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Título

UNDERSTANDING THE INFLUENCE OF PREEXISTING PLANAR HETEROGENEITIES ON SUBSIDIARY STRUCTURES NUCLEATION IN STRIKE-SLIP FAULT ZONE: ANALOG MODELING AND PIV ANALYSIS

Texto do resumo

Preexisting structures in the basement can be reused, facilitating the reactivation, nucleation, and propagation of new faults and fractures. The process of reactivating preexisting structures, or their influence on the nucleation of new ones, depends on the orientation of their geometric arrangement relative to the new stress field. This study investigates how preexisting planar structures, with different orientations, influence the initiation and development of subsidiary structures within a strike-slip fault zone, thereby assessing potential reactivations. Physical sandbox experiments were conducted to simulate dextral strike-slip tectonics, and their surface strain patterns were analyzed using the Particle Image Velocimetry (PIV) technique. Preexisting structures were simulated by introducing a planar discontinuity into the model through “pre-cuts” before deformation. The experiments were based on the orientation of preexisting structures relative to north (conventionally defined as perpendicular to the direction of extension): 015°, 045°, 075°, 090°, 285°, 315°, 345° Az. A “reference experiment” was performed without preexisting structures. A velocity discontinuity (VD) was placed at the bottom of the apparatus to nucleate an E-W trending strike-slip tectonics. During the strike-slip deformation, preexisting structures oriented at 285°Az, 345°Az, 075°Az, and 090°Az were reactivated on the orientation of R-, R’-, P-, and Y-type subsidiary fractures relative to the current tectonic, respectively. All inherited fractures in these orientations were reactivated. However, the preexisting fractures oriented at 315°Az, 015°Az, and 045°Az remained inactive. The inherited structure-oriented E-W exhibited the fastest development of the continuous main fault, induced a smaller damage zone, and exhibited the lowest vertical displacement. The maximum strain concentration sites detected by the PIV data revealed the nucleation of structures before they were visible to the naked eye. Models with preexisting structures oriented at 015°Az delayed fracture nucleation despite visible strain concentration. Models without preexisting structures or with those oriented at 345°Az had delayed development of the continuous main fault (shear zone core or Riedel Y-fault). Our results emphasize the importance of the geometric relationship between the preexisting structure and the new applied stress field. They demonstrate that this relationship dictates whether a structure will be reactivated; even when potentially unfavorable for reactivation, preexisting structures can impact the formation of new structures. The implications of these findings are significant, as fractures and faults within strike-slip fault zones can act as conduits for fluid migration in prospective economic areas, making understanding deformation behavior in the context of preexisting structures essential.

Palavras Chave

preexisting structures; strike-slip fault; physical modeling; PIV