Evidence of Recent Thrust Faulting on the Moon Revealed by the Lunar Reconnaissance Orbiter Camera

Abstract

Lunar Reconnaissance Orbiter Camera images reveal previously undetected lobate thrust-fault scarps and associated meter-scale
secondary tectonic landforms that include narrow extensional troughs or graben, splay faults, and multiple low-relief terraces.
Lobate scarps are among the youngest landforms on the Moon, based on their generally crisp appearance, lack of superposed
large-diameter impact craters, and the existence of crosscut small-diameter impact craters. Identification of previously known
scarps was limited to high-resolution Apollo Panoramic Camera images confined to the equatorial zone. Fourteen lobate scarps
were identified, seven of which are at latitudes greater than ±60°, indicating that the thrust faults are globally distributed.
This detection, coupled with the very young apparent age of the faults, suggests global late-stage contraction of the Moon.

Full text

DOI: 10.1126/science.1189590
, 936 (2010);329 Science , et al.Thomas R. Watters
Lunar Reconnaissance Orbiter Camera
Evidence of Recent Thrust Faulting on the Moon Revealed by the
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Materials and Methods
Table S1
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3 May 2010; accepted 13 July 2010
10.1126/science.1191778
Evidence of Recent Thrust Faulting on
the Moon Revealed by the Lunar
Reconnaissance Orbiter Camera
Thomas R. Watters,
1
*Mark S. Robinson,
2
Ross A. Beyer,
3,4
Maria E. Banks,
1
James F. Bell III,
5
Matthew E. Pritchard,
6
Harald Hiesinger,
7,8
Carolyn H. van der Bogert,
7
Peter C. Thomas,
9
Elizabeth P. Turtle,
10
Nathan R. Williams
6
Lunar Reconnaissance Orbiter Camera images reveal previously undetected lobate thrust-fault
scarps and associated meter-scale secondary tectonic landforms that include narrow extensional
troughs or graben, splay faults, and multiple low-relief terraces. Lobate scarps are among the
youngest landforms on the Moon, based on their generally crisp appearance, lack of superposed
large-diameter impact craters, and the existence of crosscut small-diameter impact craters.
Identification of previously known scarps was limited to high-resolution Apollo Panoramic Camera
images confined to the equatorial zone. Fourteen lobate scarps were identified, seven of which are
at latitudes greater than T60°, indicating that the thrust faults are globally distributed. This
detection, coupled with the very young apparent age of the faults, suggests global late-stage
contraction of the Moon.
Most large-scale crustal deformation on
the Moon is directly associated with
the nearside mare-filled basins and is
expressed as contractional wrinkle ridges and ex-
tensional arcuate and linear rilles or graben (1,2).
Basin-radial and basin-concentric wrinkle ridges
occur in the basin interiors, whereas graben are
found at basin margins and in adjacent highlands.
The stresses that form this pattern of deformation
are the result of loading from uncompensated
mare basalt fill that induces subsidence and down-
ward flexure of the lithosphere (3). Lobate scarps
are tectonic landforms (4–7) that, unlike nearside
wrinkle ridges and graben, are generally found
outside of mare-filled basins in the highlands and
are the most common tectonic landform on the
farside (2). In contrast to basin-related wrinkle
ridges and graben, lobate scarps are relatively
small-scale structures. They are generally linear
or curvilinear asymmetric landforms with rela-
tively steeply sloping scarp faces and are often
segmented. Analogous large-scale lobate scarps
found on Mercury (8–11)andMars(12) can have
over a kilometer of relief; in contrast, known lunar
lobate scarps generally have a maximum relief of
<100 m (2,4–7) and proportionately smaller
lengths (less than tens of kilometers) (2,7). Based
on their morphology and crosscutting relations,
these structures are interpreted to be contractional
landforms resulting from low-angle thrust faulting
(4–7,13). Estimates of the fault displacement-
length scaling relations and the linkage between
individual scarp segments further support the
interpretation that lobate scarps are the surface
expression of shallow thrust faults (2). Although
many lobate scarps are found in the highlands,
some occur in mare basalts and others transition
from lobate scarps to wrinkle ridges (2,5,14).
