Cabral cano subsidencemexicocity

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Geological Society of America Bulletin

Space geodetic imaging of rapid ground subsidence in Mexico City
Enrique Cabral-Cano, Timothy H. Dixon, Fernando Miralles-Wilhelm, Oscar Díaz-Molina, Osvaldo
Sánchez-Zamora and Richard E. Carande

Geological Society of America Bulletin 2008;120;1556-1566
doi: 10.1130/B26001.1

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Notes

© 2008 Geological Society of America



Enrique Cabral-Cano†
Departamento de Geomagnetismo y Exploración, Instituto de Geofísica, Universidad Nacional Autónoma de México, Ciudad Universitaria,
México D.F. 04510, Mexico
Timothy H. Dixon
Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, 4600 Rickenbacker Causeway, Miami, Florida 33149, USA
Fernando Miralles-Wilhelm
Department of Civil and Environmental Engineering, Florida International University, 10555 West Flagler Street, Miami, Florida 33174, USA
Oscar Díaz-Molina
Departamento de Geomagnetismo y Exploración, Instituto de Geofísica, Universidad Nacional 10 Autónoma de México, Ciudad
Universitaria, México D.F. 04510, Mexico
Osvaldo Sánchez-Zamora
Departamento de Sismología, Instituto de Geofísica, Universidad Nacional Autónoma de México, Ciudad Universitaria, México D.F.
04510, Mexico
Richard E. Carande
Neva Ridge Technologies, 4750 Walnut Street, Suite 205, Boulder, Colorado 80301, USA

ABSTRACT INTRODUCTION in the Mexico City metropolitan area due to
ground subsidence. Monitoring of the spatial
Since the late 1950s, several areas of Mex- Many of Earth’s urban and suburban areas and temporal patterns of surface deformation
ico City have undergone accelerated ground are subsiding due to excess withdrawal of flu- associated with fluid withdrawal is an important
subsidence and have developed associated ids, principally water, but also petroleum, natu- first step, and it is the focus of this paper.
fracturing and faulting. New interferometric ral gas, and geothermal fluids (Poland, 1984). No current single technique gives complete
synthetic aperture radar (InSAR) and global While most subsidence rates are relatively low temporal and spatial sampling of subsidence.
positioning system (GPS) data indicate that (<10 mm/yr) and local (<100 km2), much higher Here, we describe the recent subsidence of
rates of current land subsidence in Mexico rates over larger areas are possible, increasing Mexico City due to groundwater withdrawal
City exceed 350 mm/yr. These rates are close the risk of flooding, damage to infrastructure using a combination of interferometric synthetic
to historical maximum levels of the mid-twen- from differential subsidence, and damage to the aperture radar (InSAR) for high spatial resolu-
tieth century, when mitigation efforts were fluid reservoirs by overpumping and permanent tion and global positioning system (GPS) data
first undertaken to reduce damage to urban porosity loss. for improved temporal information and cali-
infrastructure. The locus of maximum subsid- Since the late 1950s, several areas of Mexico bration. We use a remote-sensing approach to
ence has shifted from its historical location in City have undergone accelerated ground subsi- define regions where large differential subsid-
the old city center to the east. Correlation of dence and associated shallow fracturing and ence results in large strain gradients, which thus
our InSAR results with seismically mapped faulting. These faults have mainly developed on require closer monitoring.
stratigraphic units suggests that subsidence is the piedmont and talus deposits of older Qua-
primarily controlled by compaction of Quater- ternary volcanoes and other volcanic structures GEOLOGIC AND HYDROLOGIC
nary lacustrine clays and silts. We also evalu- and have continuously damaged housing, utility BACKGROUND
ate spatial gradients in subsidence and suggest works, and other urban infrastructure. The inte-
that this, rather than subsidence magnitude, is grated economic damages of this process are The southern portion of the Basin of Mexico
the key factor in risk assessment. Subsidence large, rivaling those of a strong earthquake, but (Fig. 1) includes a low-relief lacustrine plain,
represents a major geologic risk for Mexico they have received less attention because of the formerly covered by shallow water bodies and
City and imposes serious constraints to any longer time frame. The economic consequences wetlands, commonly referred to as the Val-
further urban development. of subsidence, while large, are generally fac- ley of Mexico. This area at present has several
tored into yearly maintenance budgets rather small lakes, including Texcoco, Zumpango, and
Keywords: subsidence, interferometry, GPS, than accounted for as unique natural disasters Chalco; the latter was completely drained at the
SAR, Mexico Basin. at a single point in time. As these integrated turn of the twentieth century. These lakes, along
costs grow, it becomes increasingly important with the Xochimilco canal system, are remnants
†
E-mail: ecabral@geofisica.unam.mx. to assess the extent and magnitude of damage of a large water body that encompassed about

GSA Bulletin; November/December 2008; v. 120; no. 11/12; p. 1556–1566; doi: 10.1130/B26001.1; 10 figures.

