Geoscience Reference
In-Depth Information
Pressure
i
eld at
t
= 20 ms
Pressure ield at
t
= 16 ms
Pressure ield at
t
= 23 ms
0
10
Ba
ckground
Background
Background
0.5
0.5
0.5
20
Anomaly1
Anomaly1
A
Anomaly1
A
30
A
0.4
0.4
0.4
40
0.3
0.3
50
0.3
Anomaly2
60
Anomaly2
Anomaly2
0.2
0.2
0.2
70
80
0.1
0.1
0.1
90
100
0
0
0102030405060
0102030405060
0 102030405060
Offset (m)
Offset (m)
(a)
(b)
(c)
Offset (m)
Pressure ield at
t
= 25 ms
Pressure ield at
t
= 27ms
Electric potential distribution
0.25
0
0.2
10
Background
Background
Background
0.5
0.5
20
0.15
Anomaly1
A
Anomaly1
Anomaly1
A
30
0.1
0.4
A
0.4
40
0.05
0.3
0.3
50
0
Anomaly2
60
Anomaly2
−0.05
0.2
Anomaly2
0.2
70
−0.1
80
0.1
0.1
−0.15
90
−0.2
0
100
0
0102030405060
0102030405060
0 0 0 0 0 0
−0.25
Offset (m)
Offset (m)
(d)
(e)
(f)
Figur
e
6.3
Seismic beamforming and resulting electrical potential distribution.
(a
-
e)
Snapshots show the pressure field (coming from
the 46 seismic sources shown in Figure 6.1) focusing at point A. At
t
= 27 ms, the wave field interferes constructively at point
A producing a strong seismoelectric response that is recorded at the receiver electrodes.
f)
The distribution of the electrical potential
corresponds to the case where the seismic energy is focused at point A. The seismoelectric conversion at the time of focusing is
characterized by a strong dipolar behavior. (
See insert for color representation of the figure
.)
increase in amplitude due to the focusing of the pressure
field originating at the multiple seismic sources.
By applying this technique to a grid of points within the
survey area (i.e., by scanning the area point by point), we
can then use the electrical response to map the heteroge-
neities in terms of electrical and hydraulic properties of
the material without being able to distinguish what
factors are responsible for such heterogeneities. We can
also adjust and increase the resolution of our mapping
by scanning over a denser grid of points around certain
areas. The limitation (resolution) of the final map is
dictated by the wavelength of the seismic wave field with
amaximum resolution close to the dominant wavelength
divided by 8.
6.1.3 Results and interpretation
We focus the seismic energy on few points of interests,
and we record the electrical potential at the 46 electrodes
