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the other data types have simple circular Fresnel
zones and don't suffer from these complications.
10.2.3 Converted waves
This type of data includes conversion from P-to-S
waves, or vice versa, at the discontinuity (Figure
10.3). The compressional P arrival is used as a ref-
erence phase and the discontinuity phases arrive
as either precursors or postcursors (also called
'coda').
(c) ScS reverberations Finally, there are ScS
reverberations (see Figure 10.2c for an example
of one of the many potential ScS reverberations).
These are horizontally polarized shear waves
that reflect between the core mantle boundary
and Earth's surface. During these reverberations,
the energy is partly reflected by discontinuities
in the mantle and these discontinuities can
then be observed. The reflections lead to both
precusors and postcursors in a long time window
containing ScS, ScSScS etc. The details of this
technique are extensively described by Reve-
naugh and Jordan (1989) and they have used it in
subsequent studies of the discontinuity structure
in both upper and lower mantle (Revenaugh &
Jordan, 1991a,b; Revenaugh & Sipkin, 1994). This
technique has been used to study shallow upper
mantle discontinuities and the transition zone
discontinuities as well as the characteristics of
the core mantle boundary. ScS reverberations
have mainly been applied to determine mantle
structure in small corridors (10-50 epicentral
distance) between an event and receiver.
(a) P-to-S The conversions from P-to-S, also
called Pds phases, occur beneath the receiver,
so we speak of receiver functions (Figure 10.3a).
This technique was first introduced by Vinnik
(1977) and Vinnik et al . (1983) and is extensively
explained by Ligoria and Ammon (1999). Receiver
functions have been used in many global and
regionals studies ever since they were first
introduced, so only a small selection can be
discussed in this chapter. The topography on the
discontinuity can be determined with the use of
an array, see for example Thirot et al . (1998); Li
et al . (1998, 2000). Receiver functions, or P-to-S
conversions, only provide information about
discontinuities immediately below the receiver,
so they are very useful to determine the structure
beneath the continents but cannot be used easily
Converted waves
Converted and reflected waves
Pds receiver functions
Sdp receiver functions
Subduction zones
P wave
S wave
P wave
P wave
S wave
receiver
receiver
S wave
MOHO
MOHO
MOHO
410
source
660
S660p
P
S
P660s
p660P
S660P
P410s
S410p
(a)
(b)
(c)
Fig. 10.3 Ray paths for converted waves (a) Pds receiver functions and (b) Sdp receiver functions. (c) Also shown are
examples of ray paths for deep earthquakes in subduction, where a range of different reflected and converted waves
can be observed.
 
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