Fine-scale partitioning of contemporary strain in the southern Walker Lane: Implications for accommodating divergent strike-slip motion

Treating the crust as a micropolar continuum and inverse modeling a high-quality catalog of earthquake focal mechanisms reveals that >km-scale heterogeneous strain is partitioned at ∼km-scales into pairs of plane strains with sub-perpendicular principal axes. These earthquakes occurred in a shallow crustal volume centered on the western Indian Wells Valley of eastern California, the site of divergent, right-lateral strike-slip motion along the boundary between the Sierran microplate and the southern Basin and Range province. The seismic events defining the plane strains occur in a diffuse seismic source zone and cannot be additionally subdivided on the basis of the type of strain they accommodate. The results indicate that seismic moment release for background earthquakes is partitioned into events associated with either fault-zone-perpendicular extension by normal faults or horizontal shearing by conjugate strike-slip faults. The spatial scales over which this partitioning occurs suggest that outcrop-scale brittle faults may in some cases record nearly perpendicular plane strains related to a single continuous deformation.