Formation Mechanisms and Petroleum Significance of Complex Normal Fault Networks in the Linbei and Panhe Areas, Bohai Bay Basin, China

Orthorhombic normal fault networks in sedimentary basins and their formation mechanisms are of significant geological importance. Orthorhombic normal fault networks and planar H-shaped normal fault networks (HNF) developed in distinct locations along the Linshang dextral transtensional fault, with the HNF on the eastern hanging wall and the orthorhombic normal fault networks on the western footwall. Using 2D and 3D seismic data, we investigated the geometry, evolution, and formation mechanisms of these fault networks within the regional tectonic context. The HNF consists of systematically arranged E–W-trending normal faults and N–S-trending cross normal faults. The orthorhombic normal fault networks comprise four sets of normal faults. Expansion indices and balanced cross-section analyses indicate that both these networks formed contemporaneously during the E2s3 stage. Mechanical analysis suggests that differences in the local stress field led to the development of these networks in different segments of the Linshang Fault. The HNF formed sequentially within a single tectonic phase. In contrast, the orthorhombic normal fault networks developed within a 3D strain field driven by the combined effects of dextral transtension along the Linshang Fault and footwall tilting. Hydrocarbon exploration results confirm that these normal fault networks exert significant control on hydrocarbon migration pathways and accumulation patterns.