Reconnaissance of the 2017 Central Mexico Earthquake

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Reconnaissance of the 2017 Central Mexico Earthquake
Yolanda ALBERTO1, Hiroyuki KYOKAWA2, Masahide OTSUBO3, Takashi
KIYOTA4 and Ikuo TOWHATA5
1Member of JSCE, Assistant Professor, GWP, Graduate School of Engineering, University of Tokyo
(7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan)
E-mail: h-yolanda@t-adm.t.u-tokyo.ac.jp
2 Member of JSCE, Assistant Professor, Dept. of Civil Eng., University of Tokyo
(7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan)
E-mail: kyokawa@civil.t.u-tokyo.ac.jp
3 Member of JSCE, Research Associate, Inst. Industrial Science, University of Tokyo
(4-6-1 Komaba, Meguro-ku, Tokyo 153-8505. Japan)
E-mail: otsubo@iis.u-tokyo.ac.jp
4Member of JSCE, Associate Professor, Inst. Industrial Science, University of Tokyo
(4-6-1 Komaba, Meguro-ku, Tokyo 153-8505. Japan)
E-mail: kiyota@iis.u-tokyo.ac.jp
5Fellow of JSCE, Visiting Professor, Dept. of Civil Eng., Kanto Gakuin University
(1-50-1 Mutsu-ura-Higashi, Kanazawa-Ku, Yokohama 236-8501, Japan)
E-mail: towhata.ikuo.ikuo@gmail.com
Key Facts
・Hazard Type: Earthquake
・Date of the disaster: September 19th, 2017
・Location of the survey: Mexico City, Puebla, Morelos
・Date of the field survey: October 15th to 19th, 2017
・Survey tools: Microtremor
・Key findings: site effects, contribution of sinking to the amplification of damage, need for imple-
mentation of mandatory retrofitting of old structures and seismic revision of damaged structures
Key Words: site reconnaissance, building damage, ground failure, Mexico Earthquake, Puebla Earth-
quake
1. INTRODUCTION
On September 19, 2017, 13:14 local time, an intra-
plate earthquake (Mw=7.1) was registered at the state
limit of Puebla and Morelos, in the central part of
Mexico. The epicenter (18.40N and 98.72W) was lo-
cated 120 km away from Mexico City and 90 km
away from Puebla City, at a depth of 57 km (Fig. 1).
The maximum peak ground acceleration registered
by the Institute of Engineering of the National Auton-
omous University of Mexico, was 170 cm/s2, 109 km
away from the epicenter1). The earthquake caused
369 casualties and affected Mexico City and the
states of Puebla, Morelos, Guerrero, Hidalgo, Tlax-
cala and State of Mexico2). In Mexico City, 2273
houses had total damage and 3492 partial damage3).
This earthquake occurred exactly 32 years after the
1985 Michoacan Earthquake that hit the Pacific
Coast of Mexico City and caused at least 40,000 cas-
ualties and around 3.5 billion dollars in damage.
A brief reconnaissance was carried out from Octo-
ber 15th to 19th, 2017 with the main focus of observing
building and geotechnical damage. A map of the sites
visited is displayed in Figures 1 and 2. The areas of
interest were the districts of Centro, Condesa, Roma,
and Villa Coapa, and the counties of Xochimilco and
Tlahuac in Mexico City; Tlayacapan and Cuernavaca
in the state of Morelos; and Puebla City in the state
of Puebla. This paper will introduce a brief back-
ground on the geological and soil conditions of Mex-
ico City, to understand the extent of damage during
this seismic event. The results of a series of micro-
tremor measurements on key areas, are presented to
illustrate the ground motion vibration characteristics.
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The affected sites observed during the visit will be
discussed. Whenever relevant, pictures of the previ- ous condition will be compared with the damage en-
countered.
Fig. 1 Location of the epicenter and the sites visited
Fig. 2 Location of the seismic stations and points of microtremor tests in Mexico City
2. GEOLOGICAL SETTING OF MEXICO
CITY
Mexico City is located on the subduction region of
the Cocos and the North American Plates. The Basin
of Mexico, that comprises Mexico City and a part of
the State of Mexico, started as a subduction zone at
5 km
100 km
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the beginning of the Miocene, then turned into a val-
ley when the volcanic activity blocked the west and
east sides, and finally, became a lacustrine basin at
the end of the Pleistocene, when it was surrounded by
mountain ranges that stopped the drainage of the ba-
sin. Lakes started forming in the depressions during
the rainy seasons and evaporated during the droughts,
which originated the accumulation of sand, silt, clay,
ash and alluvial clastic deposits. When the first hu-
man settlements started, there were five lakes:
Zumpango, Xaltocan, Texcoco, Xochimilco and
Chalco4). Eventually, these lakes dried out as urban
settlements grew.
