TOTAL SLIP ESTIMATES OF THE 7.1M (JULY 2019) SEISMOGENIC AIRPORT LAKE FAULT SYSTEM, RIDGECREST, CALIFORNIA

The 2019 Ridgecrest, California 7.1M and 6.4M earthquakes occurred on a linked fault system of dextral and sinistral faults, respectively. The southern end of new fault scarps occurred on a previously unidentified portion of the Airport Lake fault (ALF). The ALF and associated faults are part of the active zone of deformation of the dextral Walker Lane/Eastern California shear zone, accommodating ~25% of the relative plate boundary motion. This area is located just north of the transversely oriented sinistral Garlock fault. Portions of the southern ALF cut the Spangler Hills, which consists of plutonic rocks containing 1000s of Late Jurassic dikes. The southern ALF also cuts Pliocene and Pleistocene rocks from which other slip markers can be identified. We seek to examine the slip history and evolution of the ALF by identifying slip markers of different ages across the ALF and also for the neighboring fault systems.

The NNW-striking ALF cuts a system of NNE-striking felsic dikes within the plutonic rocks of the Spangler Hills. These dikes vary individually by thickness, which allows matching up of the dikes across the ALF. Slip estimates using multiple dikes yields approximately 1540 meters of right-lateral slip on a 5 km wide zone of 4 principal faults. Farther south, near the terminus with the Garlock fault, Pliocene rocks are interpreted to be right-laterally offset by 1530 meters across a similar system of faults. This implies that all of the ALF slip is post 3.3 Ma. The ALF also offsets Pleistocene rocks in the same area, but no definitive slip markers have yet been identified. The ALF is linked to a WSW-striking sinistral fault system, the Spangler Hills fault zone on which the 6.4M quake occurred. Several dikes along these faults yield approximately 1670 meters of sinistral slip that connects the ALF to another dextral fault system to the west, the Cerro Coso fault (CCF). The CCF has slip markers that show 7360 and 1920 meters of right-lateral offset on two main splays. We interpret the dynamics and evolution of these fault systems in the context of regional dextral shear and the large-magnitude slip sinistral Garlock fault. The interpretation shows that the locus of dextral slip appears to have shifted from the CCF eastward to the ALF and that a new splay of the Garlock fault may be forming and evolving through the Spangler Hills.