Transcript Effects of the 1985 Earthquake in Mexico City

September 19, 1985
7:19 am
The complete seismic event consisted of four quakes.
A pre-event quake of magnitude 5.2 occurred on
28 May 1985. The main and most powerful shock
occurred 19 September, followed by two aftershocks:
one on 20 September 1985 of magnitude 7.5 and the
fourth occurring seven months later on 30 April 1986
of magnitude 7.0.
An 8.1 magnitude earthquake
hits Mexico City, Mexico.

The earthquake shook the buildings in Mexico
City for a total of three horrifying minutes.
Thirty six hours later a 7.5
magnitude earthquake hits the
city again.
The epicenter was
later located 50 km
(approximately 31
miles) off the coast of
Mexico.
The Seismic Event
Magni
Date
tude
7.9
Jan. 9,
1857
7.9
April 18,
San Francisco
1906
7.8
7.5
7.3
7.3
7.3

Historic seismic activity in this
region causes Mexico to
experience about five times as
many major earthquakes as
California, with greater frequency
of recurrence.
Location
7.2
7.2
7.2
7.1
7.1
6.9
6.7
6.6
Fort Tejon
Comments
2 killed, 220-mile
surface scar
3,000 killed, $524 million
in property damage,
including fire damage
March 26,
27 killed, 3 aftershocks
Owens Valley
1872
of 6.25+
July 21,
12 killed, 3 aftershocks
Kern County
1952
of 6+
Jan. 31,
West of Eureka* 37 miles offshore
1922
Nov. 4,
No major injuries, slight
SW of Lompoc*
1927
damage
June 28,
1 killed, 400 injured, 6.5
Landers
1992
aftershock
Jan. 22,
Damaged homes in
Mendocino
1923
several towns
Nov. 8,
Injured 6, $1.75 million
West of Eureka*
1980
in damage
April 25, Cape
6.5 and 6.6 aftershocks
1992
Mendocino*
Oct. 16, Ludlow (Hector Remote, so minimal
1999
Mine Quake)
damage
May 18,
1940
Oct. 17,
1989
Jan. 17,
1994
Feb. 9,
1971
El Centro
9 killed, $6 million in
damage
Loma Prieta
63 killed
Northridge
San Fernando
61 killed, $15 billion in
damage
65 killed, $50 million in
damage

Because of the long duration of shaking, deep soil
deposits were excited resulting in amplified ground
movement.

Mexico City is built
partially on alluvial
lake deposits that
average from 100 –
150 feet thick.
Original Water Level
100-150’
Building Structures
Weak soil deposits


At some location of
Mexico City where most
of the damages are
found, soil deposits
extend to about 7500 ft
(2300 m).
Therefore, earthquake
vibrations in this areas
of Mexico city were
catastrophically
amplified.
Original Water Level
7500’
Building Structures
Weak soil deposits
Tectonics
This is a region where the Cocos Plate is being subducted underneath Mexico and is
the most active subduction thrust fault in the western hemisphere.


The Cocos Plate made one of its all too frequent
downward movements.
This time a 200 km long front, inclined 18
degrees east, thrust downward and eastward
about 2.3 m in two distinct jerks about 26 sec
apart.
Effects of the 1985
Earthquake in
Mexico City

Building
Structural
Damages:





Large number of the
collapsed buildings were
frame structures.
Large number of which
did not meet the
building standards.
Debris falling
onto parked cars
Liquefaction.
Loss of
Communication
Media.
Structural Damages
Bottom-level Failure Due to Weak First Floor
Collapsed School Building
School buildings are exposed to risk form earthquakes since they lack
adequate stiffening in shear walls of large classroom areas.
The amplitude of the shaking increases
up the building
Building with long axes perpendicular
to ground motion suffer more shaking
Building with different heights sway at
different frequencies and bank into each
other
A building with different height tend to
break apart
http://www.frame3d.caltech.edu/animations/b1tabxabsmov.gif
Collapsed Floors Punctured by Load-Bearing Column
Severe resonance oscillations of the buildings caused strain at the
juncture between columns and ceiling slabs. The vertical columns
were punched through the heavy floors that collapsed around
them.
Total Collapse of Juarez Hospital
Over four hundred medical personnel and patients were trapped in the
maternity wing of the Juarez Hospital. Survivors were still being
retrieved from the structure as late as ten days after the earthquake.
Collapsed 21-Story Office Building
Buildings such as the one standing in the background met building
code requirements. Obviously the collapsed office building did not.
Car Demolished by Debris
Thousand of vehicles were destroyed, like the one in this picture, by
falling debris.
Collapsed and Undamaged Office Buildings
The 44-floor Torre LatinoAmericana office building in
the background on the right,
remained almost totally
undamaged, as it did in a
1957 earthquake. The
building is a symmetrical
steel frame structure built to
resist earthquakes
High Rise Building
This building twisted excessively in
the earthquake, forming the Xshaped cracks.
The earthquake subjected the
building to shear, bending,
tensional forces, and compression.
The formation of the X-shaped
cracks is evidence the energy from
the earthquake dissipated in the
shear walls.
Liquefaction
Liquefaction
Mexico City is a very dangerous in terms of its local
geology. It is currently sitting on a 800 meter (2625 ft) lake
bed made up of silt and volcanic clays that create two
problems that must be address here.
Liquefaction is a type of ground failure in which water
saturated sediment turns from a solid to a liquid as a result
of shaking, often caused by an earthquake or even a volcanic
eruption.
The intense shaking causes the strength of the soil to
become weak and the sand and water begin to flow.
Building Sank into Liquefied Soil
This residential and commercial building sank more than three feet into
the partially liquefied soil.
Loss of
Communication
Media
Central Communications Center





10,000 people lost their lives.
100,000 people were left homeless.
400 buildings are destroyed.
3200 buildings were damaged in the most populous
area of Mexico City.
Total Costs = $4 billion dollars in damages.
Government’s
Proposal for Future
Preparedness

Revisions to the building codes such as:



Improve Emergency Operations:






More Funding for researching dynamic behavior of soil
deposits
Strict evaluation of lateral force design coefficients,
story drifts, and change of natural period of vibration
due earthquake induced structural decay
Emergency Operations should be clear with respect to
rescue
Shelter for the homeless
Lifeline recovery and infrastructure repair
Deployment of volunteer rescue support and forces
need to maintain order
Use of rescue equipment trainings
Impose a more strict licensing control of
professional registration for Engineers and
Scientists.

Most metropolitan areas are ill prepared for
an earthquake of this intensity. Mexico’s
expectations are to advance that level of
preparedness.
The Office of
Disaster
Preparedness in
San Diago
County is
housed in a
2 story building
(7000 ft sq)
It is sitting on
top of 20 lead
impregnated
rubber supports
( base isolators)
That each
weigh 1 ton
Damage to the buildings in Mariana district of San Francisco resulting
from 1980 earthquake.
An apartment building in San Francisco's Marina District was thrown from its foundation and crushed a car in the 1989 earthquake.
The Marina District was the scene of voracious fires caused by broken gas lines.
Photo by Vince Maggiora
In the Santa Cruz
mountains, the
1989 earthquake caused
deep cracks.
"I can't stop shaking," said
one resident.
"I guess I'm surviving, but
I'm scared."
Photo by Deanne
Fitzmaurice
The amplitude of the shaking increases
up the building
Building with long axes perpendicular
to ground motion suffer more shaking
Building with different heights sway at
different frequencies and bank into each
other
A building with different height tend to
break apart


Contained at least 20 sustained cycles of vibrations
with a dominant period of about 2 seconds.
Ground accelerations ranged from 5 – 20% of gravity in a
period range of 1.5 and 3 seconds.
The Universida Nacional Autonomia de Mexico
The Secretaria de Comunication & Transportes site