As a result of the climate changes and volcanic ac-
tivity, the Basin of Mexico is composed of volcanic
rocks and lacustrine sediments. The central part of the
basin is filled with sandy silt, clayey silt and interbed-
ded layers of volcanic ash or sand. In the high zones,
there are basalt deposits and the Tarango formation
formed by calcium carbonate-cemented sand, silt and
gravel5) (Figure 3).
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
0
10
20
30
40
50
60
70
80
90
100
110
TRANSITION LAKE
Upper clay formation
Black sand
Crust
Volcanic ash
Lower clay formation
Hard layer
Hard layer
Deep clay formation
Volcanic glass
Tarango
Deep alluvial deposits
Basalt
formation
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
0
10
20
30
40
50
60
70
80
90
100
110
Latin-American
Cathedral
TRANSITION
International
Reforma
Zaragoza
LAKE
Tower
Fill
Upper clay formation
Black sand
Crust
Volcanic ash
Lower clay formation
Hard layer
Hard layer
Deep clay formation
Volcanic glass
Tarango
Deep alluvial deposits
Basalt
formation
Airport
Fig.3 Soil profile in Mexico City6) (East-West cross section)
2.1 Seismic zoning
Due to the soil characteristics and seismicity, Mex-
ico City was divided into three general zones by Mar-
sal and Mazari5): zone I (Hill), zone II (Transition)
and zone III (Lake). After the 1985 Michoacan Earth-
quake, the Building Code of Mexico City included
went further to divide zone III (lake) into four differ-
ent areas according to the variations observed in fun-
damental period and maximum spectral acceleration.
Zone I, also known as Hill, is formed by rocks and
stiff soil with small interbedded layers of loose sand
or clay.
Zone II, called Transition, is formed by sandy and
silty layers, and the bedrock is usually located at 20
m depth. The seismic response of this zone shares
characteristics of both Zone I and Zone III.
Zone III, also known as the Lake zone, is formed
by soft soil deposits with interbedded layers of sand
or silt. It is located in the central part of the Basin of
Mexico, where the main lakes used to be, and in these
areas, the bedrock is located at 30 to 50 m depth.
At the west side of the city, the transition between
zones is abrupt (Figure 4). During this earthquake,
the damage concentrated in zones II and III, in the
southwest part.
Figure 5 depicts the design spectra established by
the Building Code of Mexico City for each zone.
Fig.4 Seismic zonation of Mexico City7)
Fig.5 Design spectra for each zone7)
3. STRONG GROUND MOTION RECORD
AND MICROTREMOR MEASUREMENT
Figures 6 to 8 show the seismic records obtained
from the National Seismological Service, in three
seismic zones and depicted as acceleration time his-
tories in Figure 2. The frequency components are also
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shown at the bottom of each figure, where the pre-
dominant frequency can be clearly appreciated. The
acceleration time histories display the different char-
acteristics of the three different stratigraphies. The
maximum accelerations in each zone and direction
are summarized in Table 1.
The predominant period increases from zone I to
zone III. In zone III the predominant period ranges
from 1.7 to 2 s, while in zone II the predominant pe-
riod ranges from 0.7 to 1.1. The peak ground acceler-
ation in zone III exceeds 100 cm/s2 which is lower
than the peak ground acceleration (PGA) in that area,
160 cm/s2, during the 1985 Michoacan Earthquake.
However, PGA in zone I was around 30 cm/s2 in
19858), which means that the value during the Central
Mexico Earthquake was twice as big.
Nakamura and Sato9) reported that the use of mi-
crotremor can be very effective to properly character-
ize the earthquake response of ground and structures.
Therefore, microtremor measurements were done in
spots representative of the three seismic zones, as de-
picted in Figure 2. Three components of ground mo-
tion (x, y, z) were recorded for 180 s using a micro-
tremor, and three measurements were conducted at
each location. Fast Fourier transform was applied to
the data sets, and the three measurements were con-
sidered to smooth the frequency domain responses in
the three components (sx, sy and sz).