For permission to copy, contact editing@geosociety.org
1556
© 2008 Geological Society of America


one-fourth of the total surface of the basin sev- to compaction of lacustrine shales and surface 1988; Ghiglia and Pritt, 1998). In the interfero-
eral thousand years ago. subsidence. Drilling for groundwater started in grams (Fig. 2), one color cycle represents 28 mm
The Mexico City metropolitan area, located the 1850s. Subsidence was eventually recog- of range change (one half the SAR wavelength)
in the southern section of the Mexico Basin, is nized as a serious problem (Gayol, 1925), but in the line of sight direction between the satel-
a heavily populated urban area with ~17 million the link between groundwater extraction and lite and ground (23° from vertical in the case of
inhabitants (INEGI, 2000). Originally named clay compaction was only recognized later ERS1/2 and 15°–45° for ENVISAT_ASAR).
Tenochtitlán, the capital of the Aztec empire, it (Carrillo, 1948). By 1952, total subsidence Although this range change is usually interpreted
was built over the former Lake Texcoco, parts of (1891–1952) had reached 6.0 m in the down- as vertical motion when considering fluid with-
which survive east of the Mexico City metropol- town area (CHCVM, 1953). More recent sur- drawal, reservoir contraction may induce hori-
itan area, in a high (2200 m elevation), closed veys show up to 2.5 m of additional subsidence zontal motions as well. If the motion is purely
basin ringed by mountains that can exceed 5000 between 1952 and 1973. Other studies show an vertical, 28 mm of range change corresponds to
m elevation (Fig. 1) and that provide natural average subsidence rate of 90 mm/yr for the a true vertical motion of 30.4 mm. We then reg-
recharge of basin groundwater (Ortega and 20 yr period 1965–1985 in the downtown area istered the SAR interferogram to high-resolution
Farvolden, 1989). The unusual location poses (CAVM, 1975; Figueroa-Vega, 1984; Ortega et optical image data from the Advanced Space-
technical challenges for hydraulic management. al., 1993). The decrease in subsidence rates after borne Thermal Emission and Reflection Radi-
Flooding in the sixteenth and seventeenth cen- 1965 reflects conservation measures instituted ometer (ASTER) to improve georeferencing
turies led to artificial opening of the basin and in the 1950s and 1960s, which included capping and facilitate feature matching, for example, the
construction of other hydraulic works in the wells near the city center. location of InSAR fringes with respect to water-
late 1700s to divert flood water. Since then, a Consequences of the subsidence process are well locations or major street intersections.
major hydraulic management network has been costly. Water sewage works must be constantly GPS analysis and error estimation proce-
built and periodically upgraded, maintaining the upgraded due to loss of gradient, and transi- dures follow Dixon et al. (2000) and Sella et al.
flood-control function but also drastically reduc- tional areas between lacustrine beds and slope (2002). Permanent station UIGF (Ciudad Uni-
ing natural groundwater recharge. deposits are prone to severe differential subsid- versitaria) on the southwestern margin of the
Mexico Basin stratigraphy is well described ence, damaging housing and urban infrastruc- Mexico City metropolitan area has been occu-
(Schlaepfer, 1968; Mooser, 1975; Vázquez- ture. However, the regional extent and spatial pied since 1997. Station AIBJ (Mexico City
Sánchez and Jaimes-Palomera, 1989). GODF variation of subsidence, and seasonal and lon- International Airport) was occupied for a total
(2004) presented the most recent geotechnical ger-term variations, are not well monitored or of 10 twenty-four hour sessions at the end of
classification of the main surface and near-sur- understood, hampering effective mitigation. the dry season (May–June) between 1995 and
face units: a hard rock unit, a transitional unit, 2001. A permanent GPS station located on the
and a lacustrine unit. The hard rock unit (Unit I DATA PROCESSING center of the historic downtown was installed
in Fig. 2) corresponds to the slopes of surround- April 2004, and more recent permanent GPS
ing mountain ranges and includes basaltic lava InSAR has been used to study a variety of stations (MRRA, MPAA, and MOCS) have
flows and pumiceous tuffs and sandy/silty beds surface deformation processes, including sub- continuously recorded data since early 2005 in
with a high percentage of gravel. The transi- sidence from groundwater withdrawal, and the order to monitor subsidence with high temporal
tional unit (Unit II, Fig. 2) is a slope deposit; it technique is well described (e.g., Massonnet et resolution. We fit a weighted least-squares line
represents the transition between the lacustrine al., 1997; Galloway et al., 1998, 1999; Galloway to the GPS position data for each site to derive
beds and rock outcrops. It consists of progres- and Hoffman, 2006; Fielding et al., 1998; Ame- the average velocity and uncertainty over the
sively thicker sedimentary deposits overlying lung et al., 1999). We used Synthetic Aperture entire observation period, and also considered
the uppermost clay-rich lacustrine beds with Radar data from the European Remote Sensing subsidence over shorter intervals.
interbedded lacustrine and alluvial deposits. The Satellite (ERS) 1 and 2 (pre-2001) and from the GPS data also allow calibration of InSAR
lacustrine unit (Unit III, Fig. 2) includes depos- Advanced Synthetic Aperture Radar (ASAR) measured subsidence. For example, the unad-
its from former Lake Texcoco, mainly soft and onboard the Environment Satellite (ENVISAT; justed 1996 interferogram agrees well with both
compressible silts and clays with relatively low 2003 and later). ERS-1/2 data collected prior to GPS sites, implying minimal orbit error and/or
permeability. A large percentage of the modern 2001 was used, but many interferometric pairs atmospheric delay effects in this data set. On
city is built over these beds, reflecting the his- yielded poor coherence, in some cases, due to the other hand, the 1999–2000 interferogram
tory of urban development since the Spanish the long time span between passes. Best results predicts subsidence at UIGF 55 mm below that
conquest. Unit III ranges up to 80 m in thick- were obtained with image pairs spanning rela- indicated by the GPS analysis at this site. The
ness and overlies coarser, more permeable beds tively short time spans. The following discus- InSAR-derived profile in Figure 3 is adjusted
that comprise the main aquifer, mainly alluvial sion is based on SAR images acquired in 1996 based on the UIGF data, allowing an InSAR-
sands and gravels, as well as Pleistocene-Recent (1 and 2 February and 16 May), 1999, 2000 (7 based estimate of subsidence within the study
volcanic rocks in the depth range 100–400 m. January and 17 March), 2003 (10 October and 31 area relative to UIGF.
The Mexico City metropolitan area con- December), and 2005 (15 April and 24 June).
sumes over 65 m3/s of water (JACMCW, 1995), Topography data from the Shuttle Radar SUBSIDENCE ANALYSIS
and more than 70% of it comes from the aqui- Topography Mission (SRTM) was used for the
fer beneath the city through a system of more topographic correction. We assumed a constant The InSAR data (Fig. 2) suggest significant
than 380 water wells. The larger basin has more rate of surface change to make a first-order cor- range change across most of the Mexico City
than 630 wells. In a typical year, consumption rection for this effect and used a phase unwrap- metropolitan area in the 1996, 1999–2000,
exceeds recharge, lowering the water table by ping algorithm to convert ambiguous fractional- 2003, and 2005 data sets. However, assuming
0.1–1.5 m/yr, reducing pore fluid pressure in phase measurements to continuous phase these changes represent real surface displace-
the aquifer and overlying aquitard, and leading corresponding to range change (Goldstein et al., ment, do they indicate purely vertical motion, or

