High-Frequency Receiver Function Profiles Reveal Sedimentary Basin Structure Beneath the Northern Los Angeles Area

Ritu Ghose, Patricia Persaud, Yida Li, Valeria Villa, & Robert W. Clayton

Submitted August 15, 2021, SCEC Contribution #11464, 2021 SCEC Annual Meeting Poster #221

We determine the structure of the San Gabriel, Chino and San Bernardino basins using receiver functions computed along 10 seismic lines of the BASIN (Basin Amplification Seismic Investigation) project. The dataset is comprised of ~790 densely-spaced nodes that recorded for up to 35 days. For each line, receiver functions at different frequencies in the 1- 4 Hz range were computed for 3-5 events with magnitudes >5.9 and epicentral distances of 30°-90°. We converted the sediment-basement Ps travel times to depth using estimates of VP=2.6 km/s and VS=1.1 km/s. The deepest part of the triangular-shaped San Gabriel (SG) basin is located in the flat-lying urbanized area north of the Puente Hills and ~2 km from the Whittier Heights fault. Basin depth ranges from ~700 m in the westernmost part of the SG basin near the Raymond fault to ~3 km in its deepest part. Our results show that faults exhibit a strong control on the shape of San Gabriel basin from the Raymond fault in the northwest, to the Walnut Creek fault in the southeast and the Indian Hill fault in the east. The Chino basin is deepest (~3 km) along the eastern side of the Fontana fault. The Cucamonga and Etiwanda Avenue faults and an extension of the Fontana fault were interpreted in the receiver function profiles. The San Bernardino (SB) basin, sandwiched between the San Andreas and San Jacinto fault zones has basin depths ranging from ~400 m to ~2.5 km. The shallowest part of this basin is to the north near the San Andreas fault. The SB basin deepens southward to ~2.5 km near the Loma Linda fault and then shallows again near the San Jacinto fault zone with a depth of ~1.2 km. Overall, our results show more complexity and non-uniformity in basin structure than previously documented, which would affect seismic wave propagation and basin amplification effects in the region. We find that the central parts of the basins are not the deepest and notable changes in basin depth occur near some faults. Along with the sediment-basement interface, we also identify the Moho and an intracrustal interface throughout the study area. Future work will incorporate a shear wave velocity model developed as part of the BASIN project to improve the basin depth estimates.

Key Words
Basin Depth, Receiver Function, San Bernardino Basin, Chino Basin, San Gabriel Basin, Nodal Seismometer

Ghose, R., Persaud, P., Li, Y., Villa, V., & Clayton, R. W. (2021, 08). High-Frequency Receiver Function Profiles Reveal Sedimentary Basin Structure Beneath the Northern Los Angeles Area. Poster Presentation at 2021 SCEC Annual Meeting.

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