The H/V ratio was calculated as  
=

.
.
The H/V ratio increases and the dominant fre-
quency decreases from zone I to zone III (Figure 9).
This is consistent with the results from Singh et al.8)
During the 1985 Michoacan Earthquake, the am-
plitude of the seismic waves with oscillation periods
greater than 2 s was around 10 times bigger, while the
amplitude of seismic waves during the Central Mex-
ico Earthquake for oscillation periods less than 2 s,
was 5 times bigger1). This had direct impacts on the
damage to buildings.
Fig.6 Acceleration time history in Zone 110)
Fig.7 Acceleration time history in Zone II10)
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Fig.8 Acceleration time history in Zone III10)
Table 1. PGAs at three seismic zones
Zone
Peak ground acceleration (Gal)
N00E/S00E
N90W
V
I (Hill)
74.69
79.26
35.51
II (Transition)
70.49
83.91
28.19
III (Lake)
111.99
98.03
36.39
Fig.9 H/V spectrum ratio of Zones I, II and III
4. BUILDING DAMAGE
During the September 19, 2017 Central Mexico
Earthquake, building damage concentrated in the
central and south parts of Mexico City, especially in
zones II (Transition) and IIIa (Lake). Officially, 46
buildings collapsed and a total of 5765 buildings had
some level of damage3). Buildings with 5 to 10 stories
suffered from moderate to severe damage11). In Fig-
ure 10 the buildings collapsed in 2017 (red points) are
overlapped on the seismic zonation, Zone II repre-
sented by the blue area and Zone III by the red area.
Blue points are the collapsed buildings during the
1985 Earthquake, displayed for comparison. In the
following sections, some representative examples
will be described.
Fig. 10 Collapsed buildings of 2017 (red points) and 1985 (blue points)
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4.1 Damage observed
The visit began at the districts of Centro, La Con-
desa and Roma Norte, that are distinguished for hav-
ing thick clay layers and were severely affected dur-
ing the 1985 earthquake, when around 760 buildings
collapsed. The map of the studied sites is shown in
Fig. 2.
Then, the districts of Coyoacan, Tlalpan and Villa
Coapa, were visited to observe structural damage in
the south part. In 1985, the damage concentrated in
the central part, while the southern part did not ex-
hibit significant losses. In overall, it was observed
that buildings that collapsed in 1985 had longer nat-
ural periods than those that collapsed this time. Bray
et al.,12) proposed a damage index of structures that
was used to classify the observed buildings (Table 2).
Table 3 is a summary of the buildings surveyed,
their damage index and observations.
Table 2. Damage index of structures
Index
Description
Interpretation
D0
No observable
damage
No cracking, broken glass,
etc.
D1 Light damage
Cosmetic cracking, no ob-
servable distress to load-
bearing structural ele-
ments
D2 Moderate damage
Cracking in load-bearing
elements, but no signifi-
cant displacements across
these cracks
D3 Heavy damage
Cracking in load-bearing
elements with significant
deformations across the
cracks
D4 Partial collapse
Collapse of a portion of
the building in plan view
(i.e., a corner or a wing of
the building)
D5 Collapse
Collapse of the complete
structure or loss of a floor
4.1.1 Centro
In the central district, one of the most distinguished
structures was the Latin-American Tower, a 44-story
building finished in 1956 (Figure 11). Its foundation
consists of a combination of point bearing piles to a
depth of 33 m and a reinforced concrete box at a
depth of 13.5 m. The Latin-American Tower has sur-
vived the earthquakes of 1957 and 1985. During this
earthquake, no damage was observed in the structure
(D0).
Figure 12 shows the buildings near the Latin-
American Tower which exhibited 1° of tilting. Alt-
hough a previous picture (Figure 12 right) shows that
these buildings have tilted before, the base of the
building shows recent differential settlement (Figure
13).
Table 3. Buildings surveyed
Location
No.
in
Fig.
