Vol.2, No.3, 155-159 (2010) Natural Science
http://dx.doi.org/10.4236/ns.2010.23025
Copyright © 2010 SciRes. OPEN ACCESS
Seismo-Microplasticity phenomenon in the rocks*
Eduard Innokentevich Mashinskii
Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, Novosibirsk, Russia; MashinskiiEI@ipgg.nsc.ru
Received 26 November 2009; revised 8 January 2010; accepted 30 January 2010.
ABSTRACT
The seismic records of borehole-to-borehole me-
asurements on frequency of 200 Hz in the mi-
crostrain range have been analysed. Microplas-
ticity manifestations caused by seismic wave
are detected on seismic records. It is the lad-
der-like stepwise change in amplitude course in
some parts of the seismic trace. The step dura-
tion (time plateau) presents the amplitude-
dependent time delay that shifts the arrival time
and protracts pulse front. The microplastic
process occurs owing to the anomalous re-
alignment of the internal stresses on the micro-
structural defects in “elastic” domain. Result is
the useful contribution for improvement of the
theory of wave attenuation in the rocks. It can
also be used in solving the applied problems in
material science, seismic prospecting, diagnos-
tics etc.
Keywords: Anelasticity; Deformation And Time
Delay; Anelastic Seismic Parameters; Amplitude
Dependence Of Wave Velocity And Attenuation
1. INTRODUCTION
Perfection of the wave attenuation mechanisms is up to
now one of main tasks in Earth’s sciences. For under-
standing attenuation mechanisms, the new knowledge is
necessary about the rock anelasticity. Viscoelastic model
of standard linear solid well describes the dispersion and
relaxation but insufficiently correctly explains, for ex-
ample, the amplitude-dependent effects. So, there are
some contradictions relative to character of amplitude
dependences of wave velocity and attenuation. There are
data about decrease of wave velocity and increase in
attenuation with increasing amplitude [1-4]. However,
there are also facts when increase in the strain amplitude
leads on the contrary to the increase in wave velocity
and decrease in attenuation [5-9].
Detection of the quasi-static rock microplasticity has
strengthened supposition about some unknown factor in
charge of the amplitude dependence of seismic parame-
ters [10-12]. It is necessary to mark that in Earth’s sci-
ences the microplastic anelasticity is not yet the gener-
ally accepted fact as against solid-state physics. In con-
trast to the viscoelasticity, microplasticity appears only
when stress reaches critical value. The microplastic strain
can increase and decrease, appear and vanish during
increasing stress. The amplitude-dependent effects in
rocks and quartz crystals were interpreted as indirect
attributes of microplasticity that is possible even on the
small strain amplitudes [13,14]. Assumption about mi-
croplasticity processes during seismic wave propagation
was also made in works [15-16].
The direct testimony of seismic microplasticity was
received in borehole-to-borehole measurements during
the amplitude effect study [17]. This paper describes mi-
croplasticity manifestations detected on the seismic traces
in result of the detailed analysis of the field materials.
2. EXPERIMENTS AND DATA ANALYSIS
The propagation of seismic pulse with diverse amplitudes
in the area between two boreholes was studied. The ex-
periments were performed in the Bystrovka research area.
The measuring instruments were mounted in two bore-
holes 110 mm in diameter and 12 m depth spaced 7 m. A
source was located in one of the boreholes and a receiver,
in the other. The source in borehole 1 and receiver in
borehole 2 were successively installed at depth of 2, 6,
and 10 m. Detailed description is in the work [17]. The
upper part of the section is comparatively homogeneous
and is composed of loams as far as a depth of a few tens
of meters. Rock is partially water-saturated as far as 8.5 m
with compressional wave velocity Vp = 240 300 m/sec.
After the depth – 9 m the wave travels in completely wa-
ter-saturated loams with Vp = 1500 m/sec.
The measurements were made in accordance with the
following procedure. The source and the receiver were
successively located at depths of 2, 6, and 10 m in the
diverse combinations. Such source-receiver configura-
tion enables to study the pulse propagation in the differ-
ent direction. Basic seismic records were made on the
location of source–receiver in the lateral (horizontal)
*This work was performed with the support of the Russian Fund of Fun-
damental Researches, grant N 05-09-00405.
E. I. Mashinskii / Natural Science 2 (2010) 155-159
Copyright © 2010 SciRes. OPEN ACCESS
156
-0.004
0.001
0.020.021 0.022 0.023 0.024 0.025
Time, sec
Amplitude, V
A1
A2
A3
A4
-0.04
-0.02
0
0.02
00.005 0.01 0.015 0.02 0.025
A1
A2
A3
A4
(
a
)
-0.0028
-0.0018
0.02184
A4
(c)
a
bc
a
cr
E
a
d
E
cd
(b)
Figure 1. Seismic traces recorded in the 6 m6 m “source-receiver” location on four amplitude values.
direction: 2–2, 6–6, and 10–10 m. On the short directions,
the seismic pulse propagated in the partially saturated
rock (6–6 m) and completely saturated rock (10–10 m).
