Broad-Band Converted Phases from Midmantle Discontinuities
Lev Vinnik, Fenglin Niu, Hitoshi Kawakatsu
Earth, Planets, and Space (OHP special issue), 50. 987-997, 1998.
Abstract
A technique for detecting intermediate-period (6 - 12 s)
SdP phases converted from S to P at a depth d in
the source region is described.
Previously, these phases were detected in short-period
array recordings of deep events.
The main idea of our technique is to deconvolve the vertical
component of a single record by the S waveform,
and to stack the deconvolved components of a number of records,
with appropriate time-shift corrections accounting for the difference of
epicentral distance.
Using this technique, the phases converted from discontinuities
at around 660 km, 860km, 1070 km, and 1170 km depths beneath
Sunda arc are detected at seismograph stations in central and
eastern Asia.
Our data on '1070 km' discontinuity are very consistent with
those inferred from short-period recordings of the same events at
the J-array in Japan (Niu and Kawakatsu 1997),
but favour a few different discontinuities,
rather than one with a strongly variable depth.
When compared with a tomographic model of the mantle for the same region,
our data suggest that '1070-km' discontinuity may act as a
barrier for the downgoing lithospheric slabs.