A low-velocity lamella in D″

Abstract

We investigate local variations of the P-wave velocity structure in the lower-most mantle (D″) beneath Western Siberia. Data of earthquakes in the Kurile Island region recorded at short-period stations of the Israel Seismic Network show a high-amplitude phase (PdP) after P which cannot be explained by standard Earth models. We present evidence that this phase is a reflection from a low-velocity lamella in D″. The best, locally valid, 1-D model consists of a low-velocity lamella 282km (±20km) above the core-mantle boundary with a thickness of 8km (±3km). The very high amplitudes of PdP cannot be reproduced by a 1-D model. The PdP observation reported here is a regional feature. The area north of it does not show a P-velocity anomaly, whereas further north positive jumps in P- and S-velocity have been documented. Our observation once more demosntrates the complexity of D″.