Why might the 1990 earthquake and volcanic eruption in luzon be related? a) both earthquakes and volcanic eruptions are caused by plate tectonics and can occur in patterns. b)earthquakes occur in san francisco but not in chicago. c) tectonic plates can form deep ocean trenches, such as the mariana trench in the pacific ocean. d) on april 2, mount pinatubo sent an explosion of steam, water, ash, and rock into the air.