Question

how do scientists use seismic waves to understand earths interior?
a by studying the frequency of seismic waves caused by human activities
b by measuring the intensity of seismic waves during volcanoes
c by analyzing the speed and direction of seismic waves through refraction
d by observing the amplitude of seismic waves in different regions

Explanation:

Seismic waves change speed and direction (refract) as they pass through different materials in Earth's interior. Analyzing these changes helps scientists understand the structure and composition of Earth's interior. Human - caused seismic waves (A) are not the main way. Measuring intensity during volcanoes (B) doesn't directly reveal Earth's interior structure. Observing amplitude in different regions (D) is not the key method for understanding the interior compared to wave speed and direction analysis.

Answer:

C. by analyzing the speed and direction of seismic waves through refraction