What event is most likely to cause a shear break in pipelines?

A shear break in pipelines typically occurs when external forces exert significant pressure on the pipe structure. Earth movements, such as earthquakes, can create intense ground shaking and shifting, which increases the likelihood of shear stress on pipelines. This stress can exceed the material's structural integrity, leading to a break or failure at weak points.

Heavy rainfall may lead to soil erosion and flooding but does not directly impart the shear forces necessary to cause a structural failure in pipes. Excessive water usage can increase pressure within the pipelines but doesn't typically result in shear breaks. Freezing temperatures can cause the material of the pipes to become brittle, but they do not create the specific type of mechanical stress associated with shear breaks that earth movements can. Thus, the presence of intense ground movement during an earthquake is the most significant factor contributing to shear breaks in pipelines.