Gum disease generally develops because of improper brushing and flossing habits, although underlying medical conditions may have a correlation to greater incidence. The bacteria that are found in the mouth as a result of these poor habits begin to affect the surrounding bone and tissues below the gumline.
Most earthquakes occur at the boundaries where the plates meet. In fact, the locations of earthquakes and the kinds of ruptures they produce help scientists define the plate boundaries. There are three types of plate boundaries: spreading zones, transform faults, and subduction zones.
Convergent Boundaries-deep focus earthquakes common here Earthquakes also occur at divergent boundaries but these earthquakes actually occur at faults caused by the divergent boundary. Source(s):