10
Damage
index Zone and com-
ments
Latin-Amer-
ican Tower,
Centro
1
D0 Zone III, steel
frame
La
Nacional,
Centro
2
D2
Zone III, RC struc-
ture, corner build-
ing
Puebla 282,
Roma Norte
3
D5
Zone II, 4-story,
masonry and con-
crete, soft-story
building
Alvaro
Obregon
286, Roma
Norte
4
D5 Zone II, 7-story,
RC structure
Puebla St.
and Cozu-
mel St.,
Roma Norte
5
D2 Zone II, 11-story,
RC structure, cor-
ner building
Cozumel
52, Roma
Norte
6
D2
Zone II, 10-story,
masonry and con-
crete, corner and
soft-story building
Amsterdan
15, Condesa
7
D5
Zone II, 9-story,
RC structure, cor-
ner and soft-story
building
Amsterdan
St., Condesa
8
D2
Zone II, 8-story,
RC structure, cor-
ner building
Amsterdan
St. and
Cacahua-
milpa St.,
Condesa
9
D3
Zone II, 7-story,
RC structure, cor-
ner and soft-story
building
Avenida So-
nora 149,
Condesa
10
D5 Zone II, 8-story,
RC structure
Alvaro
Galvez and
Fuentes,
Coyoacan
11
D5 Zone III, 5-story,
RC structure, cor-
ner building
Elementary
School “En-
rique
Rebsamen”,
Villa Coapa
12
D5 Zone III, 4-story,
RC structure, cor-
ner building
Los Arcos,
Villa Coapa
15
D5
Zone III, 6-story,
RC structure, no
adjacent buildings
Miramontes,
Villa Coapa
16
D2
Zone III, 6-story,
RC structure, cor-
ner building
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Fig.11 Latin-American Tower, D0, Zone III
Fig.12 La Nacional and Sears, Centro District, D2, Zone III
Fig.13 Corner of La Nacional, Centro District, D2, Zone III
4.1.2 Roma Norte
In the district of Roma Norte, several buildings of
5 to 10 stories experienced moderate damage (D2) to
total collapse (D5) given that most of the structures
in the area were built before 1985.
Figure 14 shows a damage to 7-story reinforced
concrete structure (RC) building in Alvaro Obregon
286. It was surrounded by smaller buildings and col-
lapsed immediately after the earthquake, causing
damage to the buildings on the left and the back that
had to be evacuated. This issue, known as pounding,
was observed in many instances after this earthquake.
Fig.14 Alvaro Obregon 286, D5, Zone II
Figure 15 shows a 10-story building between Pue-
bla Street and Cozumel Street, exhibited peeling of
surface and collapse of a masonry concrete block.
Built before 1985, it underwent minor repair after
that earthquake but it was evacuated this time. Asym-
metric damage was observed due to the corner loca-
tion and the 2-story house on the right side.
Fig.15 Puebla and Cozumel Streets, D2, Zone II
4.1.3 La Condesa
In this area, there were several collapses, such as
the RC structure with masonry bricks in the corner of
Amsterdan and Laredo Streets (Figure 16). This 9-
October, 2017
May, 2015 (Google map)
October, 2017
January, 2017 (Google map)
October, 2017
March, 2016 (Google map)
October, 2017
March, 2016 (Google map)
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story building was located on the corner and had an
8-story building on the left side that suffered moder-
ate damage (D2).
Fig.16 Amsterdan 15, D5, Zone II
A particular case was the 8-story building shown
in Figure 17. This building in Avenida Sonora had
the collapse of the sixth floor. It was surrounded by
lower buildings on both sides. A repair mark was ob-
served on the side of the RC structure, which could
indicate previous repairs in the building. A reduction
in stiffness from the fifth floor to the sixth floor could
have caused the loss of the latter.
One of the main issues in the district of La
Condesa, along with Roma, Narvarte and Del Valle,
is that they suffered great damage after the 1985
Michoacan Earthquake and not all the buildings were
properly retrofitted.
Fig.17 Avenida Sonora 149, D5, Zone II
4.1.4 Tlalpan and Coyoacan
Tlalpan and Coyoacan are two counties in the
south of Mexico City that lay on the seismic zones II
and III.
A residential building in Coyoacan collapsed after
the shaking. The 5-story building was on a corner sur-
rounded by trees and only the ground floor remained
(Figure 18). The direction of this building was differ-
ent from the surrounding buildings in the block, that
were built at the same time, before the 1985 Micho-
acan Earthquake.
In the county of Tlalpan, several residential and
commercial buildings were damaged in the district of
Villa Coapa. One of the most relevant cases was the
elementary school “Enrique Rebsamen”, in which
one of the 4-story buildings collapsed completely
(Figure 19).
