Investigations to aid in the interpretation of seismic data obtained below the lunar surface are reported. Fine grained basalt with about 1.0% open core porosity was encapsulated under hard vacuum and measured. A Q value just under 2,000 at 0.5 kbar was achieved for a terrestrial analog of lunar basalt. In contrast to the modulus which increases by as much as 10%, the quality factor Q shows little or no change with pressure (a well outgassed sample maintains a high Q, whereas one exposed to laboratory atmosphere maintains a low Q). This result suggests that the absence of volatiles plays an important role in determining the q factor even at a depth of 10 km below the lunar surface

Tittmann, B. R.

English

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https://ntrs.nasa.gov/search.jsp?R=19770013027 2020-03-22T11:12:32+00:00Z
(bASA-CB-151215) INTPRNAL FRICTION Q FACTOR 	 H77-19971
NLASUR;&MBNIS IN LUNAR hOCKS Annual Report,
1 Feb. - 31 Dec. 1976 (Rockwell
International Scieace Center) 5 p IiC A02 1MF 	Unclas
A01	 CSCL 03B G3/91 20496 1	 ^h
February 1977
	 SC577.38AR
INTERNAL FRICTION Q FACTOR MEASUREMENTS
IN LUNAR ROCKS
ANNUAL REPORT NO. 3
For Period 02/01/76 thru 12/31/76
Contract No. NAS9-13846
General Order No. 577
Prepared for:
National Aeronautics and Space Administration
Lyndon B. Johnson Space Center
Science and Applications Directorate
Houston, Texas 77058
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NASA STI FACILITY. Rf^/w	 INPUT BRANCH N
B. R. Tittmann 
Principal Investigator
This work was sponsored by the National Aeronautics and Space
Administration. Reproduction in whole or in part is permitted
for any purpose of the United States Government.
Science Center
Rockwell International
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-77ACCESSION NO. 3. RECIPIENT'S CATAL )G NUMBER
4. TITLE (and SubNNe) S. TYPE OF REPORT 6 PERIOD COVERED
Annual Report
INTERNAL FRICTION Q FACTOR MEASUREMENTS 02/01/76 thru 12/31/76
IN LUNAR ROCKS - ANNUAL REPORT NO. 3 6. PERFORMING ORG. REPORT NUMBER
SC577.38AR
7. AUTHOR(,) B. CONTRACT OR GRANT NUMBER(,)
B.	 R.	 Tittmann NAS9-13846
9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT, PROJECT, TASKAREA b WORK UNIT NUMBERS
Science Center, Rockwell	 International
1049 Camino Dos Rios
Thousand Oaks, CA 91360
I t- CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE
National Aeronautics and Space Administration February 1977
Lyndon B. Johnson Space Center 13. NUMBER OF PAGES
Houston, Texas 77058 5
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17. DISTRIBUTION STATEMENT (of the abstract anterod)n Block ?0, if different from Report)
IS- SUPPLEMENTARY NOTES
19. KEY WORDS (Continue on reverse aide If necessary and Identify by block number)
Quality-factor Q, confining pressure, basalt, volatiles, attenuation,
seismic waves, terrestrial analog, adsorbed H2O, internal	 friction,
damping, absorption, vacuum, outgassing.
20. ABSTRACT (Continue on reverse side If necessary and Iden6'v by block number)
To aid in the interpretation of seismic data obtained below the lunar
surface we report here on measurements under confining pressures with the
sample encapsulated under hard vacuum.
	 Since partial crack closure would
be expected to occur already at low pressures,as evidenced by the well-known
and dramatic increases in velocity with increasing pressure in the 0.5 kbar
range, we have been concentrating our Q measurements in this range.	 In these
experiments we have been able to achieve a Q value just under 2000 at 0.5 kbar
DD I JAN 73 1473	 EDITION OF I NOV 65 IS OBSOLETE
4
UNCLASSIFIED
SECURITY CLASSIFICATI pN OF THIS PAGE.(W7hen Data Entered)	 P
Jed
--UNCLASSIFIED
MI IT I..LAbwt^I .M I IOM OY 1 MIS YA4Lf"n,,n U0,0 Cn,O,OO)
for a terrestrial analog of lunar basalt. We have also found that in contrast
to the modulus which increases by as much as 100" , the quality factor Q shows
little or no change with pressure, i.e., a well-outgassed sample maintains
a high Q, whereas one exposed to laboratory atmosphere maintains a low Q.
This result suggests that the absence of volatiles plays an important role in
determining the Q factor even at a depth of 10 km below the lunar surface.
UNCLASSIFIED
j'	 SECURITY CLASSIFICATION OF THIS PAGEOM.n Del. Lnl .d)	 fy
f
..	 t
Science Center
Rockwell International
SC577.38AR
QUALITY FACTOR Q UNDER CONFINING PRESSURE; B. R. Tittmann,
L. Ahlberg, and H. Nadler; Science Center, Rockwell International,
1049 Camino Dos Rios, Thousand Oaks, CA 91360
We have recently reported the discovery that small amounts of adsorbed
volatiles can have a profound effect on the Q of rocks and other porous
media (1). We have obtained room temperature Q values in excess of several
thousand in lunar sample 70215,85 and in strongly outgassed analogs of lunar
basalt. The effect is reversible in that re-exposure to laboratory atmos-
phere restores the Q to its original low value of Q ^ 100 (2). Experiments
carried out with a low-strain, low-frequency apparatus at 50 Hz show similar
increases of Q with outgassing, thus providing evidence that these changes
in Q can be expected to be important at seismic frequencies. These results
help explain the contrast between seismic data in the lunar and terrestrial
near-surface regions in terms of the absence and presence, respectively, of
adsorbed H2O.
To aid in the interpretation of seismic data obtained below the lunar
surface (3,4) we report here on measurements under confining pressures with
