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- Title
Compositional Variation in the Crust of Peninsular Ranges and Surrounding Regions, Southern California, Revealed by Full‐Wave Seismic and Gravity Joint Inversion.
- Authors
Bao, Xueyang; Guo, Lianghui; Shen, Yang
- Abstract
Detailed three‐dimensional models of crustal compositional variations are essential for better understanding crustal evolution and dynamics. High‐resolution wave speed and density models of the crust provide one of the most important constraints on crustal compositional variations, particularly at depths beyond direct rock sampling. Here we present a three‐dimensional density and wave speed model of Southern California obtained by jointly inverting gravity anomalies and seismic component‐differential phase delays with full‐wave sensitivity kernels, which provide a link between wave speed and density. Thus, unlike previous joint seismic and gravity inversions, the new model does not depend on an empirical relationship between wave speed and density. The resulting density and compressional‐to‐shear wave‐speed ratio (Vp/Vs) reveal detailed features of compositional variations in the upper and middle crust in the study area, such as the three‐dimensional geometry of the boundary between the western and eastern portions of the Peninsular Ranges batholith, the gabbro‐ and metavolcanics‐rich locations within the Western Peninsular Ranges batholith, the variation of sedimentary basin thickness beneath the Coachella Valley, and a likely intermediate‐to‐mafic batholith beneath the Coachella Valley and the Eastern Peninsular Ranges. The jointly inverted density and Vp/Vs values also suggest a lithological control on seismic activities off the major fault zones. Plain Language Summary: Precise 3D models of the compositional variation in the crust are important for understanding geology and resource distribution. At depths where direct rock sampling is unattainable, the speeds of seismic energy traveling within the Earth and density derived from geophysical observations provide key evidence to uncover crustal composition. We present a new method of using gravity and seismic waveform data together to construct a 3D density and wave speed model of Southern California. The resulting model reveals the detailed structure of density and the ratio between compressional and shear wave speeds from the surface to about 20 km depth in this area, showing significant geological features including the 3D geometry of a compositional boundary within the Peninsular Ranges (a group of north‐south trending mountain ranges in Southern California) that reflects an old crustal suture, locations of rock types of differing contents of magnesium and iron, variation of sedimentary basin thickness, and a separate batholith beneath the Coachella Valley sedimentary basin and the eastern Peninsular Ranges. The model also suggests a relationship between crustal composition and earthquake distribution outside of the major fault zones in Southern California. Key Points: We develope a full‐wave tomographic inversion with gravity data to image 3D crustal density and velocity structures in Southern CaliforniaThe joint inversion model remains self‐consistent though the inversion doesn't depend on empirical relation between wave speeds and densityThe density and Vp/Vs models outline the 3D compositional variations within the upper and middle crust of Southern California
- Subjects
SOUTHERN California; CRUST of the earth; SEISMIC waves; GRAVITY; GEODYNAMICS; PETROLOGY
- Publication
Journal of Geophysical Research. Solid Earth, 2021, Vol 126, Issue 12, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2021JB022723