Earthquakes produce three types of seismic waves: primary waves, secondary waves, and surface waves. Each type moves through materials differently. In addition, the waves can reflect, or bounce, off boundaries between different layers.
three key points:
1. they all change the earth by shifting plates in different ways.
2. these waves lead to our plates form today, which are always changing.
3. even the smallest earthquakes make the slightest changes to our ground. and many happen in just a day! we just never feel it.
