Constraining seismic velocity and density for the mantle transition zone with reflected and transmitted waveforms

American Geophysical Union (AGU) - Tập 7 Số 10 - 2006
J. F. Lawrence1, Peter M. Shearer1
1IGPP Scripps Institution of Oceanography 9500 Gilman Drive, IGPP 0225 La Jolla California USA

Tóm tắt

We examine stacks of several seismic phases having different sensitivities to mantle transition zone structure. When analyzed separately, underside P and S reflections (PdP and SdS) are suggestive of very different structures despite similar raypaths and data coverage. By stacking the radial component of PdP rather than the vertical PdP, we show that this difference does not result from interference from other more steeply inclined phases such as PKP and Ppdpdiff. In general, stacks of P‐to‐S converted phases (Pds) appear to lack evidence of a 520‐km discontinuity when examined without other phases. When these phases and stacked topside P reflections (Ppdp) are analyzed jointly using a nonlinear inversion method, consistent but nonunique, seismological models emerge. These models show that a discontinuity at ∼653 km depth has smaller contrasts in density and velocity than found in most previous studies. A sub‐660 gradient can account for the majority of this difference. A 1.6 ± 0.5% P‐velocity contrast and a 2.2 ± 0.3% density contrast at ∼518 km depth without a S‐velocity contrast can explain the lack of a P520s, together with robust Pp520p and S520S phases. For models parameterized with a finite thickness for each discontinuity, the 410‐km discontinuity is consistently ∼3 times thicker than the 660‐km discontinuity.

Từ khóa


Tài liệu tham khảo

Aki K., 1980, Quantitative Seismology

10.1785/BSSA0810062504

Bassin C., 2000, The current limits of resolution for surface wave tomography in North America, Eos Trans. AGU, 81

10.1038/365147a0

10.1029/94JB00462

10.1029/1999JB900087

10.1029/2004JB003272

Cummins P. R., 1992, The 520‐km discontinuity, Bull. Seismol. Soc. Am., 82, 323

10.1111/j.1365-246X.2005.02682.x

Davies D., 1971, Vespa process for analysis of seismic signals, Nature, 232, 8

10.1126/science.1063524

Deuss A. J., 2006, The nature of the 660‐kilometer discontinuity in Earth's mantle from global seismic observations of PP precursors, Nature, 311, 198

10.1029/96JB03857

Durek J. J., 1996, A radial model of anelasticity consistent with long period surface wave attenuation, Bull. Seismol. Soc. Am., 86, 144, 10.1785/BSSA08601A0144

10.1016/0031-9201(81)90046-7

10.1785/BSSA0880030722

10.1126/science.274.5290.1179

10.1029/97JB03212

10.1029/97JB03212

10.1029/2001JB001194

10.1016/0012-821X(95)00215-X

Grand S. P., 1984, Upper mantle cross section from Tonga to Newfoundland, J. Geophys. Res., 76, 399

10.1029/2001JB000489

10.1016/S0012-821X(98)00027-2

10.1046/j.1365-246X.2003.01967.x

10.1111/j.1365-246X.1974.tb03623.x

10.1029/94GL02341

Husebye E., 1970, The origins of precursors to core waves, Bull. Seismol. Soc. Am., 60, 939, 10.1785/BSSA0600030939

10.1016/0012-821X(83)90073-0

10.1029/92JB00887

10.1111/j.1365-3121.1991.tb00863.x

10.1111/j.1365-246X.1995.tb03540.x

Koper K. D., 1999, Multimodal function optimization with a niching genetic algorithm: A seismological example, Bull. Seismol. Soc. Am., 89, 978, 10.1785/BSSA0890040978

10.1029/2005JB003973

10.1016/j.epsl.2005.10.030

10.1038/25972

10.1016/S0012-821X(00)00294-6

10.1029/2002GL015411

Mahfoud S. W.(1995) Niching methods for genetic algorithms Ph.D. thesis Univ. of Ill. Champagne.

Masters G., 2000, Earth's Deep Interior: Mineral Physics and Tomography From the Atomic to the Global Scale, 63, 10.1029/GM117p0063

10.1111/j.1365-246X.1996.tb06548.x

10.1126/science.1092485

Nguyen‐Hai, 1963, Propagation des ondes longitudinales dans le noyau terrestre, Ann. Geophys., 15, 285

10.1007/BF00874369

10.1029/JB094iB05p05787

10.1029/91JB01486

Ringwood A. E., 1975, Composition and Petrology of the Earth's Mantle

10.1029/96JB03179

10.1029/97JB02837

10.1029/91JB01592

10.1111/j.1365-246X.1993.tb01499.x

10.1029/95JB02812

10.1029/GM117p0115

10.1126/science.285.5433.1545

10.1038/355791a0

10.1029/96GL03371

10.1126/science.280.5367.1232

10.1038/35014589

10.1029/97JB00550

10.1038/356678a0

10.1016/0031-9201(77)90008-5

10.1029/96GL01261

10.1111/j.1365-246X.1984.tb01918.x

Ward S. N., 1978, Long‐period reflected and converted upper mantle phases, Bull. Seismol. Soc. Am., 68, 133, 10.1785/BSSA0680010133

10.1029/GM117p0215

10.1126/science.261.5127.1424

10.1111/j.1365-246X.1991.tb05700.x

10.1029/98GL00122

10.1029/2001JB000817

Thông tin
Thông tin xuất bản

American Geophysical Union (AGU)

Tập 7 Số 10

Thông tin tác giả