OBLIQUE RIFTING, CROSS-FAULT DOMAINS, AND ACTIVE DETACHMENT FAULTS

Geodetic results have shown deformation across the zone that extends NNW-SSE between the Sierra Nevada (SN) and the western Basin & Range (B&R) province (e.g., Bennett et al., 1999; Gan et al., 2000; Miller et al., 2001; Lifton et al., 2013; Thatcher et al., 2016; Klein et al, 2019). Earthquakes, geothermal fields, and young volcanics delineate this active belt called the Walker Lane (e.g., Faulds and Henry, 2008). We describe and interpret commonalities between fault geometries observed in three cross-fault domains that all lie within the inboard oblique rift zone (IORZ) marked by the Gulf of California Shear Zone (Bennett & Oskin, 2014), Salton Trough, Coachella Valley, Eastern California Shear Zone, and Walker Lane. Cross-faults that broke in the 2019 Ridgecrest earthquake sequence accommodate transtension across the southern Walker Lane. Similar sets of faults broke in the Yuha Desert, at the NW end of the 2010 El Mayor – Cucapah rupture, and along the Elmore Ranch Fault Zone during the 1987 Superstition Hills sequence. A series of mid-crustal low angle normal faults accommodate extension and allow upper crustal blocks to rotate above. We infer that, at these three locations, the simultaneously active main right-lateral NW-SE oriented faults and secondary left-lateral NE-SW oriented ‘cross-faults’ at Superstition Hills, Yuha Desert, and Airport Lake are kinematically stable because of a low friction mid-crustal delamination surface. Surface-rupturing earthquake sequences in 1987, 2010 and 2019 have shown the mechanics of cross-fault interaction that may be expected in fault sets possessing similar geometrical configurations. The Big Bear aftershock of the Landers sequence in 1992 provides another example, as do many smaller sequences (e.g., 1984 Round Valley, 1986 Chalfant Valley, 1995 Ridgecrest, 1979, multiple sequences in the Brawley Seismic Zone, 2016 Nine Mile Ranch) through which cross-faulting is well-expressed by seismicity. As the 1987 & 2019 sequences have shown, behavior such as delayed triggering, associated with cross-fault interaction, may tend to be localized within the cross-faulting regimes we identify within this IORZ. Several of these may be active metamorphic core complexes, and these are co-located with geothermal fields at Cerro Prieto, Salton Sea & Coso (e.g., Monastero et al., 2005).