Geological Society of America Bulletin, November/December 2008 1557

Cabral-Cano et al.

20°00′ N

30 N

20

-110 -100 -90

Sierra de Guadalupe

Figure 1. Location map and
shaded digital elevation model
of study area in central Mexico.
Rectangle shows the coverage of
Sierra de Las Cruces Mexico City images in Figure 2.
Sierra Sta. Catarina

Sierra Nevada

0 8 16
Popocatpetl volcano
4 12 20 km
19°00′
99°40′ 98°20″
5400 0m

19°15′ N
N
Lake
Texcoco N 1996 N 2000
Tlalnepantla Unit I

Unit II Unit III
Naucalpan MRRA
AIBJ
Downtown Airport

UPEC MOCS MPAA
Cuajimalpa
Nezahualcóyotl

Unit I
Unit II
UIGF Unit I

0 4 8 0 4 8 0 4 8
2 6 10 km
0 2 6 10 km 2 6 10 km
19°35′
99°15′ W 99°00′

Figure 2. Left: Study area shaded digital elevation model with geotechnical subsoil classiﬁcation (white lines; GODF, 2004). Red and yellow
lines show the leveling transects described in the text and Figure 5. Global positioning system (GPS) sites referenced in the text are shown as
blue triangles. Center: Interferometric synthetic aperture radar (InSAR) fringe maps of Mexico City metropolitan area for 1 February to 16
May 1996. Right: InSAR fringe maps of Mexico City metropolitan area for 16 July 1999 to 7 January 2000. Each color cycle phase represents
28 mm distance change between sensor and ground. The digital elevation and fringe images have been merged and registered with a high-
resolution ASTER band 2 image.

