Distinct crustal isostasy trends east and west of the Rocky Mountain Front

Schmandt, Brandon; Lin, Fan-Chi; Karlstrom, Karl E.

Distinct crustal isostasy trends east and west of the Rocky Mountain Front

Type

Article

Authors

Schmandt, Brandon

Lin, Fan-Chi

Karlstrom, Karl E.

KAUST Grant Number

OCRF-2014-CRG3-2300 (F.-C.L.)

Online Publication Date

2015-12-14

Print Publication Date

2015-12-16

Date

2015-12-14

Abstract

© 2015. American Geophysical Union. All Rights Reserved. Seismic structure beneath the contiguous U.S. was imaged with multimode receiver function stacking and inversion of Rayleigh wave dispersion and ellipticity measurements. Crust thickness and elevation are weakly correlated across the contiguous U.S., but the correlation is ∼3-4 times greater for separate areas east and west of the Rocky Mountain Front (RMF). Greater lower crustal shear velocities east of the RMF, particularly in low-elevation areas with thick crust, are consistent with deep crustal density as the primary cause of the contrasting crust thickness versus elevation trends. Separate eastern and western trends are best fit by Airy isostasy models that assume lower crust to uppermost mantle density increases of 0.18 g/cm3 and 0.40 g/cm3, respectively. The former value is near the minimum that is plausible for felsic lower crust. Location of the transition at the RMF suggests that Laramide to post-Laramide processes reduced western U.S. lower crustal density.

Citation

Schmandt B, Lin F-C, Karlstrom KE (2015) Distinct crustal isostasy trends east and west of the Rocky Mountain Front. Geophysical Research Letters 42: 10,290–10,298. Available: http://dx.doi.org/10.1002/2015GL066593.

Acknowledgements

Seismic data used in the study are openly available from the IRIS DMC(http:/ds.iris.edu/ds/nodes/dmc/), and the 3D seismic model will be available through the IRIS Earth Model Collaboration (http://ds.iris.edu/ds/products/emc/). Steve Hansenprovided informal feedback. Two anonymous reviewers provided comments thatimproved the manuscript. This research was supported by NSF grant EAR-1315856(B.S.), NSF grant CyberSEES-1442665 (F.-C.L.) and the King Abdullah University ofScience and Technology (KAUST) under Award No. OCRF-2014-CRG3-2300 (F.-C.L.).