Most tectonic activity occurs near the surface where rocks are cool and brittle. As you go deeper, the increasing heat makes rocks more “ductile” (pliable), meaning they tend to flow rather than break. Shallow quakes occur along all types of plate boundaries, including transform faults and mid-ocean ridges. Because the focus is close to the surface, the seismic waves haven’t traveled far enough to lose energy through “attenuation,” which is why shallow quakes like the 2010 Haiti event cause such massive devastation compared to deeper quakes of the same magnitude.