1558 Geological Society of America Bulletin, November/December 2008


0.05 sides at an average annual rate of 115 mm/year,
while the current GPS rate is −84 mm/yr. These
0 rates are less than the historical maximum at this
Elevation change (m)

location (Fig. 4), consistent with the capping of
UIGF wells in the 1950s.
-0.05 Figure 4 shows a multitechnique compos-
ite plot of historical subsidence in the down-
-0.1 town area. Pre-1985 leveling data (Mazari and
InSAR Jul 1999–Mar 2000 (175 days) AIBJ Alberro, 1991) were collected at selected city
InSAR Feb–Mar 1996 (105 days) landmarks. The 1985–2002 data were derived
-0.15 GPS sites Jul 1999–May 2000 from leveling of a modern benchmark network
GPS sites Feb–May 1996 encompassing most of the city, surveyed at
-0.2 ~2 yr intervals by the former Dirección General
0 5 10 15 20 de Construcción y Operación Hidráulica (1993;
Distance (km) now Sistema de Aguas de la Ciudad de Mexico).
Although benchmarks used in Figure 4 are not
Figure 3. Elevation change versus distance (profile UIGF to AIBJ, see Fig. 2 for the same on the pre-1985 and post-1985 surveys,
location) for global positioning system (GPS) (triangles) and interferometric the closest modern benchmark to the location of
synthetic aperture radar (InSAR) (lines) for time periods of 1996 and 1999–2000 the historical landmarks was selected, typically
SAR interferograms. GPS displacement was calculated assuming constant rate within just a few hundred meters distance. Con-
for period 1995–2001, interpolated to time span of interferogram. The 1996 tinuous GPS data (2004–2007) from the current
interferogram is unadjusted for orbit error; the 1999–2000 interferogram shown permanent network (map on Fig. 2) are also dis-
is adjusted to match GPS data at UIGF near the southwest edge of basin. played in Figure 4.
Total subsidence of the downtown area
(Alameda park) between the end of the nine-
a mix of vertical and horizontal motion? A SAR estimate at AIBJ is 100 mm over 105 d (1996) teenth century, when artesian flow from the
interferogram from one look direction, as in our and 148 mm over 175 d (1999–2000), equivalent local water springs ceased, and spanning the
case, measures only the scalar length change in to average annual rates of 347 mm/yr (1996) and interval between the times first water wells
the satellite line of site direction and does not 309 mm/yr (2000), compared to the 291 mm/yr were drilled in the basin and present time is
resolve the three orthogonal components of the derived from the GPS campaigns. shown in Figure 4. Between 1895 and 2002, a
displacement vector. Also, the imaged changes The agreement between the different data total of 9.7 m subsidence occurred. The rates
may include short-term (e.g., seasonal) changes, sets with different time spans suggests several of subsidence since 1985 show sharp differ-
or could reflect longer-term trends. The avail- important points: ences with other areas east of downtown. Sub-
able SAR data do not address the issue of high- (1) Most of the InSAR recorded ground sidence rates of ~−57 mm/yr (1960–1985) and
resolution temporal variability. motion is vertical. Independent analysis of the −112 mm/yr (1985–1992) are comparable with
We recorded negligible GPS vertical veloc- horizontal component GPS data at MRRA, the current rate of −84 mm/yr measured by
ity at UIGF, outside the subsidence affected MPAA, UPEC, and MOCS confirms that hori- GPS techniques at UPEC.
zone, and high and constant subsidence at zontal motion at these sites is small. Subsidence rates of other eastern sites such as
AIBJ, at an average rate of −291 mm/yr for the (2) Short-term subsidence rates measured by Airport SW (benchmark M[S01E03]05), which
1995–2001 period using campaign data. More SAR in 1996 and 1999–2000 are similar to the lies close to GPS site AIBJ, show similar rates to
recently installed GPS sites at MOCS, MPAA, average rate for the period 1995–2001, the time the GPS-derived rates of subsidence: −215 mm/
and MRRA (Fig. 4) located on the high-sub- span of campaign GPS measurements at AIBJ. yr at Airport SW (leveling) compared to −211
sidence region show rates that range from −168 (3) It confirms that extraordinarily high rates mm/yr, −255 mm/yr, and −287 mm/yr for the
to −255 mm/yr and display linear trends with of surface subsidence are occurring within the GPS sites MPAA, MRRA, and AIBJ, respec-
no or very little annual variation. On the other Mexico City metropolitan area. tively. The daily sampled GPS data, and general
hand, the UPEC site, located further to the west The general agreement of the various subsid- agreement with rates derived from less frequent
(Fig. 4) where lacustrine sediments are thinner, ence estimates for different time intervals and leveling data, suggest essentially constant sub-
shows a lower subsidence rate (−84 mm/yr) but independent techniques (Fig. 4) indicates that sidence with little seasonal fluctuations.
displays small seasonal variations. the short-term SAR-based measured subsidence We also compared several techniques to
Figure 3 plots InSAR displacement, assuming process does not have a significant seasonal better characterize the post-1985 subsidence
only vertical motion, and the vertical component bias. The eastern part of Mexico City has been period. We used space geodetic data and com-
of GPS displacement for a transect across the subsiding at a fast and essentially constant rate pared them to the two main north-south leveling
basin that intersects UIGF and AIBJ GPS sites, for at least the past 10 yr. While short-term GPS- transects that run across the city (red and yel-
assuming that the longer-term average veloc- based rates (better shown on UPEC site; Fig. 4) low lines in Fig. 2). These are tied to reference
ity at the GPS sites (representing data spanning indicate fluctuations spanning a few week’s benchmarks on rock outcrops and are assumed
more than 6 yr at AIBJ) is representative of the period, these short-term fluctuations are small to be devoid of regional subsidence effects. A
average velocity over the 175 d (1999–2000) or compared to the long-term signal and probably temporal comparison of these leveling transects
105 d (1996) InSAR period. The three subsi- account for the small discrepancies between the (Fig. 5, top panels) indicates that except for a
dence estimates at AIBJ (two InSAR, one GPS) InSAR and GPS based estimates. For example, few benchmarks that exhibit anomalous behav-
agree fairly well. The InSAR-based subsidence InSAR data indicate that the old city center sub- ior, the rate remains essentially constant over


