16. What type of boundary occurs where two plates move together, causing one plate to descend into the mantle beneath the other plate? a. convergent boundary c. transform fault boundary b. divergent boundary d. transitional boundary 17. According to the theory of plate tectonics, a. the asthenosphere is divided into plates b. the asthenosphere is strong and rigid C. the asthenosphere moves over the lithosphere d. the lithosphere is divided into plates 18. Where does the first motion of an earthquake occur? a. epicenter C. focus b. fault d. locus​