What term describes a state of stress where one principal stress is normal to the earth's surface in continental crust basins?

What term describes a state of stress where one principal stress is normal to the earth's surface in continental crust basins?

• A. Andersonian State of Stress
• B. Brittle-ductile transition
• C. Lithostatic pressure
• D. Shear-dominated regime

Answer: (A)

Andersonian State of Stress describes how the three principal stresses are oriented relative to gravity, which tells you what kind of faulting to expect. When one principal stress points straight down to the Earth’s surface—the vertical direction—the other two are horizontal, and the specific faulting you get depends on which is the largest. In continental basins that are stretching apart, the vertical stress is the smallest (sigma3), so the rock tends to split and drop along normal faults. That combination—vertical stress being one principal stress and driving extension—is what the Andersonian framework uses to classify this stress state. The other terms don’t describe this orientation. Brittle-ductile transition is about temperature and pressure where rocks switch deformation styles, not about the direction of stresses. Lithostatic pressure is isotropic, pushing equally in all directions. A shear-dominated regime emphasizes horizontal shear, not the vertical normal component described here.

Andersonian State of Stress describes how the three principal stresses are oriented relative to gravity, which tells you what kind of faulting to expect. When one principal stress points straight down to the Earth’s surface—the vertical direction—the other two are horizontal, and the specific faulting you get depends on which is the largest. In continental basins that are stretching apart, the vertical stress is the smallest (sigma3), so the rock tends to split and drop along normal faults. That combination—vertical stress being one principal stress and driving extension—is what the Andersonian framework uses to classify this stress state.

The other terms don’t describe this orientation. Brittle-ductile transition is about temperature and pressure where rocks switch deformation styles, not about the direction of stresses. Lithostatic pressure is isotropic, pushing equally in all directions. A shear-dominated regime emphasizes horizontal shear, not the vertical normal component described here.