Because most previously identified lobate scarps
could be easily identified only in high-resolution
Apollo Panoramic Camera images (13,15,16),
covering only a portion of the lunar equatorial
zone, their global spatial distribution was un-
known. The Lunar Reconnaissance Orbiter Cam-
era (LROC) Narrow Angle Cameras (NACs) and
the Wide Angle Camera (WAC) on the Lunar Re-
connaissance Orbiter (LRO) have obtained images
of known lobate scarps as well as previously
undetected scarps (n= 14). NAC high-resolution
images (0.5 to 2 m per pixel) and topography
derived from NAC stereo images allow the most
detailed characterization of the morphology and
relief of lunar lobate scarps to date.
The Lee-Lincoln scarp (~20.3°N, 30.6°E), just
west of the Apollo 17 landing site in the Taurus-
Littrow valley, is a well-known lobate scarp (17,18)
that cuts across the mare basalt-filled valley trend-
1
Center for Earth and Planetary Studies, Smithsonian In-
stitution, Washington, DC 20560, USA.
2
School of Earth and
Space Exploration, Arizona State University, Tempe, AZ 85251,
USA.
3
Carl Sagan Center, SETI Institute, Mountain View, CA
94043, USA.
4
NASA Ames Research Center, Moffett Field, CA
94035–0001, USA.
5
Department of Astronomy, Cornell Uni-
versity, Ithaca, NY 14853, USA.
6
Department of Earth and
Atmospheric Sciences, Cornell University, Ithaca, NY 14853, USA.
7
Institut für Planetologie, Westfälische Wilhelms-Universität,
48149 Münster, Germany.
8
Department of Geological Sciences,
Brown University, Box 1846, Providence, RI 02912, USA.
9
Center
for Radiophysics and Space Research, Cornell University, Ithaca,
NY 14853, USA.
10
Johns Hopkins University Applied Physics
Laboratory, Laurel, MD 20723, USA.
*To whom correspondence should be addressed. E-mail:
watterst@si.edu
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ing roughly north-south between the prominent
north and south highland massifs (Fig. 1A). To-
pography derived from NAC stereo images of the
Taurus-Littrow valley (figs. S1 to S3) indicates
that the northern segment of the valley-floor scarp
has a maximum relief of ~130 m and a narrow
low-relief rise associated with the scarp face (figs.
S2 and S3). The rise is more pronounced and has
greater relief (~20 m) on the southern segment of
the valley-floor scarp. The southern segment of
the scarp is also flanked by lobate low-relief foot-
hills with a maximum relief of ~40 m (Fig. 1A
and fig. S2). NAC images reveal a previously
undetected array of narrow shallow troughs in the
back-scarp area, west of the scarp face (Fig. 1B).
The small-scale troughs have maximum widths
of ~25 m and are typically 100 to 200 m in
length. Many of the troughs are shallow, with
relatively steeply sloping walls and flat floors.
We interpret these troughs to be small-scale frac-
tures and graben, indicating extension of the reg-
olith layer and the underlying mare basalts. These
graben are among the smallest-scale tectonic
landforms yet observed on the Moon. Assuming
that the antithetic normal faults of the graben
have equal fault-plane dips of ~60° (which is
typical for normal faults) and are rooted at the
base of the regolith, the regolith depth is esti-
mated to be on the order of the maximum width
of the graben. A depth of ~25 m is consistent
with the estimated regolith depth at the Apollo 17
landing site (~10 to 32 m), based on regional
seismic profile models (19). The orientation of
the graben varies from west-northwest to north-
east. Thus, some of the graben and fractures are
subparallel to the orientation of the scarp, where-
as others are nearly perpendicular to the scarp
(Fig. 1B). The most likely explanation for the
back-scarp fractures and graben is flexural bend-
ing of the valley-floor basalts, where bending
stresses cause extension and faulting of the up-
per regolith layer. Thrust faults are often accom-
panied by small-scale parasitic faults that result
from flexural bending and layer-parallel exten-
sion (14,20).