the sample encapsulated under hard vacuum. Since partial crack closure would
be expected to occur already at low pressures as evidenced by the well-known
and dramatic increases in velocity with increasing pressure in the 0.5 kbar
range - see, for example, ref. (5) - we have been concentrating our Q
measurements in this range. In these experiments vie have been able to achieve
a Q value just under 2000 at 0.5 kbar for a terrestrial analog of lunar
basalt. We have also found that in contrast to the modulus which increases
by as much as 10%, the quality factor Q shows little or no change with
pressure, i.e., a well-outgassed sample maintains a high Q, whereas one
exposed to laboratory atmosphere maintains a low Q. This result suggests
that the absence of volatiles plays an important role in determining the Q
factor even at a depth of 10 km below the lunar surface.
In the experiments, we have been using samples of fine-grained basalt
with about 1.0% open-pore porosity from an exposed dike in the Santa Monica
Mountains in Southern California. In the sample preparation vie have found
the following procedure most useful. After initial saw cuts, the samples
are gently ground into round cylinders 12.7 cm long, 1.0 cm radius. After
thorough cleaning and outgassing described previously (6), they are then
inserted into 4 mil wall seamless Cu tubing which is first heated so that
upon cooling it shrinks down tightly against the rock. The sheathed samples
and their end caps are then outgassed as before and mounted under dry He gas
in the Yielding chamber where they are held at 1 x 10- 5 torr for 12 hours.
At this point an electron beam is applied to seal the seam between the tube
and the end cap. Repeated exposure of the samples so prepared to confining
pressures show no deleterious effects on the seam and no anamolous decreases
in velocity due to leaks in the sheath, so that the vacuum inside the capsule
appears to be maintained intact. In order to lower the operating frequency
Of the encapsulated sample as much as conveniently , possible, the sample is
i
i
I01% Science Center
Rockwell International
SC577.38AR
end-loaded by using a solid Cu plu,
resonant frequency is lowered from
resonant vibration is now analyzed
the modulus is calculated from the
composite oscillator ana the known
unclad rock and Cu plugs.
for the end-cap. In this way, the
the 10 kHz to the 1 kHz range. The
in terms of a composite oscillator and
observed resonant frequency of the
or measured moduli and densities of the
Exoerimental Results. The ideal way to make a quantitative comparison
between a thoroughly ougtassed sample and a sample exposed to the atmosphere
is to make the measurements on the same sample under the two different
conditions. Although this appears difficult because of the vacuum encapsula-
tion process, we have found the following approach useful. We first encap-
sulate the sample in the outgassed State as described above, and proceed with
the pressure runs. Then the Cu end-caps are drilled, tapped, and, after the
sample is exposed for 48 hrs to laboratory air, are fitted with tightly
fitting Cu inserts which are threaded and bonded into place. Upon hardening
of the bond, the sample is checked for leaks and the pressure runs are
carried out.
Figure 1 gives an example of one of several experiments carried out for
the sample in torsional resonance and is typical for the pressure dependence
of the Q-factor in both the "outgassed" and "laboratory air exposed" states.
After initial gentle rises in Q with pressure, the curves are seen to level
off (with slightly lower Q at the higher pressures). This behavior is
completely different from the pressure dependence of the shear modulus which
in a characteristic manner shows a dramatic rise with pressure of up to 10%
over the same range of pressures. This result suggests that the partial
closing of cracks does not affect the Q nearly as strongly as it does the
stiffness of the rock and that adsorbed H2O is still likely to play a role
in determining the Q even at some depth below the surface. The highest Q
achieved in these runs was Q1800, which is nearly the same as the high
Q values previously achieved with well outgassed, unclad terrestrial analogs
at zero confining pressure.
References
(1) Tittmann, B. R., Housley, R. M., and Cirlin, E. H. (1974), Proc. Lunar
Sci. Conf. 5th, p. 2631.
(2) Tittmann, B. R., Curnow, J. M., and Housley, R. M. (1975), Proc. Lunar
Sci. Coif. 6th, p. 3217-3226.
(3) Dainty, A. M., Toksoz, M. N., and Stein, S. (1976), Proc. Lunar Sci. 	
l
Conf. 7th, p. 3057-3073.
(4) Nakamura, Y., Latham, G. V., Dorman, H. J., and Duennebier, F. K. (1976),
Proc. Lunar Sci. Conf. 7th, p. 3113-3121.
(5) Mizutani, H., and Newbigging, D. F. (1973), Proc. Lunar Sci. Conf. 4th,
P2601-2609.
(6) Tittmann, B. R., Ahlberg, L., and Curnow, J. (1976), Proc. Lunar Sci.
Conf. 7th, p. 3123.
I
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Rockwell Internatlonal
SC577.38AR
KAMAN RD BASALT MO, 1
DRIED IN VACUUM
O
O	 ^
O	 •	 O	 •
C7
EXPOSED TO ATMOSPHERE
jr	 C•	 •a	 • .
I O	 0.10
	
0.20	 0.30
PRESSURE (kbar)
Fig. 1 Quality factor Q dependence on confining pressur
analog of lunar basalt. Q measurements on Cu cl
established a background attenuation of Q- 1 <10-
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Internal friction Q factor measurements in lunar rocks

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