Determination of paleoearthquake age and slip per event data, and Late Pleistocene-Holocene slip rates on a blind-thrust fault: Application of a new methodology to the Puente Hills thrust fault, Los Angeles County, California

The Puente Hills thrust fault (PHT) is an active, blind-thrust fault that generated the 1987 M 6.0 Whittier-Narrows earthquake. In this study, we developed and tested a multi-disciplinary, collaborative methodology for assessing the seismic hazards of blind-thrust faults, focusing on the forelimb growth triangles of the Santa Fe Springs and West Coyote Hills anticlines associated with slip on the PHT. High-resolution seismic reflection images revealed dipping reflectors in a narrowing upwards zone that continues to with 10 m of the surface. Borehole transects across this zone along the Santa Fe Springs segment revealed a discrete zone of south-dipping strata measuring ∼300 m wide at 25 meters depth and ∼100--160 m wide at 2 meters depth. Stratigraphic and structural relationships revealed evidence for four magnitude >7.0 events in the past 11,000 years. Slip rates generated along both segments of the PHT range from 0.95 to 2.1 mm/yr.