Growth of surface-breaching normal faults as a three-dimensional fracturing process

Abstract

Structures along the Hopena normal fault of the Koae fault system (KFS) on Kilauea volcano, Hawaii, provide a record of fault propagation in three dimensions. This fault displays (1) a breached monocline along the scarp; (2) a belt of discontinuous echelon fractures along the scarp and past its end; (3) a belt of discontinuous fractures on the footwall; (4) buckles at the base of the scarp; and (5) a belt of discontinuous fractures on the hangingwall that converges towards the end of the fault trace. Solid mechanics analyses show that this ensemble can be accounted for by the tipline of a normal fault propagating up towards the surface (accompanied by antithetic fracturing), then intersecting it and propagating laterally. Normal fault propagation down from the surface cannot account for the observed structures. Lateral slip occurs along some fractures as a result of local stress changes associated with fault propagation. Discontinuous fractures at the surface form early above a blind normal fault and continue to develop as a normal fault propagates laterally. Linkage of the fractures to the fault produces a fault with an irregular trace. The discontinuous, irregular character of normal fault traces over a broad range of scale is an inevitable consequence of three-dimensional fault growth.