Melbourne, Tim and Helmberger, Don (1998) Fine structure of the 410-km discontinuity. Journal of Geophysical Research B, 103 (B5). 10,091-10,102. ISSN 0148-0227 http://resolver.caltech.edu/CaltechAUTHORS:20121129-103321400
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The April 14, 1995, earthquake in western Texas (M_w 5.7) produced a strong topside reflection off the 410-km discontinuity which was recorded on a multitude of seismic arrays throughout the southwestern United States. Data from 394 vertical short-period and 24 broadband instruments provide dense coverage of this event from distances of 11° to 19° and provide a detailed look at the subcontinental 410-km structure. The salient features of this data set are (1) the strong dependence on wavelength of the 410-km triplication range, (2) the uniform amplitude ratio of the direct P and reflected P_(410) phases on both short-period and broadband recordings throughout the triplication, and (3) the abrupt termination of the short-period P_(410) phase at 13.3°. These features are best modeled by a composite discontinuity in which a sharp velocity jump of 3% is overlain by a linear velocity jump of 3.5% spread over 14 km. The interference of energy turning in the diffuse and sharp portions of this discontinuity structure reproduces both the long- and short-period triplication range and the step-like behavior of the P_(410) short-period amplitude, which cannot be reproduced with either a simple linearly diffuse or a purely sharp discontinuity. This composite structure produces a triplication range which depends on source frequency and has an apparent depth which depends on observation frequency. Additionally, this is the structure expected from mineralogical arguments for the α to β olivine phase transition.
|Additional Information:||© 1998 American Geophysical Union. Received 1 July 1997; revised January 1, 1998; accepted 12 January 1998. This research was supported by National Science Foundation grant NSF EAR-9316441 California Institute of Technology, Seismological Laboratory Contribution 6201.|
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|Official Citation:||Melbourne, T. and D. Helmberger (1998), Fine structure of the 410-km discontinuity, J. Geophys. Res., 103(B5), 10,091–10,102, doi:10.1029/98JB00164.|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||29 Nov 2012 18:45|
|Last Modified:||27 Dec 2012 03:05|
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