The Lee-Lincoln fault scarp (Fig. 1A) is not
confined to the mare basalts of the Taurus-Littrow
valley (4). To the north, the fault cuts across the
contact between the valley basalts and the high-
lands of North Massif, where it extends up-slope
for ~400 m before abruptly changing orientation
to the northwest, cutting along-slope for over 5 km.
The highlands scarp face is about 1 km from the
valley floor along much of its length and has a
maximum relief of ~5 m (fig. S4).
NAC images of the farside highlands Man-
del’shtam scarp (~6.9°N, 161°E), first identified
in Apollo Panoramic Camera images (7), show
that the scarp face is characteristically lobate (Fig.
2A). Like the Lee-Lincoln scarp, Mandel’shtam
has subsidiary scarps that form low-relief foothills
along some segments. The north-south–trending
scarp consists of several segments with a total
length of ~12 km. It is one of a series of scarps that
occur in the area near Mandel’shtam crater (7).
NAC images show that the northern terminus of
Mandel’shtam scarp appears to be made up of a
complex series of small scarps (Fig. 2A). These
small scarps are interpreted to be the surface
expression of splay faults.
So far, 14 previously unknown lobate scarps
have been revealed in NAC images (table S1).
These scarps occur in highland material. The north-
ernmost scarp, Rozhdestvenskiy-1, is found on a
ledge of rim material along the northern wall of the
42-km-diameter Rozhdestvenskiy crater (~87.5°N,
211.7°E). The east-west–trending scarp has a min-
imum length of ~5 km and has forefront subsidiary
low-relief scarps (Fig. 2B). The Rozhdestvenskiy-1
scarp terminates to the west at the rim of a ~330-m-
diameter impact crater. The smallest of the pre-
viously unknown lobate scarps is located in the
floor material of Slipher crater. This scarp (~48.3°N,
160.5°E) is divided into several segments and is
only ~3 km in length (Fig. 2C). The western termi-
nus of the east-west–trending Slipher scarp, like
the northern terminus of the Mandel’shtam scarp,
consists of a series of splay faults expressed by
multiple scarp segments. The vergent side of some
of these small fault segments is reversed from
south- to north-facing (Fig. 2C). Splay faults are not
restricted to the ends of lobate scarps. A previ-
ously unknown scarp (~74°S, 8.8°E) located near
Simpelius crater has a northeast-trending splay
fault that intersects the roughly east-west–trending
main scarp at an acute angle (Fig. 2D). The western
segment of the Simpelius scarp has multiple ter-
races that may be the expression of imbricate thrust
faulting (Fig. 2D). Multiple terraces suggestive of
imbricate faults are associated with other previ-
ously known lunar lobate scarps (2). The southern-
most previously unknown lobate scarp (~86.3°S,
54.7°E) is found near Shoemaker crater. The
northern segment of the north-northwest–trending
scarp appears to have relatively high relief and a
steeply sloping scarp face (Fig. 2E). The scarp
cutsalongaroughlyNW-SE–oriented linear fabric
and across an orthogonal NE-SW–oriented fabric
in the regolith.
The majority of the previously known lunar
scarps are located in the equatorial zone (Fig. 3).
Only 20% of the surface of the Moon was im-
aged by the Panoramic Cameras. It is likely that
less than 10% of this coverage had lighting ge-
ometry optimal for detecting the small-scale lobate
scarps (2,7). Of the 14 lobate scarps detected in
NAC images, seven occur at latitudes greater than
T60° (Fig. 3 and table S1). Three of these scarps,
Shoemaker and Rozhdestvenskiy-1 and -2, are
located very near the poles. Apparent gaps in the
longitudinal distribution of the scarps detected
with the NACs, particularly in the equatorial zone,
are probably due to limited image coverage in
those regions at the time of the survey. The oc-
currence of previously undetected lobate scarps at
high lunar latitudes, along with the distribution of
the mid- and low-latitude scarps on both the near-
side and farside, suggests that the thrust faults are
globally distributed (Fig. 3).
