Assessing potential multi-segment large-magnitude paleo-earthquakes on the Compton blind thrust fault beneath metropolitan Los Angeles

Matthew P. Salinas, Lorraine A. Leon, Chris Anthonissen, James F. Dolan, John H. Shaw, & Thomas L. Pratt

Submitted August 30, 2026, SCEC Contribution #15471, 2026 SCEC Annual Meeting Poster #TBD

The Compton thrust is a 40-km-long blind thrust fault extending beneath the western part of the Los Angeles metropolitan region. An earlier paleoseismological study by Leon et al. (2009) utilized seismic reflection profiles and a transect of continuously cored boreholes to investigate near-surface fault-related folding along the back limb axial surface of the northern segment of the Compton thrust. These studies revealed that the northern segment of the Compton thrust generated six stratigraphically discrete folding events during the last 14,000 years, with thrust displacements between 1.3 and 4.2 m, consistent with Mw ≥ 7.0 earthquakes. As the Compton thrust is segmented between a northern and southern section, comparison between the two is needed to characterize segmentation behavior of previous events. In this study, we utilize a second data set consisting of high-resolution seismic reflection profiles and a transect of continuously cored boreholes collected across the locus of active folding above the southern segment in the city of Lakewood to investigate the nature and timing of paleo-ruptures on the Compton thrust. Preliminary analysis of these data reveals an upward-narrowing growth triangle defined by progressive folding of fluvial strata. High-resolution dating of multiple event horizons defined by these paleo-fold scarps will produce and improved paleo-earthquake chronology as well as an incremental fault slip-rate record. In addition to facilitating comparison of paleo-earthquake ages between segments of the Compton Thrust, this refined paleoseismic record will allow us to explore the behavior of Compton Thrust relative to other urban faults in the greater metropolitan Los Angeles region, including the Puente Hills Thrust, Newport-Inglewood, Palos Verdes and other nearby faults. The new Compton Thrust data from the Lakewood site will be critical for understanding the system-level behavior of the urban fault network as well as for developing more accurate seismic hazard assessments in one of the most populous regions in the country.

Key Words
Paleoseismology, Earthquake Geology

Citation
Salinas, M. P., Leon, L. A., Anthonissen, C., Dolan, J. F., Shaw, J. H., & Pratt, T. L. (2026, 08). Assessing potential multi-segment large-magnitude paleo-earthquakes on the Compton blind thrust fault beneath metropolitan Los Angeles. Poster Presentation at 2026 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology