Are earthquake activity, volcanic activity, and tectonic plates realated?
Yes. Movement of tectonic plates drive the occurrence for some earthquakes and volcanoes, but not all. Convergent plates are the big culprit. Two plates of differing densities cause one plate to slide under another, melting the rocks of the plate. The density decreases and molten rock moves upward through weaknesses in rock creating volcanoes. Deep earthquakes are associated with this. Those of same density, create mountains like the Himalayas. Not volcanoes, but you can bet lots of earthquakes. Those are still going on because the Himalayas are still growing. Plates that slide past each other instead of up or down, cause earthquakes like the San Andreas. Those are more near surface but can be devestating. There is also volcanism and earthquakes at divergent plate boundaries (rifting).
