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Sedimentary injectites hosted within basement rocks, where preserved on land, offer a means to investigate the geometry, extent, dimensions and spacing of fractures that form an interconnected network within faulted/fractured crystalline host rock. Hydrocarbon occurrences within fractured basement are of high interest following the success of basement-targeted exploration in the North Sea and UK continental shelf. In some cases, these settings lack direct access to the fractured basement that constitute the crystalline-rock reservoir, due to the presence of a thick sedimentary cover. For this reason, we investigated two regional-scale crystalline-rock-hosted systems of sedimentary injectites and sediment-filled fractures that occupy basement fracture arrays within granitoids. Localities are in the Serre massif of Calabria, Italy and the Front Range of Colorado (USA). The injected sediment within fractures acts as a natural ‘proppant’ that maintained open pathways for fluid migration or accumulation. Study of the arrays of sediment-filled fractures and faults advances our understanding of unconventional fluid migration pathways, controls upon the porosity and permeability, and the potential of crystalline basement rock to act as a hydrocarbon reservoir.

Upper‐plate faulting in the Olympic Peninsula of Washington State results from relative motion of crustal blocks within the Cascadia forearc and earthquake cycle processes along the Cascadia subduction zone. We reconstruct fault slip rates since ∼14 ka on the Sadie Creek fault (SCF), north of the Olympic Mountains, using airborne lidar and field mapping of surficial deposits and landforms and optically stimulated luminescence and radiocarbon dating. The SCF is a ≥14 km‐long northwest‐striking, subvertical, dextral strike‐slip fault with a subordinate dip‐slip component. Laterally, offset debris flow channels cut into Late‐Pleistocene and younger surfaces show dextral slip of 4.0–24.5 m and dip slip of 0.7–6.5 m. Re‐evaluation of fault slip on the adjacent Lake Creek Boundary Creek fault (LCBCF) shows similar dextral (4.5–29.7 m) and dip slip (0.8–4.6 m). A deglacial age of 14 ka paired with the largest—and presumably oldest—slip measurements produce a minimum dextral slip rate of 1.3–2.3 mm/yr and dip‐slip rate of 0.05–0.5 mm/yr. Similarities in geometry, kinematics, slip rate, and earthquake timing between the SCF and LCBCF suggest these faults represent one continuous geologic structure, the North Olympic fault zone. Geodetically constrained boundary element method models considering the effects of coseismic subduction zone stresses on upper plate structures produce comparable kinematics to those measured on the SCF and LCBCF, suggesting that the North Olympic fault zone acts as the main strain‐accommodating structure in the northern Olympic Peninsula and may be modulated by stress transferred from subduction zone earthquakes. The Sadie Creek fault is characterized by a minimum post‐14 ka slip rate of 1.3–2.3 mm/yrSimilarities in slip between the Sadie Creek fault and Lake Creek Boundary Creek fault suggest these faults represent one continuous structure, the North Olympic fault zoneComparison of measured and modeled slip rates suggest crustal faults may be modulated by stress transferred from subduction zone earthquakes The Sadie Creek fault is characterized by a minimum post‐14 ka slip rate of 1.3–2.3 mm/yr Similarities in slip between the Sadie Creek fault and Lake Creek Boundary Creek fault suggest these faults represent one continuous structure, the North Olympic fault zone Comparison of measured and modeled slip rates suggest crustal faults may be modulated by stress transferred from subduction zone earthquakes