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.
Large shallow earthquakes also happen where two plates are pulling apart with the creation of new oceanic crust along mid-ocean ridges and on the transform faults that intersect them. Shallow intraplate earthquakes occur in the relatively stable interior of continents away from plate boundaries.
Shallow, intermediate and deep focus earthquakes occur at_____. The largest earthquakes occur at _____.