Cabral-Cano et al.

Mexico City Historical Subsidence GPS Vertical component
0 -100
Cathedral
-2 Palacio Minería -300

(mm)
Carlos IV
Relative subsidence (m)

-4 Monument -500
Downtown MRRA site rate: -255.8+/- 4.6 mm/yr

(M[S01E01]01) 0
2005 2006 2007

-6
Alameda Park
−200

-8 0

(mm)
−400
Airport NE (AIBJ)
-10 -2 −600 MPAA site rate: −211.8+/− 2.1 mm/yr
2005 2006 2007 2008
Airport SW (M[S01E03]05)
-12 -4 0

−100
-14 -6 (m)

(mm)
1900 1920 1940 1960 1980 2000 −200

Years UPEC site rate: −84.1+/− 6.2 mm/yr
r

2004 2005 2006 2007 2008
0

19°26′15″ N −100
Alameda UPEC
✪ ✪ ✪
✪
−200
(mm)
Carlos IV
P. Minería
✪ −300
Catedral −400 MOCS site rate: −168.6+/− 2.6 mm/yr
M[S01E01]01 2005 2006 2007 2008

✪
0 1 km
N 19°25′18″
99°09′08″ W 99°07′30″
Figure 4. Left: Multitechnique composite plot of the subsidence in the Mexico City downtown area since 1895. Pre-1985 leveling data were
collected at selected city landmarks, whereas 1985–2002 data were derived from leveling of a modern benchmark network. See text for further
explanation. Right: Vertical component time series for global positioning system (GPS) sites (red triangles) within the high subsidence region;
see Figure 2 for their location. Map inset shows location of leveling benchmarks (blue circles) and GPS site UPEC (red circle).

