Tectonic evolution of the Salton Sea inferred from seismic reflection data

Abstract

The Salton Sea is an evolving pull-apart basin located between the San Andreas and Imperial faults in Southern California. Seismic and geological data reveal a rapidly subsiding southern sub-basin that is bounded by a hinge zone to the north, and northwest-dipping normal faults to the south. Oblique extension across strike-slip faults causes subsidence and leads to the formation of pull-apart basins such as the Salton Sea in southern California. The formation of these basins has generally been studied using laboratory experiments or numerical models1,2,3,4. Here we combine seismic reflection data and geological observations from the Salton Sea to understand the evolution of this nascent pull-apart basin. Our data reveal the presence of a northeast-trending hinge zone that separates the sea into northern and southern sub-basins. Differential subsidence (>10 mm yr−1) in the southern sub-basin suggests the existence of northwest-dipping basin-bounding faults near the southern shoreline, which may control the spatial distribution of young volcanism. Rotated and truncated strata north of the hinge zone suggest that the onset of extension associated with this pull-apart basin began after ∼0.5 million years ago. We suggest that slip is partitioned spatially and temporally into vertical and horizontal domains in the Salton Sea. In contrast to previous models based on historical seismicity patterns5, the rapid subsidence and fault architecture that we document in the southern part of the sea are consistent with experimental models for pull-apart basins1.