1. Boundaries between different layers of the Earth:
* The Moho discontinuity: This is the boundary between the Earth's crust and the mantle. It is marked by a significant change in density and mineral composition.
* The Core-Mantle Boundary (CMB): This is the boundary between the Earth's mantle and the outer core. It is a sharp transition from solid rock to liquid iron and nickel.
* The Inner Core-Outer Core Boundary: This is the boundary between the liquid outer core and the solid inner core.
2. Other Geological Structures:
* Subduction Zones: Where tectonic plates collide, one plate may slide beneath the other, creating a dipping zone of high density.
* Fault Zones: Fractures in the Earth's crust where rocks have moved past each other.
* Large Igneous Intrusions: Bodies of solidified magma that can act as barriers to seismic waves.
* Significant changes in rock density: Even gradual changes in rock density can cause seismic waves to refract (bend) or reflect.
3. The Earth's Surface:
* The Earth's surface: While not strictly "beneath" the surface, seismic waves can reflect off the surface itself, especially during earthquakes.
How Reflections Help Scientists:
The reflections of seismic waves are essential for understanding the Earth's interior. By analyzing the timing and characteristics of reflected waves, seismologists can:
* Determine the depth and composition of Earth's layers: Reflections help map out the major boundaries within the Earth.
* Identify and characterize geological structures: Reflections can reveal faults, subduction zones, and other features.
* Monitor seismic activity: Studying reflected waves can help track the movement of magma and predict potential volcanic eruptions.
So, earthquake waves don't just travel through the Earth; they bounce off its internal structures, providing valuable information about our planet's composition and dynamics.