time. We then constructed a relative subsidence metric pair. The continuous GPS data give daily (3) Correspondence between the leveling and
plot following the same locations of benchmark measurements. Most of the continuous GPS InSAR rates is better displayed on the eastern
transects using InSAR-derived subsidence mag- sites show more or less continuous subsidence transect (Fig. 5, right middle and bottom pan-
nitude maps (Fig. 5, bottom panels). The most at an essentially constant rate; hence, the InSAR els) than on the western transect (Fig. 5, left
relevant observations from this comparison are and GPS rates may be usefully compared, even middle and bottom panels). This is evidenced
as follows: if they were acquired at different times. The by the overall correspondence in magnitude and
(1) InSAR-based relative subsidence transects conventional leveling transects are carried out location of high and low values of both eastern
show ~8× better spatial resolution compared to every 2 yr over a 2–4 wk period during normal leveling and InSAR plots (Fig. 5, right middle
leveling, and they are capable of resolving ver- working hours; the methodology includes a ref- and bottom panels). This may be a consequence
tical motion for areas less than 100 × 100 m, erence benchmark of known (static?) elevation of the magnitude of the subsidence rate, which
well within average city block dimensions in a and assumes a static reference frame during the is higher on the western transect, and is located
medium to high population density zone. period of the survey. Therefore, any leveling sur- mostly over lacustrine clays (Unit III on Fig. 2),
(2) Each technique has a characteristic time vey that is performed over high subsidence rate than on the eastern transect, located along the
interval that needs to be considered in the inter- areas, such as the eastern part of Mexico City, transitional zone (Unit II on Fig. 2).
pretation, especially if subsidence has a time- with rates over 250 mm/yr, may be biased by up Current maximum subsidence for the Mex-
varying rate, e.g., seasonal ﬂuctuations. The to ~9.5 mm in a typical 3 wk survey (differential ico City metropolitan area (Figs. 6 and 7) is
InSAR-derived transects represent an integrated subsidence between benchmarks at beginning localized at Ciudad Nezahualcóyotl (on the
measurement over the time span of the interfero- and end of survey). eastern side of the Mexico City metropolitan



Subsidence Rate Western Transect Subsidence Rate Eastern Transect
500 100

0
300
-100

(mm/yr)
(mm/yr)

Rate 1998–2000
100 Rate 1998–2000 Rate 2000–2002
0 Rate 2000–2002 Rate 1998–2002
Rate 1998–2002 -300
-100

-300
-500
0 10.0 20.0 30.0
-500
Benchmark Distance (km)

Subsidence Rate Western Transect (1998–2002) Subsidence Rate Eastern Transect (1998–2002)

20 50

0
(mm/yr)

(mm/yr)
0 -50

-40 -150

-80 -250
Benchmark Benchmark

Susidence Rate InSAR Western Transect Subsidence Rate InSAR Eastern Transect
150
Subsidence rate (mm/yr)

Subsidence rate (mm/yr)

50

50 0

0 -50

-50

-150

-150
Pixel Number
-250
Pixel Number
Figure 5. Comparison of two north-south–trending leveling transects (top and middle panels) and the corresponding interferometric synthetic
aperture radar (InSAR)–derived relative subsidence (bottom panels) along the same transects (location shown in Fig. 2). InSAR-based relative
subsidence transects show ~8× better spatial resolution compared to leveling. Subsidence rate magnitude is higher on the western transect,
which is located mostly over lacustrine clays (Unit III on Fig. 2), than on the eastern transect, which is over coarser-grain alluvial-fan deposits
(Unit II on Fig. 2). See text for further details.

area), southeast of the historical maximum sub- where current subsidence rates exceed a few tlán, and the lake was drained to build the new
sidence area. This area registered an average mm/yr corresponds closely to the lacustrine city, irrevocably changing the ecosystem and
annual rate of 378 mm/yr, close to the highest unit (Unit III on Fig. 2). In contrast, the western hydrologic balance.
annual subsidence rate in the downtown area part of the city, mostly built over alluvial-fan Further evidence supporting the strong cor-
recorded in the mid-twentieth century (~400 deposits and/or volcanic tephra, tuffs, and lava relation between subsidence and thickness of
mm/yr; see Fig. 4). This shift is important and ﬂows (Unit I), shows negligible motion. The clay-rich units is shown in Figure 8, where
suggests that water extraction has not declined, high subsidence region corresponds closely to we superimpose the seismically derived depth
but rather moved eastward. Compaction may the boundary of old Lake Texcoco just prior to of the Quaternary lacustrine clay unit (Perez-
now be affecting deeper units near the center Spanish settlement, when a major change in Cruz, 1988) and the subsidence magnitude
of the basin. agricultural practices and hydraulic manage- estimated for 2000. This clay unit is thickest in
Groundwater overdraft in the Iztapalapa- ment was initiated. The outer InSAR fringe in the high subsidence region east of the Mexico
Nezahualcóyotl region is acute; there has been Figure 2 (2000 data panel) maps the location City metropolitan area. This unit is 350 m thick
a sustained static piezometric level drop of of the lake boundary at the time of Spanish in the Texcoco-1 deep well (Fig. 8) and can be
−1.4 m/yr averaged over the past 20 yr (Lesser conquest of the Aztec empire, when Mexico seismically correlated under most of the Ciu-
y Asociados, 2003; Ortega, 1999). The region City was built over the ruins of old Tenochti- dad Nezahualcóyotl neighborhood.


