located deep inside drill holes prove it.
B) Refraction of energy waves is most efficient at shallower depths.
C) Refraction of energy waves is most efficient along short paths.
D) Average velocity is faster when the seismograph is farther from the focus of the earthquake.
Question 2
What was the reason for installing a worldwide network of seismometers in the 1950s and 1960s?
A) to save human lives by predicting volcanic eruptions and earthquakes
B) to study plate tectonic theory
C) to monitor underground nuclear bomb testing
D) to study mine blasts