Fig.18 Residential building in Coyoacan, D5, Zone III
Fig.19 School “Enrique Rebsamen”, D5, Zone III
4.2 Overview of building damage
The collapsed buildings are displayed in Figure 20,
most of them lying on Zone II and Zone III. Table 3
presents a summary of the buildings observed and the
damage level.
The structural systems of damaged buildings sur-
veyed in Mexico City, were RC structures, masonry
October, 2017
March, 2016 (Google map)
October, 2017
March, 2016 (Google map)
October, 2017
January, 2017 (Google map)
October, 2017
February, 2017 (Google map)
CNN ( http://edition.cnn.com/2017/09/21/americas/mexico-
earthquake/index.html)
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and concrete and steel frames. Other relevant charac-
teristics were the location and the stiffness. Corner
buildings represented 41% of all the collapsed build-
ings, while soft-story buildings were 57%11).
Fig.20 Seismic zonation and buildings collapsed
One of the most important observations was that
most of the collapsed buildings were built before
1985 and were rehabilitated after minor repairs, for
residential or commercial purposes. After the 1985
Michoacan Earthquake, the seismic evaluation of
buildings that underwent minor damage was not
mandatory, which made these structures more vul-
nerable during this earthquake.
5. GROUND FAILURE
Mexico City has experienced continuous ground sub-
sidence since the last century. In 1890, the govern-
ment started extracting water for consumption from
deep wells located in the center of Mexico City. In
1925, the problem was acknowledged after measur-
ing the settlement of the Cathedral. In 1960, the water
extraction stopped in the central part but continued in
the south part, in the areas of Xochimilco, Tlahuac
and Iztapalapa. However, the subsidence has not
ceased in the central area and has also started in the
south of the city13) (Figures 21 and 22).
This extraction has caused differential settlements
and generation of cracks due to the desiccated soils,
that have affected buildings, roads and historical re-
mains. Particularly, the counties of Tlahuac and Xo-
chimilco, that are characterized for being located in
the old area of lakes and are the places where deep
wells are extracting water for Mexico City, showed
great damage due to ground failure14).
Fig.21 Subsidence in the center of Mexico City13)
Fig.22 Subsidence in the south of Mexico City13)
5.1 Colonia del Mar
In Colonia del Mar, a district located in the region of
Tlahuac, cracks have been reported since 1970. After
the earthquake, the Geosciences Center of the Na-
tional Autonomous University of Mexico (UNAM)
released an official map of cracks in Mexico City15)
to deal with the reconstruction in the counties of
Tlahuac, Xochimilco and Iztapalapa because during
the earthquake, the existing cracks increased their ex-
tension and depth.
Site 1, in Fig. 23, is a park on the border between
Tlahuac and Iztapalapa counties (Figure 24). In this
area, the local government had previously built a sub-
sidence monitoring station, that can be seen in the
back, because the park had been settled for a while.
However, a settlement of around 1 m was observed
on the running track immediately after the earth-
quake, and on the date of the survey, the maximum
settlement was 1.3 m.
Site 2 was a house located in Oceano St. and
Pingüino St., were the pavement displaced down-
wards in the transverse direction of the street (Figure
25). Inside the house, along the line of the outside
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crack, an existing sinkhole expanded. The sinkhole
opened the year earlier but the size significantly in-
creased after the earthquake (Figure 26).
A similar phenomenon was seen in Site 3 (Figure
27), nearby Marist University, where a sinkhole ex-
panded, exposing the pipelines under the street. The
cavities inside might indicate that a process of inter-
nal erosion have been taken place for a long time, just
as in other areas of Colonia del Mar.
Along the major cracks, most of the houses were
evacuated due to the risk of collapse. The houses,
built of masonry and concrete, exhibited cracks, sink-
holes and differential settlement. Although in this
area it is recommended to have 1-story houses due to
the cracks and geologic faults, several houses have
two or even three stories.
Fig.23 Area surveyed in Colonia del Mar
Civil Protection carried out a survey after the
earthquake and it was concluded that only in Colonia
del Mar, 216 properties had low risk of collapse, 477
had medium and 340 had high risk16). In Tlahuac, a
total of 1240 houses is in high risk, due to the
damaged caused by the earthquake and the existing
cracks.