Lobate scarps appear to be very young,
among the youngest tectonic landforms on the
Moon (2,7,13). NAC images of known and
previously unknown scarps reveal crosscutting
relations with small-diameter impact craters. The
North Massiff segment of Lee-Lincoln scarp cross-
cuts impact craters with diameters as small as ~7 m
(Fig.4A).Mandel’shtam scarp crosscuts impact
Fig. 1. The Lee-Lincoln scarp in the Taurus-Littrow
valley. (A) The lobate scarp deforms mare basalts in
the Taurus-Littrow valley and extends into the high-
lands of North Massif where it cuts up- and along-
slope (LROC NAC image frame M104318871LE).
(B) Small narrow troughs in the back-scarp area of
theLee-Lincolnscarp(whitearrows).Thefigure
location is shown in (A) (LROC NAC image frame
M104318871LE).
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craters of various scales and with various states of
degradation (Fig. 4B). Assigning absolute ages to
scarps from crater counts is challenging, because
they are structural elements that have a limited
spatial extent. An upper bound on the age of the
scarp can be estimated based on the ages of the
stratigraphic units containing crosscut craters.
The crosscut craters are <50 m in diameter and
from estimates of relative ages of lunar craters
with various diameters and degrees of degrada-
tion, craters 50 m in diameter or smaller are Co-
pernican in age (21). The absolute age of the base
of the Copernican is estimated to be ~800 T15
million years (if defined by the age of Copernicus
crater) (22). Thus, the lunar scarps described here
are inferred to be <1 billion years old. This age is
consistent with the upper-bound age of lobate
scarps estimated by Binder and Gunga (7). The
Fig. 2. Known and previously undetected lobate
scarps. (A) The Mandel’shtam scarp. LROC NAC
frames M103460280LE and M103460280RE. (B)
Rozhdestvenskiy-1 scarp. The box shows the loca-
tion of the inset. [LROC NAC frames M105505727LE
and M107957296RE (inset)]. (C) Slipher scarp. Splay
faults mark the western terminus of the scarp (inset).
The box shows the location of the inset. LROC NAC
frames M103466592LE and M103466592RE. (D)
Simpelius scarp has a splay fault (white arrows) and
multiple fault-controlled terraces (black arrows). LROC NAC frames M106807247LE and M106807247RE. (E) Lobate scarp near Shoemaker crater. LROC NAC frames
M108891721LE and M108891721RE.
Fig. 3. The spatial distribution of
previously known (black dots) and
previously unknown (white dots)
lobate scarps on the Moon. The dis-
tribution of most of the previously
known lobate scarps correlates
with the limited Apollo Panoramic
Camera coverage of the equatorial
region. Lobate scarp locations are
plotted on a shaded relief map
merged with the Lunar Orbiter Laser
Altimeter global 64-pixel-per-degree
topographic model.
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most compelling evidence for a very young age
for the lobate scarps is their morphologically
crisp, undegraded appearance, transected and
disturbed meter-scale impact craters, and a lack
of superimposed of large-diameter (>400 m)
impact craters.
A major constraint on the initial temperature
and thermal evolution of the Moon are estimates
of radial contraction (23–26). The lack of dis-
tributed large-scale lobate scarp thrust faults
such as those on Mercury that express significant
radial contraction argues against secular cooling
of a completely molten early Moon (24,25).
Alternatively, the lack of large-scale thrust faults
(scarps >100 km in length and with >500 m of
relief) may be due to the accommodation of sig-
nificant contractional strain by the near-surface
regolith and an underlying pervasively fractured
zone (27). The relatively young, globally distributed
population of small-scale thrust faults described
here, however, may be evidence of late-stage
radial contraction of the Moon.
Alternatively, substantial tidally induced stresses
in the Moon, a tidally locked satellite under-
going orbital recession, may have been gener-
ated from relaxation of an early tidal bulge (28).
The resulting stresses are expected to cause con-
traction and thrust faulting in the region around
the sub-Earth point and its antipode and ex-
tension and normal faulting at the poles (28,29).
This predicted pattern is not consistent with the
observed spatial distribution of lobate scarps.
Tidal stresses raised solely by Earth are another
possible source of global stress; however, their
magnitude (a maximum of tens of kilopascals)
(30) is probably too low to initiate thrust faulting
(31). However, tidal stresses are a likely compo-
nent of the total stress that formed the thrust faults.
