Explain the difference between relative plate velocity and absolute plate velocity. (B)

Relative plate velocity is a measure of how fast one tectonic plate is moving in relation to another. It is often expressed in centimeters per year (cm/yr) or millimeters per year (mm/yr). Relative plate velocity can be calculated based on the observed movement of Earth's lithosphere or by using geophysical models. Gaining an understanding of relative plate velocities helps geoscientists predict future plate interactions and the resulting geological events, such as earthquakes and volcanic eruptions.

Absolute plate velocity is a measure of how fast a tectonic plate is moving with respect to a fixed reference frame, such as Earth's mantle or a hotspot. Similar to relative plate velocity, it is typically expressed in centimeters per year (cm/yr) or millimeters per year (mm/yr). Absolute plate velocity provides a more comprehensive view of a plate's motion, taking into account the fact that not only are the plates themselves moving, but the reference frame (such as Earth's mantle) may also be experiencing motion.

The primary difference between relative plate velocity and absolute plate velocity lies in the reference frame used to measure a plate's motion. Relative plate velocity compares the movement of one plate to another, while absolute plate velocity measures a plate's motion in relation to a fixed reference frame (e.g. the mantle or a hotspot). Another important distinction is that relative plate velocity focuses on the interactions between two specific plates, while absolute plate velocity considers a plate's motion globally. This means that relative velocity may be useful in studying localized geological events or predicting the future development of specific plate boundaries, while absolute velocity can provide insights into overall plate dynamics and how they have evolved through Earth's history.

To better understand the difference between relative and absolute plate velocities, consider the following example: The Pacific Plate and the North American Plate are interacting along California's San Andreas Fault. The relative plate velocity along this boundary can be measured by observing the movement of the Pacific Plate with respect to the North American Plate, whereas the absolute plate velocity would require measuring the motion of each plate in relation to a fixed point in Earth's mantle or a hotspot. By comparing these measurements, geoscientists can gain a more comprehensive understanding of the tectonic forces at play along the boundary and better predict future events such as earthquakes.