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Modelling D″ structure beneath Central America with broadband seismic data

Ding, Xiaoming and Helmberger, Donald V. (1997) Modelling D″ structure beneath Central America with broadband seismic data. Physics of the Earth and Planetary Interiors, 101 (3-4). pp. 245-270. ISSN 0031-9201. doi:10.1016/S0031-9201(97)00001-0.

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Deep South American events recorded at distances between 70° and 96° are used to constrain the lower mantle structure beneath Central America. Employing data from the TERRAscope, BDSN, IRIS and CNSN (Canadian National Seismic Network) broadband arrays, we obtain a 1-D shear model with a 200 km thick D″ layer with a 3% velocity jump at the top and a negative gradient within the layer from broadband waveform modelling of SH-polarized S, ScS, and Scd. The shear structure above D″ is similar to the Preliminary Reference Earth Model (PREM) (Dziewonski and Anderson, 1981. Preliminary Reference Earth Model. Physics of Earth & Planetary Interiors 25, 297–356) in terms of dT/dΔ and S-SKS differential times. SV synthetics for this model, assuming a PREM core, produce a satisfactory fit to the data, except at the larger ranges to the north, where the waveforms display rapid variation. This feature is indicative of lateral variation of the type suggested by Grand (1994), where the discontinuity becomes less well defined. Synthetics computed for a simplified 2-D cross-section through this structure produce the Scd phase and simple S at larger distances. While Scd is easily observed in the shear wave data, there is little evidence of its counterpart in the P data. By testing several models with different P-velocity jumps at the same depth as the D″ jump in shear structure, we conclude that the velocity jump must be less than 1%. In fact, PREM provides an excellent fit both in timing and waveform shapes and therefore we conclude that lower-mantle structure beneath Central America shows clear evidence for a discontinuity in S velocity but not in P.

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Additional Information:© 1997 Elsevier B.V. Received 12 August 1996; accepted 20 December 1996. We thank Hiroo Kanamori for his help with instrument corrections and his encouragement, and Ed Garnero for bringing these record sections to our attention and reviewing this manuscript. Also thanks to Don Anderson, Michael Wysession, Timothy Melbourne and Barbara Romanowicz for reviewing the manuscript. We also thank Steve Grand for providing us with his 3-D tomographic model and showing us how to use it and reviewing this paper. This research was supported by National Science Foundation grant EAR-93-16441. Contribution No. 5611, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California. This manuscript was prepared with AGUs LATEX macros version 4, with the extension package 'AGU ++' by P.W. Daly, version 1.5a from 1996/10/09.
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Caltech Division of Geological and Planetary Sciences5611
Issue or Number:3-4
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Official Citation:Xiaoming Ding, Donald V. Helmberger, Modelling D″ structure beneath Central America with broadband seismic data, Physics of the Earth and Planetary Interiors, Volume 101, Issues 3–4, May 1997, Pages 245-270, ISSN 0031-9201, 10.1016/S0031-9201(97)00001-0.
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ID Code:35712
Deposited On:28 Nov 2012 22:40
Last Modified:09 Nov 2021 23:17

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