Lets now consider a problem formulated by Means (1976) and discussed vividly by Davis and Reynolds (1996). The problem, simply stated, is what would be the stress on a horizontal surface 1500 m across at the base of a 3.375x109m3 cube of granite in the upper crust?
As illustrated in Figure 4 the cube of granite extends from the Earth’s surface to a depth of 1500 m and has a uniform density of 2700 kg/m3. The force generated by the weight of the cube of granite is:
which upon multiplying out reduces to 8.93025 x 1013 kg-m/sec2 (or N). Recalling from our previous discussions that stress is force acting over some surface area, we divide this value by the area of the base of the cube of granite:
which reduces to 39,690,000 N/m2 or 39.69 MPa.