If both earthquakes are of the same magnitude, why can an earthquake that occurs east of the Rockies produce damage over a larger area than the damage produced by an earthquake in California?
(a) The bedrock in the eastern and central United States is less rigid than that in the western United States, which allows seismic waves to travel greater distances with less attenuation.
(b) The bedrock in the eastern and central United States is more rigid than that in the western United States, which allows seismic waves to travel greater distances with more attenuation.
(c) The bedrock in the eastern and central United States is unconsolidated in many areas, whereas the bedrock in the western United States is very rigid. The unconsolidated bedrock allows seismic waves to travel greater distances with more attenuation.
(d) The bedrock in the eastern and central United States is more rigid than that in the western United States, which allows seismic waves to travel greater distances with less attenuation.

The rigidity of rock layers plays an important role in the propagation of the seismic waves that we feel during an earthquake. In the case of the bedrock in the central and eastern parts of the United States, the older and more compacted rock layers provide a more efficient medium through which the seismic waves travel more quickly and in a comparatively uninterrupted fashion.