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0
5
10
R1
15
R2
20
25
30
(a)
+
-
+
-
0
DS
5
CS-DW
SE-CV
10
CS-R1
15
Figure 7.12 Numerical modeling results.
a) Split-spread seismogram, showing direct
wave (DW) and two reflections (R1, R2). b)
Corresponding electrogram, showing direct
field (DF), coseismic direct wave (CS-DW),
two coseismic reflections (CS-R1, CS-R2),
and seismoelectric conversions (SE-CV).
The star marks the location of the shot point,
and the marks at the top of panel b in this
figure indicate the locations of the two
dipoles used in the field experiment
together with polarity conventions.
CS-R2
20
25
30
-10
-5
0
5
10
Distance (m)
(b)
Step II. We simulate the total seismoelectric signals as
they would be received by the two dipoles in the field
experiment (Figure 7.13a; see dipole locations and
polarity conventions as annotated in Figure 7.12b), as
well as the coseismic and direct field contributions in
the total signal (Figure 7.13b). The total modeled seis-
moelectric signals for dipoles 1 and 2 are characterized
by strong, longer-period components that dominate
the first 4 ms, followed by many shorter-period signals
(Figure 7.13a and b). Given the dipole locations and
polarity conventions annotated in Figure 7.12b, we
confirm that seismoelectric conversions and coseismic
and direct field events are out of phase between dipoles
1and2(Figures7.13).Thisconfirmsthepolaritybeha-
viors inferred from field observations (Butler et al.,
1996), the theory (Haartsen & Pride, 1997), and numer-
ical computation (Haines & Pride, 2006), which are
first explained conceptually in Butler et al. (1996).
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