Geoscience Reference
In-Depth Information
(a)
Alaska
(b)
Canada
SS
PP
SS
PP
Pds
200
300
400
500
600
700
800
900
200
300
400
500
600
700
800
900
220
240
X
X
390
390
400
410
410
520
520
520
640
650
660
660
720
810
90
°
a
b
60
°
c
30
°
d
0
°
180
°
240
°
300
°
0
°
60
°
120
°
180
°
Fig. 10.5
Stacks of SS and
PP precursors and receiver
functions in the same
location for regions in
(a) Alaska, (b) Canada,
(c) Asia and (d) Indian
Ocean. The SS and PP
precursors are stacked for
circular regions with a
radius of 10
◦
(Deuss, 2009).
Pds receiver functions are
for station FFC in Canada
and station ABKT in Asia
(Andrews & Deuss, 2008).
(c)
Asia
(d)
Indian Ocean
SS
PP
Pds
SS
PP
200
300
400
500
600
700
800
900
200
300
400
500
600
700
800
900
220
260
220
260
X
41
0
41
0
41
0
41
0
41
0
500
560
520
520
560
660
750
520
520
660
660
660
690
800
820
8
50
dependent. In general, it is more often observed
in long period seismic data, and has smaller
amplitudes and even becomes invisible in shorter
period data. In particular, the 410 km discon-
tinuity almost disappears in short period P
P
precursors (Xu
et al
., 2003), while it is seen con-
sistently in long period PP precursors (Flanagan &
Shearer, 1999; Chambers
et al
., 2005a,b). Benz and
Vidale (1993) initially suggested that both 410 and
660 were clearly visible in P
P
precursors. Later
studies, however, have shown that the '410' can
only sometimes be seen in P
P
precursors, but
in general it is not easily observed. This implies
that the Benz and Vidale (1993) observation of a
sharp 410 km discontinuity must have been an
exception, rather than the rule. If it is sharp, then
it is only sharp in a few regions and in general it
is mostly a broad discontinuity.
Mineral physics predicts a phase transition
in olivine from the
α
(olivine) to the
β
phase
