Become a physicist and maybe one day you can tell me.
The geologic force applied to rocks is called compression. Compression<span> is the stress that squeezes </span>rocks<span> together. As a result of the c</span>ompression rocks fold or fracture depending on their compressive strength<span> or </span>compression strength<span> - the capacity of a material or structure to withstand loads tending to reduce size.
</span>When the compression is horizontal the crust will be s<span>hortened and thickened.</span><span> When the compression is vertical maximum a section of rock will fail in </span>normal faults<span>, horizontally extending and vertically thinning a given layer of rock.</span>
Figure A shows cross section of a land form or rock. In Figure B, compression stress is applied on it. When compression stresses are applied on a rock, it squeezes the rock cause fold or fracture. The fault formed by compression stress is called thrust fault. If the compression stresses/ force continue to act on a rock it will converge and form thrust fault. In Figure C, tension stresses is applied on the rock. When a tension stress applied on a rock it deforms/ lengthen. There are three type of deformations occur due to tension stresses. One is elastic deformation, in which, rock retains it original shape when force/stresses are removed. Second is plastic deformation, in which rock lengthen and change occur permanently. Third type of deformation is result into fracture or breaking of rock. In Figure C, shear stresses are applied on rock. Shear stresses are applied with equal magnitude but in opposite direction. It cause breaking of rock.
