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Dynamics of a phase change at the base of the mantle consistent with seismological observations

Sidorin, Igor and Gurnis, Michael and Helmberger, Donald V. (1999) Dynamics of a phase change at the base of the mantle consistent with seismological observations. Journal of Geophysical Research B, 104 (B4). pp. 15005-15023. ISSN 0148-0227. doi:10.1029/1999JB900065.

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The phase change model for the origin of the D″ seismic discontinuity is tested by comparing the results of convection modeling with seismic observations. We compute a number of global dynamic models that incorporate a phase change at the base of the mantle with different characteristics and transform the resulting temperature field and the distribution of phases to seismic velocities. Over 900 two-dimensional synthetic waveforms are computed for each of the models from which S, ScS, and Scd phases are picked. The distribution of the relative amplitudes and differential travel time residuals for these phases are statistically compared with the distribution of data from four well studied regions (northern Siberia, Alaska, India, and Central America) in a search for the characteristics of a phase transition that best match these seismic observations. We find that the best fit among the models considered is obtained for phase transitions characterized by a Clapeyron slope of ∼6 MPa K−1 and an elevation above the core-mantle boundary of ∼150 km under adiabatic temperature or 127 GPa and 2650 K on a (P,T) diagram. Dynamic models demonstrate that the value of Clapeyron slope and the density difference between the phases can have significant influence on the dynamics of plumes but probably only a minor influence on the dynamics of subducted slabs. We find that the thermal structure of subducted slabs can be important in giving rise to the seismic triplication; the strongest Scd arrivals in our models are observed in the area of subduction. The folding of the slab at the base of the mantle leads to patterns in differential travel time distributions consistent with seismic observations and suggests that the largest heterogeneity occurs at the top of the D″ layer or just above it. Analysis of the spatial autocorrelation functions of the differential travel time residuals suggests that their characteristic peaks reflect the patterns of slab folding and may provide constraints on the rheology of slabs at the base of the mantle.

Item Type:Article
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Gurnis, Michael0000-0003-1704-597X
Additional Information:© 1999 American Geophysical Union. Manuscript Accepted: 11 February 1999; Manuscript Received: 24 August 1998. This study was supported by NSF grants EAR9629279 and EAR9809771. This represents contribution 8550 of the Division of Geological and Planetary Sciences, California Institute of Technology.
Group:Seismological Laboratory
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Other Numbering System NameOther Numbering System ID
Caltech Division of Geological and Planetary Sciences8550
Issue or Number:B4
Record Number:CaltechAUTHORS:20130311-145952642
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Official Citation:Sidorin, I., M. Gurnis, and D. V. Helmberger (1999), Dynamics of a phase change at the base of the mantle consistent with seismological observations, J. Geophys. Res., 104(B7), 15005–15023, doi:10.1029/1999JB900065.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37450
Deposited On:11 Mar 2013 23:15
Last Modified:09 Nov 2021 23:29

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