The areal contractional strain estimated with
the displacement-length (D-L) scaling relation of
previously known lobate scarps (2), with an up-
dated D-L value for the Lee-Lincoln scarp, is
~0.01% (32). This estimated contractional strain,
extrapolated to the entire surface, is equivalent to
a radius change of ~100 m and corresponds to iso-
tropic stresses due to radial contraction of <10 MPa
(2). The detection of previously unknown lobate
scarps at high latitudes is consistent with global
extrapolation of the regionally derived contrac-
tional strain.
Thermal history models for either a nearly or
totally molten early Moon, or an early Moon with
an initially hot exterior and magma ocean that
maintained a cool interior, predict late-stage com-
pressional stresses in the upper lunar crust and
lithosphere (6,24,25,33–35). The initially totally
molten model predicts stresses of up to 350 MPa
(7,33). Near-surface compressional stresses of
this magnitude might be expected to form a pop-
ulation of thrust-fault scarps comparable in scale
to the lobate scarps found on Mercury. Con-
versely, magma ocean thermal models that limit
the change in lunar radius to about T1kminthe
past 3.8 billion years (since the end of the period
of late heavy bombardment) predict compression-
al stresses of ~100 MPa or less (24,33). Although
a more accurate estimate of the contractional
strain expressed by the lobate scarps remains to
be determined, the value given here may only be
a lower limit if substantial horizontal shortening
has not been manifested (27). However, even if
the contractional strain is greater by a factor of 2,
the compressional stress due to radial contraction
is only on the order of ~15 MPa. Thus, in the
absence of substantial unexpressed contractional
strain, the observations reported here are con-
sistent with thermal history models that predict
low-level compressional stresses and relatively
small changes (1 km or less) in lunar radius. The
relatively young age of the faults suggests that
they formed during a recent episode of lunar radial
contraction. Earlier episodes of radial contraction
probably resulted in other populations of small-
scale thrust faults that are expected to be heavily
degraded and as yet unrecognized.
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(horizontal shortening of ~225 m), estimated with
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S1 and S3).
Fig. 4. Crosscutting relations between lobate scarps and impact craters. (A) The Lee-Lincoln scarp in
North Massif crosscuts an ~12-m-diameter impact crater (large white arrow and inset) and a ~7-m-
diameter crater (small white arrow and inset). Boulders are found along the scarp face (black arrows). The
figure location is shown in Fig. 1A. (LROC NAC frame M119652859LE.) (B) Degraded ~40-m-diameter
craters (lower white arrows) and a ~20-m-diameter crater (upper white arrow and inset) are crosscut by
the Mandel’shtam scarp. The figure location is shown in Fig. 2A. LROC NAC frames M103460280LE and
M103460280RE.
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36. We thank the three anonymous reviewers for
helpful comme nts that improved the manuscript. We
gratefully ac knowledge the Lunar Orbiter
Laser Altimeter team for the lunar topographic
model and the L RO and LROC engineers and
technical su pport person nel. This wor k was support ed
by the LRO Project, NASA grants NNX08AM 73G
and NNG07EK00C, and through Deutsches
Zentrum für Luft- und Raumfahrt grant 50
OW 0901.
Supporting Online Material
www.sciencemag.org/cgi/content/full/329/5994/936/DC1
SOM Text
Figs. S1 to S4
Table S1
15 March 2010; accepted 8 July 2010
10.1126/science.1189590
Drought-Induced Reduction in Global
Terrestrial Net Primary Production
from 2000 Through 2009
Maosheng Zhao*and Steven W. Running
Terrestrial net primary production (NPP) quantifies the amount of atmospheric carbon fixed by
plants and accumulated as biomass. Previous studies have shown that climate constraints were
relaxing with increasing temperature and solar radiation, allowing an upward trend in NPP from
1982 through 1999. The past decade (2000 to 2009) has been the warmest since instrumental
measurements began, which could imply continued increases in NPP; however, our estimates
suggest a reduction in the global NPP of 0.55 petagrams of carbon. Large-scale droughts have
reduced regional NPP, and a drying trend in the Southern Hemisphere has decreased NPP in
that area, counteracting the increased NPP over the Northern Hemisphere. A continued decline
in NPP would not only weaken the terrestrial carbon sink, but it would also intensify future
competition between food demand and proposed biofuel production.
