Final answer:
Earthquake risk in the U.S. varies mainly due to differences in tectonic plate boundaries, variations in underground rock composition, and human activities. Areas where tectonic plates collide or slide past each other, like the San Andreas Fault, are particularly prone to earthquakes. Human-induced seismicity also adds to the risk in some regions.
Step-by-step explanation:
The risk of earthquakes varies across the U.S. primarily due to Differences in Tectonic Plate Boundaries. The Earth's crust consists of tectonic plates that move and interact at their edges. Where plates slide past each other or collide, tremendous stress builds up, which, when released, results in earthquakes. The U.S. has several fault zones, like the San Andreas Fault in California, which is part of the boundary between the Pacific and North American plates.
Furthermore, the variation in underground rock composition affects seismic waves and the damage they can cause. Different materials can either amplify or dampen seismic energy, influencing the intensity of quakes felt on the surface.
Influence of Human Activities on Seismicity also contributes to the risk of quakes in certain areas, like those associated with oil and gas extraction or reservoir-induced seismicity.
The provided theories and observations on plate tectonics, underground rock compositions, and human activities help in understanding and managing the risks associated with earthquakes.
Learn more about Tectonic Plates