Fig.24 Site 1. Settlement in a park
Fig.25 Site 2. House with a sinkhole
Fig.26 Site 2. Sinkhole inside of the house
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Fig.27 Sinkhole nearby Marist University
5.2 Xochimilco
In the area of Xochimilco, one lane of the Tulye-
hualco-Xochimilco roadway had to be closed due to
the appearance of longitudinal cracks and cavities of
even 1 m depth (Figure 28).
In this area of Xochimilco, houses are built on the
slopes of the hill and after the earthquake, the retain-
ing walls adjacent to the roadway leaned outwards
(Figure 29). Besides, there were water outages and
leakages in all the district; three weeks after the earth-
quake, the water service was not fully restored yet.
Fig.28 Damage in the Tulyehualco-Xochimilco highway
Transit was restricted to one lane; however, it was
learnt that in the working lane a sinkhole of about
0.7 m diameter and 5.3 m depth, opened six months
before the earthquake and was filled weeks later. This
indicates that this district, also part of the water ex-
tracting area, is prone to cracks and cavities.
Fig.29 Inclination of retaining walls
5.3 Morelos
In the district of Piedra Grande, Tlayacapan, Mo-
relos, the earthquake triggered a rock slide, that en-
dangered more than 20 houses on the hill (Figure 30).
The rock mass (60 m height and 25° slope) exhib-
ited fractures in the steeper areas. The fragments of
tuff on the foot of the hill ranged from 30 to 50 cm
diameter. Most of boulders (∼1.5 m diameter) that
slid were blocked by an older rock mass from a pre-
vious rockslide and just one hit a house in construc-
tion and perforated the wall as displayed in Figure 31.
As told by the neighbors, the site has been threatened
by the possible sliding of the rock mass for several
years, but just after the earthquake people was told to
evacuate
Fig.30 Rock mass in Tlayacapan, Morelos
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Fig.31 House wall destroyed by rock falling
5.3 Puebla City
Puebla City is located 90 km away from the epi-
center. The city has a population of about 6 million
and it has more than 2000 churches and temples. It
has a seismic setting due to its proximity to the Trans-
Mexican Volcanic Belt.
This time, the damage concentrated in the central
part and historical buildings, where 34 properties had
structural issues. There were cracks and cosmetic
damage in the dome of the tabernacle at the Cathedral
(Figure 32).
The church of San Juan de Letran had structural
damage and was closed. The structure of masonry
tilted and was supported by wooden beams (Figure
33).
Besides the historical and religious buildings, new
buildings experienced cosmetic damage and crack-
ing. Structures such as the High Towers in Lomas de
Angelopolis were built after the 1999 Tehuacan
Earthquake and exhibited damage in the roof and the
façade (Figure 34).
Fig.32 Cathedral in Puebla City
Fig.33 San Juan de Letrán, Puebla City
Fig.34 Plaza Sonata. Photo by Pilar García Téllez.
6. CONCLUSIONS
The September 19, 2017 Central Mexico Earth-
quake affected all the surrounding states but caused
significant damage in Mexico City, where the site
conditions and basin chracteristics amplified the
ground motion. Most of the structural damage con-
centrated in zones II and III where the previous 1985
Earthquake have also caused numerous collapses.
Due to the characteristics of the ground motion, 5 to
10-story buildings were the most affected in the west
side of Mexico City where the soft deposits have
thickness of 10 to 30 m (zone II and zone III). There
were significant factors shared by the collapsed
buildings, most of them were built before the 1985
Michoacan Earthquake, and they were corner and
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soft-story buildings. This pattern of damage is similar
to that experienced in 1985. It is expected that the
building code reinforces the need for seismic revi-
sions and retrofitting to all the structures that under-
went damage during this earthquake to prevent future
damges.
In the south part of Mexico City, the earthquake
worsened the existing problems. In both Tlahuac and
Xochimilco, the phenomenon of subsidence have af-
fected the ground generating cracks and sinkholes
which opened or expanded during this earthquake.
The recovery of this area will be very complex, as the
previous subsidence conditions and the problem of
water extraction need to be addressed, in addition to
the earthquake damage. Regarding other geotech-
nical issues, there was no liquefaction and few cases
of slope failure.
Other states of Mexico were also severely affected
and in some cases, it will be necessary to relocate
people to reduce the risk of future seismic events.
ACKNOWLEDGEMENT: The authors would
like to thank Prof. Gabriel Auvinet of the Na-
tional Autonomous University of Mexico for
providing important information regarding the
subsidence of Mexico City.
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