The radiator of seismic signals consists of a set of pie-
zoelectric disks. The signal radiates through a liquid
spacer and hermetic elastic jacket contacting the borehole
wall. Predominant frequency of P- pulse is about 200 Hz.
The pressure receiver has the sensor of the piezoelectric
type (PDS-21) and, therefore, records compression ex-
tension waves. The receiver contacts the borehole wall
via an elastic spacer with a liquid. There is a preamplifier
with the amplification coefficients K = 100. The signals
were recorded in the digital form high-resolution during
of time (Bordo-B-421 system), and were processed on a
computer. The digitization time is 8 microseconds and 40
microseconds, the amplitude range is approximately (4
50) × 10-8. The discrete amplitude change was fulfiled in
a closed cycle, from the minimum to the maximum value
and back (Amin Amax Amin, 4 values upward and
3 values downward).
Some parts of seismic trace have the form of ladder
with the horizontal steps or plateau. The steps are evi-
dence of interruption in the stress course and the pres-
ence of the time delay and deformation delay. The pre-
sumable reason of such effect is microplasticity caused
by seismic wave. The signs of microplasticity were de-
tected on many seismic records. The typical fragments
from seismic traces with seismic microplasticity mani-
festations (SMM) are presented on Figures 1 and 2.
SMM take place for signals with low and high intensity,
i.e. small and great deformation rate.
A SMM example with small strain rate is shown in
Figure 1. Here are presented four seismic traces recorded
on four amplitude values in the 6–6 m “source-receiver”
location. Change in amplitude value during defined time
interval determines the amplitude steepness RA/t. The
amplitude value Ai is determined by number n of the
amplitude quantization steps (Aqu): Ai = n Aqu during
one time quantization step, tqu. The amplitude steepness
is calculated as RA/t = n Aqu/ tqu, i.e. it is determined by
way of number n. Thus, steepness is n = 2 for ampli-
tudes A1, A2 and n = 5 for amplitudes A3, A4. The step
length determines the time delay duration. The time de-
lay in this case is from one tqu to more than ten of tqu. On
the recordswith the small amplitude steepness, tqu is
equal 40 microseconds.
A SMM example of amplitude change with high rate
(n = 50 and n = 100) is presented in Figure 2. This re-
cord concerns the case when both source and receiver
were located at the depth of 10 m. Here the traces are
presented for the upward and downward amplitudes. In
principle, there is close coincidence in the form of the
repeated traces although there are some nuances (see
inset b). The delay duration in this case is tens of micro-
seconds (tqu = 8 microseconds).
The time delay changes the arrival time (see inset c in
Figure 2) and can also influence on the wave front dura-
tion. In the same time, duration of the time delay depends
Eab
E. I. Mashinskii / Natural Science 2 (2010) 155-159
Copyright © 2010 SciRes. OPEN ACCESS
157
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
00.001 0.002 0.003 0.004 0.005 0.006
Time, sec
Amplitude, V
A1-up
A2-up
A3-up
A4-up
A3-down
A2-down
A1-down
-0.46
-0.36
-0.26
-0.16
-0.06
0.00568 0.00608 0.00648
A1-up
A2-up
A3-up
A4-up
A3-down
A2-down
A1-down
(a)
-0.27
-0.24
-0.21
0.006008 0.006208
A2-up
A3-up
A4-up
A3-down
A2-down
(b)
-0.1
-0.05
0.0043 0.0045
A1-up
A2-up
A3-up
A4-up
A3-down
A2-down
A1-down
(c)
Figure 2. Seismic traces recorded on 4 upward and downward amplitudes in the location of “source– receiver” on 10 m.
on strain amplitude. Therefore, the amplitude variations
can lead to the pulse parameters change. The experi-
ments show that the increase in strain amplitude causes
the displacement of an arrival time towards smaller time.
The protracting of the wave fronts caused by time delay
occurs in complex way. In the present time, could say
that the intensity increase in wave shows the greater ex-
pressiveness of SMM. For the study of these effects, the
conducting of the special experiments is needed.
3. DISCUSSIONS
Data about dynamic microplasticity in solid states and
quasi-static microplasticity in the rocks confirm possi-
bility of SMM conditioned by seismic wave. The strains
level in static test and in seismic wave in the moderate
amplitude range is approx selfsame (10-6 10-5). The
difference in the strain rate is not obstacle for the mi-
croplasticity process as a physical mechanism in both
cases is, seemingly, the same. The point is that mi-
croplasticity is the frequency-independent (time-inde-
pendent) process at least on seismic frequencies. Nu-
merous data testify about prevalence of microplasticity
effects in metallic materials, alloys, ceramics, thin-film
materials and other solid states in the acoustical and
low-frequency range [18,19]. Avowed feature of medium
with microplasticity is the dependence of wave attenua-
tion on strain amplitude. As regards rock microplasticity,
here there are the obvious gaps in one's knowledge. In-
asmuch as the direct manifestations of rock microplas-
ticity have been established only during quasi-static
stress in lab conditions (measurements on the samples)
[10], any study of rock microplasticity under dynamic
force is the considerable advancement in these investiga-
tions. Especially importantly, when it concerns the dy-
namic research in natural conditions.
