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Analysis of teleseismic P waves with a 5200-station array in Long Beach, California: Evidence for an abrupt boundary to Inner Borderland rifting

Schmandt, Brandon and Clayton, Robert W. (2013) Analysis of teleseismic P waves with a 5200-station array in Long Beach, California: Evidence for an abrupt boundary to Inner Borderland rifting. Journal of Geophysical Research. Solid Earth, 118 (10). pp. 5320-5338. ISSN 2169-9313. http://resolver.caltech.edu/CaltechAUTHORS:20140206-114352976

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Abstract

We analyze teleseismic P waves from four Mw ≥ 6.5 earthquakes recorded by a petroleum industry survey in Long Beach, California. The survey used a 2-D array with up to 5200 seismometers, 120 m mean spacing, and 7 – 10 km aperture. At frequencies near 1 Hz, P wave travel times and amplitudes exhibit coherent lateral variations over scales as short as ~400 m, including locally delayed travel times and increased amplitudes at the crest of the Long Beach anticline. Deeper heterogeneity is indicated by P wave phase velocities that deviate from reference model predictions for events from southwestern azimuths. We postulate that a sharp northeastward increase in Moho depth from the Inner Borderland (IB) to mainland southern California causes the anomalous phase velocities. Elastic forward modeling finds the travel times are fit well by a Moho that dips 65° to the northeast and flattens ~10 km southwest of the Newport-Inglewood fault zone. Constraining the felsic thickness of mainland crust to 28 km requires an 8 km thick layer with a P-velocity of 7 km/s beneath it, which could result from basal accretion of former Farallon ocean crust or magmatic underplating during Miocene volcanism. Forward models with a 65° Moho dip predict a P-to-s conversion with a phase velocity of ~5 km/s. Deconvolution of the array's mean P wave signal isolates a similar later arriving phase. The steep crust thickness transition supports a locally abrupt boundary to IB rifting. Our results highlight the utility of dense short-period arrays for passive imaging at near surface to uppermost mantle depths.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1002/jgrb.50370DOIArticle
http://onlinelibrary.wiley.com/doi/10.1002/jgrb.50370/abstractPublisherArticle
ORCID:
AuthorORCID
Clayton, Robert W.0000-0003-3323-3508
Additional Information:© 2013 American Geophysical Union. Received 14 April 2013; revised 23 August 2013; accepted 9 September 2013; published 3 October 2013. NodalSeismic LLC and Signal Hill Petroleum Inc. are thanked for providing data access, and we specifically thank Dan Hollis for his efforts in making the data available. We thank Craig Jones and Vadim Levin for constructive reviews. This research was supported in part by the Gordon and Betty Moore Foundation through the Tectonics Observatory at Caltech and by NSF grant EAR1214912. This is contribution #237 from the Tectonics Observatory. B.S. was also partially supported by the University of New Mexico.
Group:Caltech Tectonics Observatory, Seismological Laboratory
Funders:
Funding AgencyGrant Number
Gordon and Betty Moore FoundationUNSPECIFIED
NSFEAR-1214912
Caltech Tectonics ObservatoryUNSPECIFIED
University of New MexicoUNSPECIFIED
Subject Keywords:teleseismic imaging; Inner Borderland; seismic arrays; rifting
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Caltech Tectonics Observatory237
Record Number:CaltechAUTHORS:20140206-114352976
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20140206-114352976
Official Citation:Schmandt, B., and R. W. Clayton (2013), Analysis of teleseismic P waves with a 5200-station array in Long Beach, California: Evidence for an abrupt boundary to Inner Borderland rifting, J. Geophys. Res. Solid Earth, 118, 5320–5338, doi:10.1002/jgrb.50370.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:43704
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:06 Feb 2014 23:23
Last Modified:31 Jan 2017 20:45

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