1. some areas where earthquakes and volcanic activity often occur together are along oceanic ridges where lithospheric plates move apart. if we know the age of the crust and the distance from the ridge center, we can calculate how fast the two plates are moving away from each other. look at the figures of oceanic ridges (spreading centers) a. calculate the half-spreading rate across the mid-atlantic ridge and east pacific rise. this is the rate at which one of the plates is growing.

b. determine the full spreading rate for these same ridges. this is the rate at which the ocean basins are opening