Model MCQs

Explanation :

Earthquakes occur in the crust or upper mantle of the Earth, which ranges from the earth's surface to about 700 kilometers deep.

• Below that depth, rocks tend to bend and flow rather than break, since the area is too hot and ductile.
• In seismology, the depth at which an earthquake occurs is called depth of focus or focal depth.
• Earthquakes are labeled "shallow" if they occur at less than 50 kilometers of depth and they are labeled "deep" if they occur at 300-700 kilometers of depth.
• Earthquakes with depths from 50 kilometers to 300 kilometers are labeled “intermediate”.
• In general, shallow earthquakes tend to be more damaging than deeper ones, since seismic waves from deep earthquakes travel farther to the surface, losing energy along the way.
• The strength of an earthquake shaking at the surface that occurs at 400 kilometers deep is noticeably less than if an earthquake occurred at 10 kilometers depth.
• Moreover, shallow-focus earthquakes often produce much more aftershocks than deep-focus earthquakes.
• The deeper-focus earthquakes commonly occur in patterns called Benioff zones that dip into the Earth, indicating the presence of a subducting slab.