In itself the physical experiment in situ for the pur-
pose of microplasticity detection in the rocks triggered
by seismic wave is original. In this experiment, natural
medium in which propagation of seismic pulse occurs is
test subject. It is unlimited medium in contrast to labo-
ratory samples of small size. This medium consists of
the dry and water-saturated rocks. It determines the ex-
periment specificity. Microplasticity detection became
possible also thanks to the using of the high-resolution
seismic record in the time domain (microseconds) in
which there is no need for the usual record of seismic
signals. Besides, new information and results originality
have been obtained thanks to the sounding by the dif-
ferent-intensity pulses upward and downward. Mi-
croplasticity amount depends on the energy level applied.
One can surmise that with increasing wave intensity
occurs the switching on the sources of microplasticity
with the multi-level hierarchy.
SMM can be explained in the following way. Inas-
much as the piezoelectric receiver registers the change
in dynamic stress (strain) with time, the flat steps on
the trace mean the brief interruption in the course of
158 E. I. Mashinskii / Natural Science 2 (2010) 155-159
Copyright © 2010 SciRes. OPEN ACCESS
stress. Such stress stop supposes similar stop on the
stress-strain curve that can occur owing to the mi-
croplasticity process. Total strain = e + µ + v-e in
the small-strain range consists mainly of elastic and
microplastic component (e + µ), as viscoelastic com-
ponent v-e is comparatively small [10,11]. During
loading (or unloading), both components have own
contribution to the total strain. The stop in the course of
stress occurs when the stress reaches some critical
value σcr (for example, in the point b see inset (b) in
Figure 1). At that moment, the redistribution of con-
tribution between components occurs thus that contri-
bution of the microplastic component become pre-
dominant. In the extreme case, the strain increment
occurs only thanks to microplasticity as the increment
due to the elastic deformation does not occur at all [10].
Therefore, the yield process is also possible. The re-
grouping in components occurs thus that effective
modulus Eab and accordingly the stress and strain re-
main invariable during interval bc. It is possible ow-
ing to the distinctive feature of rock microplasticity that
can both increase and decrease or even vanish during
stress. In the point c after delay, the stress recom-
mences own course with the same modulus. There is
the hierarchical set of the diverse critical stresses that
switch on the microplasticity sources when amplitude
increases (decreases). Thus, seismic wave switches on
the process of the anomalous redistribution of stresses
and strains and respectively adequate to it process of
the structural realignment in the rock. It takes a definite
time that leads to deformation delay. In order to ex-
clude the instrumental factor in appraisal of SMM, the
amplitude error of analog-digital converter is checked.
Testing of this device shows that the own error in pla-
teau duration does not exceed 2 microseconds in the
broad range of the amplitude steepness.
Similar deformation stops caused by microplasticity
were detected in C60 single crystals [20]. It is shown that
magnetic field manipulations lead to a change in the
strain rate, the decrease in the rate being accompanied by
a brief interruption of deformation. The deformation
delay (incubation period) was observed also in the
high-temperature superconductors, possessing by mi-
croplasticity [21]. Delay appearance is bound with pres-
ence of opposite internal stresses for decrease of which
time is required. The wave attenuation mechanism in the
rock with microplasticity (referring to the experiments
[10]) is theoretically substantiated also in work [22]. As
regards the mechanism of wave attenuation, the combi-
nation of known mechanisms is possible, for instance, as
the hybrid relaxation-hysteresis mechanism [12]. It must
not be ruled out also the acoustoplastic effect in the
rocks as in metals and alloys [23]. The instance of stress
jumps marked on seismic record evokes the great cau-
tion in interpretation of this effect, and therefore for the
time being, we do not examine this question.
4. CONCLUSIONS
The result of this work is the new knowledge about na-
ture of propagation of the mechanical oscillations in the
Earth. The unnoticed heretofore presence in seismic re-
cord of microplasticity manifestations was detected
thanks to the high-resolution signals measurements. The
quasi-static microplasticity of the rocks, dynamic mi-
croplasticity of many solid states denoted the prospect of
our search. The dynamic microplasticity in the rocks
definitely is bound with critical amplitudes but its de-
pendence on strain rate is not yet established. One may
surmise data about rock microplasticity will enlarge the
comprehension of some known effects that had not for-
merly of the satisfactory physical explanation. We see it
now in the delay effect of the arrival time and the pulse
shortening-widening.
As stated above, the nature of microplasticity in the
rocks can coincide with known mechanisms in the solid
states (for instance, dislocation microplasticity) or to be
quite other (quasi-microplasticity). In the last case in
spite of the difference in mechanism, the microplasticity
manifestations can be the same as in usual solid states.
This question requires subsequent clarification. Microplas-
ticity affects the little-known anelastic processes of the
small-amplitude wave propagation. The new knowledge
about nonlinear-anelastic processes during wave propa-
gation will help in discovery of new diagnostic indica-
tions permissive to increase the efficiency of seismic
method for search of oil-gas deposits.
5. ACKNOWLEDGMENT
The author thanks G.V. Egorov for the help in the experimental work.
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