Cabral-Cano et al.

1996 2000 2003

N N N

0 4 8 0 4 8 0 4 8
2 6 10 km 19°15′ 2 6 10 km 2 6 10 km
99°15′ W 99°00′
0 Subsidence rate -400 mm/yr

Figure 6. Examples of annual interferometric synthetic aperture radar (InSAR)–derived subsidence maps for Mexico City for 1996, 2000,
and 2003. White line shows the Distrito Federal political boundary.

2263 19°26′45″ N
2038 2624
AIBJ
1978 2380 N mm/yr
160
1903
-374
1258 514 Airport
1911 2666

689 165 1439
2
380
27
196 28
190 Ciudad Nezahualcoyotl
2681
Viaducto 44 38 942
14 45
13 2106 -187
rubusco

1757 Ca
2679 2221 lza
199
160 da
105 Za
128 rag
Tlalpan

267 oz
Rio Chu

1078 7 8 4 a
6 9
170 107
5
193 TEC-2 110
138
198
Div.

185
2259 162 2239 150 0
del N

53 243
119 244
192 50 151 123-126 0 2 4
1857 164 59
orte

167 152
2075 61
2161 2294 1 3 5 km 19°21′20″
99°09′45″ W 99°00′30″

Figure 7. Location of pilot wells used in the analytical subsidence calculation superimposed onto the 2003 interferometric syn-
thetic aperture radar (InSAR) subsidence map. Major streets are show as white lines.



19°30′07″ N
9
14

0
24
149
Texcoco

342
Figure 8. Seismically derived depth
Roma (black contours) of the Quaternary
lacustrine clay unit from Perez-
Cruz (1988) superimposed onto the
Mixhuca interferometric synthetic aperture
radar (InSAR)–measured subsid-
ence magnitude for 2000. Stars show
location of PEMEX deep wells.
240
149

149
14

Copilco 24
9

0
342 Deep stratigraphic borehole
Seismic depth contour (m)
Municipal boundary
24

Tulyehualco
0

454 34
0 2 4 2
0 Subsidence rate -400 mm/yr

1 3 5 km

19°14′00″
99°11′51″ W 98°59′00″

SUBSIDENCE GRADIENT (3) the Zaragoza corridor, which has a These areas are known for extensive damage to
NW-SE feature running parallel to this major housing and large civil engineering structures
We computed the horizontal gradients of avenue between the Agricola Oriental and Aca- such as subways and large hydraulic infrastruc-
subsidence rate from the subsidence maps to titla neighborhoods, including the Peñón del ture. Detailed information on the location and
investigate possible correlation with damage to Marqués area, on the eastern part of the Mexico extent of these zones from the InSAR-derived
infrastructure. Figure 9 shows the magnitude of City metropolitan area; and gradient maps provides a new and valuable tool
maximum horizontal gradient, computed from (4) a NE-SW corridor located immediately to to include in urban land use and mitigation of
the October–December 2003 ENVISAT-ASAR the SE of Canal de Garay Avenue and into the subsidence hazard.
image pair. While there are minor differences Santa Cruz Meyehualco neighborhood, north of
between gradients computed from the various Calzada Ermita Iztapalapa. ANALYSIS OF SUBSIDENCE DATA
interferograms, all show four regions of large All of these regions coincide with Quaternary
horizontal subsidence gradient: volcanic features in close proximity to lacus- The consolidation analysis (Terzaghi and
(1) southern slopes of the Sierra de Guadal- trine clay-rich sediments. These high-gradient Peck, 1967) establishes a relationship between
upe, north of Mexico City; zones mark the location of abrupt transitions those changes in effective stress caused by
(2) Peñón de Los Baños, immediately north between continuous subsidence of the lacus- extraction pumping in an aquifer and the result-
of Mexico City International Airport; trine beds and stable volcanic outcrops (Fig. 2). ing deformation of its porous matrix, as follows:


Cabral-Cano et al.

