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Seismic imaging of the metamorphism of young sediment into new crystalline crust in the actively rifting Imperial Valley, California

Han, Liang and Hole, John A. and Stock, Joann M. and Fuis, Gary S. and Williams, Colin F. and Delph, Jonathan R. and Davenport, Kathy K. and Livers, Amanda J. (2016) Seismic imaging of the metamorphism of young sediment into new crystalline crust in the actively rifting Imperial Valley, California. Geochemistry, Geophysics, Geosystems, 17 (11). pp. 4566-4584. ISSN 1525-2027. http://resolver.caltech.edu/CaltechAUTHORS:20170223-074555793

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Abstract

Plate-boundary rifting between transform faults is opening the Imperial Valley of southern California and the rift is rapidly filling with sediment from the Colorado River. Three 65–90 km long seismic refraction profiles across and along the valley, acquired as part of the 2011 Salton Seismic Imaging Project, were analyzed to constrain upper crustal structure and the transition from sediment to underlying crystalline rock. Both first arrival travel-time tomography and frequency-domain full-waveform inversion were applied to provide P-wave velocity models down to ∼7 km depth. The valley margins are fault-bounded, beyond which thinner sediment has been deposited on preexisting crystalline rocks. Within the central basin, seismic velocity increases continuously from ∼1.8 km/s sediment at the surface to >6 km/s crystalline rock with no sharp discontinuity. Borehole data show young sediment is progressively metamorphosed into crystalline rock. The seismic velocity gradient with depth decreases approximately at the 4 km/s contour, which coincides with changes in the porosity and density gradient in borehole core samples. This change occurs at ∼3 km depth in most of the valley, but at only ∼1.5 km depth in the Salton Sea geothermal field. We interpret progressive metamorphism caused by high heat flow to be creating new crystalline crust throughout the valley at a rate comparable to the ≥2 km/Myr sedimentation rate. The newly formed crystalline crust extends to at least 7–8 km depth, and it is shallower and faster where heat flow is higher. Most of the active seismicity occurs within this new crust.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1002/2016GC006610DOIArticle
http://onlinelibrary.wiley.com/doi/10.1002/2016GC006610/abstractPublisherArticle
ORCID:
AuthorORCID
Stock, Joann M.0000-0003-4816-7865
Additional Information:© 2016 American Geophysical Union. Received 29 AUG 2016; Accepted 28 OCT 2016; Accepted article online 3 NOV 2016; Published online 18 NOV 2016. We thank the Editor Thorsten Becker and three anonymous reviewers for their helpful and constructive reviews. This research was supported by NSF MARGINS and EarthScope grants 0742263 to J.A.H. and 0742253 to J.M.S., by the U. S. Geological Survey's Multihazards Research Program, and by the Southern California Earthquake Center (SCEC) (Contribution No. 6244). We thank the >90 field volunteers and USGS personnel who made data acquisition possible. Numerous landowners acknowledged in Rose et al. [2013] allowed access for shots and stations. Seismographs and technical support were provided by the IRIS-PASSCAL instrument facility; special thanks go to Mouse Reusch and Patrick Bastien from PASSCAL for their field and data efforts. Software support was provided by Landmark Software and Services, a Halliburton Company. The data have been archived at the IRIS DMC (http://ds.iris.edu/pic-ph5/metadata/SSIP/form.php).
Group:Seismological Laboratory
Funders:
Funding AgencyGrant Number
NSFOCE-0742263
NSFOCE-0742253
USGSUNSPECIFIED
Southern California Earthquake Center (SCEC)UNSPECIFIED
Subject Keywords:active rifting; metamorphism; passive margin; Salton Trough; Imperial Valley; seismic refraction tomography
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Southern California Earthquake Center (SCEC)6244
Record Number:CaltechAUTHORS:20170223-074555793
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20170223-074555793
Official Citation:Han, L., J. A. Hole, J. M. Stock, G. S. Fuis, C. F. Williams, J. R. Delph, K. K. Davenport, and A. J. Livers (2016), Seismic imaging of the metamorphism of young sediment into new crystalline crust in the actively rifting Imperial Valley, California, Geochem. Geophys. Geosyst., 17, 4566–4584, doi:10.1002/2016GC006610
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:74487
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:02 Mar 2017 03:32
Last Modified:02 May 2017 18:25

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