Abstract
This is the third paper in a four-part sequence that examines the nature of mantle layering using the multiple-ScS phases and internal reflections observed within the reverberative interval of SH-polarized seismograms. In this paper, migration techniques are applied to ScS reverberations to image discontinuities in shear impedance beneath a tectonically diverse study area that includes the western Pacific, Japan, the Philippine Sea, and Australasia. Between the M and 410-km discontinuities (Bullen's region B), the analysis reveals four reflectors. Overall, the results indicate an upper mantle where impedance layering varies substantially over a broad spectrum of scale lengths, but correlates with surface geology and plate structure down to at least 250 km (the L discontinuity), and perhaps to depths as great as 350 km (the X discontinuity). The lateral variability observed in region B reflectivity structure appears to be governed primarily by the thermal and chemical gradients related to continental deep structure and subduction. -from Authors
| Original language | English (US) |
|---|---|
| Pages (from-to) | 19,781-19,810 |
| Journal | Journal of Geophysical Research |
| Volume | 96 |
| Issue number | B12 |
| DOIs | |
| State | Published - 1991 |
Bibliographical note
Funding Information:1 The authors would like to thank the UK’s Arts and Humanities Research Council for their generous support of a four-year Standard Research Grant, Power, society and (dis)connectiv-ity in medieval Sardinia (ah/S006273/1), which allowed this article to be completed. We are also grateful to Don Ferdinando Loddo, Director of the Archivio storico diocesano ‘Mons. Ottorino Pietro Alberti’ in Cagliari for his permission to study and to photograph the lead seals of the Carte volgari.