KINEMATIC CONNECTION BETWEEN THE GARLOCK AND PINTO MOUNTAIN FAULTS, MOJAVE BLOCK, SOUTHERN CALIFORNIA: A NEW PROPOSAL

The Garlock fault (Gf) and Pinto Mountain fault (PMf) are major tectonic elements along the Pacific-North American transform plate boundary. I propose that the San Andreas Fault (SAF) and Eastern California Shear Zone (ECSZ) kinematically link the Gf and the PMf, a proposal that builds on the work of Dixon & Xie (2018) and Hatem & Dolan (2018). The SAF drags the west ends of the Gf and PMf 9.9 km and 10.0 km respectively to the northwest while being deflected westward. As a result, the Gf and PMf lengthen to 0.7 and 2.0 km respectively. Conjugate slip from the San Andreas Fault over the past 3 Ma contributed 15–18 km slip to the western Gf at a 5–6 mm/yr slip rate and 9–12 km slip at a 3–4 mm/yr rate to the central Gf (Hatem & Dolan, 2018). Although the PMf surely started out as a conjugate shear plane to the SAF, conjugate slip contribution to the Holocene (and Pleistocene?) PMf would be almost nothing because it is presently at an orientation unfavorable for conjugate slip to occur. I suggest that the ECSZ transfers strain to the Gf and PMf by oroclinal bending, block rotation, and coseismic slip. Oroclinal bending of the eastern Gf (Hatem & Dolan, 2018) and PMf (this study) occurred in response to right-lateral shear across the ECSZ resulting in the observed CW rotations in the Northeastern Mojave and Eastern Transverse Ranges domains. Oroclinal bending contributed ~2.4 km of left slip to the Gf over a 3 Ma period assuming a slip rate of 0.8 mm/yr (Hatem & Dolan, 2018). Slip contribution from oroclinal bending of the eastern PMf is unknown because the eastern ~25 km is inactive and a slip rate has not been established. Using a slip rate of 1.3–2.3 mm/yr over 14 Ka years (Cadena et al., 2004), oroclinal bending contributed 18.2–32.2 m of slip to the central PMf. Coseismic slip contributions to the Gf and PMf appears to be variable. The July 2019 Ridgecrest Earthquake Sequence triggered 9 m of left slip along a ~30-km zone of slip closest to the epicenter, whereas slip along the entire eastern Gf was “negligible” (Ross et al., 2019). The 1992 Landers Earthquake Sequence yielded 2 cm of coseismic slip along the PMf based on right-stepping cracks (Hart et al., 1993). Shear strain along the Gf is absorbed by folding, local thrust faulting, block rotations, and tectonic escape, while along the PMf strain is absorbed by local folding and block rotation.