What is a better guide to plate boundaries than the location of volcanoes?

The location of earthquakes is indeed a more reliable guide to plate boundaries compared to the location of volcanoes. This is because earthquakes occur primarily at the edges of tectonic plates, where different types of interactions—such as subduction, collision, or sliding past each other—take place. These interactions create stress that builds up until it's released as seismic waves, resulting in earthquakes.

In contrast, while volcanoes are often found near plate boundaries—particularly at convergent and divergent boundaries—there can also be volcanic activity related to hotspots that are not associated with plate boundaries. Therefore, earthquakes provide a clearer and more direct representation of the dynamic processes occurring at those boundaries. The distribution of seismic activity can help seismologists construct a more precise map of plate boundaries, highlighting the zones where tectonic plates either collide or separate.