At a _._._ plate boundary, tectonic plates are moving past each other in opposite directions.

At a **transform** plate boundary, tectonic plates are moving past each other in opposite directions. **Explanation:** Plate boundaries are categorized based on the movement of the tectonic plates relative to each other. There are three primary types of plate boundaries: 1. **Divergent Boundaries:** Here, plates move apart from each other. This movement typically occurs at mid-ocean ridges where new crust is formed as magma rises from beneath the Earth's surface. 2. **Convergent Boundaries:** At these boundaries, plates move toward each other. This can result in one plate being forced below another in a process called subduction, leading to the formation of mountain ranges, volcanic activity, or deep ocean trenches. 3. **Transform Boundaries:** This is the type that fits your description. At transform boundaries, plates slide horizontally past each other. The motion is typically in opposite directions along the fault line. A well-known example of a transform boundary is the San Andreas Fault in California. **Key Characteristics of Transform Boundaries:** - **Horizontal Movement:** Unlike divergent and convergent boundaries, the primary movement at transform boundaries is horizontal. - **Earthquakes:** The friction and interaction between the sliding plates can cause earthquakes. - **No Significant Crust Creation or Destruction:** Unlike divergent and convergent boundaries, transform boundaries do not typically involve the creation or subduction of crust. Understanding the nature of transform boundaries is crucial for comprehending seismic activity in regions where these boundaries are present.