Terrestrial ecosystems are a major sink in
the global carbon cycle, sequestering car-
bon and slowing the increasing CO
2
concentration in the atmosphere (1). Terrestrial
net primary production (NPP), the initial step of
the carbon cycle in which carbon is fixed as
biomass, increased from 1982 through 1999, in
part due to eased climatic constraints on plant
growth (2). The World Meteorological Organi-
zation (WMO), National Oceanic and Atmo-
spheric Administration (NOAA), and NASA all
reported that 2000 to 2009 was the warmest
decade since instrumental measurements of tem-
peratures began in the 1880s (3). We questioned
whether the warming climate of the past decade
continued to increase NPP, or if different climate
constraints were more important.
Between 2000 and 2008, CO
2
emissions from
fossil fuel combustion continued to increase at a
rate consistent with the average of the highest-
emissions family of scenarios, A1FI, used by the
Intergovernmental Panel on Climate Change in
the Fourth Assessment (1). Carbon-budget meth-
ods show that the land is becoming a stronger
carbon sink, whereas large uncertainties exist in
the partitioning of ocean and land carbon-sink
components (1,4). Satellite data can generally
provide realistic information on vegetation dy-
namics, including land cover change (5,6), dis-
turbances, and recovery (7), which may help to
reduce uncertainties in carbon-budget estimates.
In this study, we investigate terrestrial NPP and
climate variability over the past decade (2000 to
2009) by analyzing satellite data from the Mod-
erate Resolution Imaging Spectroradiometer
(MODIS) on board NASA’s Terra satellite and
global climate data.
We used the global MODIS NPP algorithm
(8) [see supporting online material (SOM) text
S1] to examine spatially explicit NPP changes
from 2000 through 2009. We used collection 5
(C5) 8-day composite 1-km fraction of photo-
synthetically active radiation (FPAR) and leaf
area index (LAI) data from the MODIS sensor
(9) as remotely sensed vegetation property dy-
namic inputs to the algorithm. Data gaps in the
8-day temporal MODIS FPAR/LAI caused by
cloudiness were filled with information from ac-
companying quality-assessment fields (SOM text
S2) (10). For daily meteorological data required
to drive the algorithm, we used a reanalysis data set
from National Center for Environmental Predic-
tion (NCEP) (SOM text S3) (11). A Palmer Drought
Severity Index (PDSI) (12) at 0.5° resolution was
used as a surrogate of soil moisture (13) to mea-
sure environmental water stress by combining in-
formation from both evaporation and precipitation
(SOM text S4). A lower PDSI generally implies a
drier climate.
Global NPP slightly decreased for the past
decade by –0.55 Pg C (Fig. 1). Interannual var-
iations of the global NPP were negatively cor-
related with the global atmospheric CO
2
growth
rates (correlation coefficient r=–0.89, p< 0.0006)
(Fig. 1) (14), suggesting that global terrestrial
NPP is a major driver of the interannual CO
2
growth rate. Carbon isotopic measurements have
indicated that the exchange of CO
2
with ter-
restrial ecosystems is the dominant cause of the
CO
2
interannual growth rate (15). Though NPP is a
part of carbon exchange between the land and
atmosphere, the strong correlation may imply that
the process of heterotrophic respiration depends
ultimately on the substrate supply from NPP (16),
Numerical Terradynamic Simulation Group, Department of Eco-
system and Conservation Sciences, the University of Montana,
Missoula, MT 59812, USA.
*To whom correspondence should be addressed. E-mail:
zhao@ntsg.umt.edu
Fig. 1. Interannual variations from 2000 through 2009 in anomalies of annual total global terrestrial
NPP (green circles) and inverted global atmospheric CO
2
annual growth rate [red squares and (14)].
Global average annual total NPP is 53.5 Pg C/yr.
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