19°30′00″ N

N

0.04

0.0
0 4 8

2 6 10 km 19°14′00″

19°17′00″ W 99°00′00″
Figure 9. Horizontal subsidence gradient for the Mexico City metropolitan area calculated from the 2003 subsidence magnitude
map. High gradient (nondimensional) values depict areas where structural damage risk to housing and other civil engineering
structures is higher due to intense surface fracture and faulting. These areas coincide with transitional piedmont zones between
Cenozoic volcanic structures and clay-rich Quaternary lacustrine deposits.

dV
= α γ dh , (1) head, this equation can be rewritten in terms of subsidence values following Equation 2 at those
V the land subsidence (b0 – b), where b0 and h0 are water-well locations shown in Figure 7, using
the reference (datum) conditions, i.e., b(h0) = b0. compressibility (α) values that correspond to
where V is the aquifer porous matrix bulk vol- This equation assumes that the surface responds clay, silt, and sand soils (Freeze and Cherry,
ume, α is the porous media compressibility, γ is instantly to changes in piezometric head. 1979). We used a value for the speciﬁc weight
the speciﬁc weight of water, and h is the piezo- of water of γ = 9800 N/m3 and a reference aqui-
b0 − b
metric head (groundwater table elevation) in = 1 − exp [ − α γ (h0 − h) ]. (2) fer thickness of b0 = 80 m (Ortega et al., 1993).
the aquifer. Assuming that deformation of the b0 This analysis suggests that the land subsidence
porous matrix occurs predominantly in the verti- observed in the vicinity of these wells can be
cal direction and solving for the thickness of the Figure 10 compares the InSAR-measured represented with soil parameters that correspond
aquifer as a function of the change in piezometric subsidence values to those analytically derived to a spatial composite of silt and clay. The offset



0.2 Active Archive Center (EDC-DAAC). We thank
Francisco Correa-Mora, Gerardo Cifuentes-Nava,
α = 10–6 Pa–1 (clay) Esteban Hernández-Quintero, Teodoro Hernandez-
α = 10–7 Pa–1 (silt)
Treviño, and Mario Mártinez-Yáñez for field sup-
Analytical subsidence (m)

0.15 port, and F. Amelung, D. Galloway, T. Holzer, D.
α = 10–8 Pa–1 (sand) Eaton, and other anonymous reviewers for their com-
ments, which improved this paper. This paper is pub-
lication 12 from the Center for Southeastern Tropical
0.1
Advanced Remote Sensing (CSTARS).

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ACKNOWLEDGMENTS
essentially constant subsidence rate, implies that fondo de la Ciudad de México ha producido el drenaje
subsidence is due mainly to pressure loss in the de las aguas del subsuelo, por las obras del desague
This work was funded by the Office of Naval
y rectificación de los errores a que ha dado lugar una
shallow aquitard (clay-rich lake sediments) asso- Research (ONR), the National Aeronautics and incorrecta interpretación de los efectos producidos:
ciated with groundwater overdraft (withdrawal in Space Administration (NASA), Universidad Nacio- Revista Mexicana de Ingeniería y Arquitectura, v. III,
excess of recharge). This poses important impli- nal Autónoma de Mexico (UNAM) Projects Papiit p. 96–132.
IN-121515 and IN-114907, and Geofisica-Cardi. Ghiglia, D.C., and Pritt, M.C., 1998, Two Dimensional Phase
cations for water management in the Mexico European Remote Sensing satellites (ERS)-1, 2, and Unwrapping: New York, John Wiley and Sons, 103 p.
City metropolitan area because compaction of Envisat data were provided by the European Space Gobierno del Distrito Federal, 2004, Normas técnicas
Agency (ESA) Projects AO-3 441 and CAT-1 1409. complementarias para diseño y construcción de cimen-
clay-rich aquitards is often associated with per- taciones: Gaceta Oficial del Distrito Federal, v. II,
manent loss of porosity and reservoir capacity NASA’s Earth Observing System provided Advanced
103-BIS, p. 11–39.
Spaceborne Thermal Emission and Reflection Radi- Goldstein, R.M., Zebker, H.A., and Werner, C.L., 1988,
(Holzer, 1984). Our data suggest that mitigation ometer (ASTER) imagery through the Unites States Satellite radar interferometry: Two dimensional phase
activities have not had a significant effect on the Geological Survey Earth Resources Observation and unwrapping: Radio Science, v. 23, p. 713, doi: 10.1029/
long-term compaction of the lacustrine beds. Our Science Data Center Land Processes Distributed RS023i004p00713.


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MANUSCRIPT RECEIVED 9 MARCH 2006
Los Problemas de la Cuenca de México: Mexico City, sidence due to Ground-Water Withdrawal: UNESCO
REVISED MANUSCRIPT RECEIVED 22 OCTOBER 2007
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