Mexico 1985 Earthquake

8/6/2019 Mexico 1985 Earthquake

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Mexico City Earthquake


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Background19 September 1985, 7:18 am

50km off the coast of Mexico, on the

Pacific Ocean bed. 8.1 Richter Scale


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Liquefaction

- The process where water-saturated, unconsolidated soil acts more

like a dense fluid than a solid

- Caused by strong ground motion during an earthquake

- Occurs when a material of solid consistency is transformed, with

increased water pressure, into a liquefied state

- This caused the ground to behave like jelly and vibrate with the

shock waves, worsening the extent of the damage


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Resonance

- Another reason behind the massive damage was the resonance

in the lakebed sediments, or natural period

- All objects have a natural period, or the time it takes to swingback and forth, from point A to point B and back again

- As seismic waves move through the ground, the ground also

moves at its natural period

- When the building or ground has a similar natural period, they

are said to resonate, amplifying the shock waves and this will

lead to disaster


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- During this earthquake, the natural

period of the seismic waves and that

of some 5 to 14-storey buildings were

similar, and this caused most

buildings of that height to collapse

- In contrary, many buildings of 1-5

floors of height and above 15 floors

remained relatively undamaged

- For example, the 54-storey Torre

Latinoamericana building survived the

earthquake almost undamaged


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Earthquake Death Toll, Injuries and Damage

- According to official estimates, 10,000 people were killed, 50,000

were injured, and 250,000 people were left homeless

- In Mexico City alone, 412 buildings collapsed and 3,124 others wereheavily damaged

- The earthquake also caused landslides in other states

- Total cost of the damage amounted to around US$3-4 billion dollars

(1985 currency rate), with most of the damage caused by the

earthquake


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- Number of people with potable water decreased from 6 million to

90,000

- 200,000 jobs were lost

- 40% of the population were without electricity, and 70% were

without telephone service

- of the available public hospital beds were destroyed when

hospitals collapsed, making it much harder for treatment for the

wounded to be administered


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- Extensive damage of the twelve-storey high Ministry of

Communications and Transport resulted in the near total collapse

of long-distance communications between Mexico City and the restof the world, complicating coordination of international rescue

efforts

- The maximum estimate on the Mercalli damage intensity scale was

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Preparedness

Effective national programmes should require each school organisation

and every individual school to take measures to reduce risks and to

prepare employees and students to react in safe ways during

emergencies. These school safety elements should include the

following:


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Education. Develop and teach curricula for primary and secondary

school students on earthquakes, societal issues relating to

earthquakes and preparedness actions. Use the school curricula to

promote a culture of prevention in future generations of the

community.

Risk reduction measures. Undertake measures to improve the

safety of the physical environment by bracing and anchoring

furnishings, bookcases, and equipment and building components

such as lights, heaters and water heaters.


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Emergency plan. Prepare and maintain plans that identify the

actions, decisions and responsibilities needed before, during and

following an earthquake; the organisation and responsibilities to

carry out these plans, including determining whether to shelter or

release students or to use school facilities as community shelters;

and the equipment and supplies needed to carry out these

decisions.

Safety assessments. Establish standards, line of responsibility and

procedures to assess the safety of buildings following earthquakes,

and decide on evacuation, repair and re-occupancy procedures.


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Training. Provide training and materials for employees and

students on earthquake hazards and actions to take to improve

personal safety.

Drills. Hold periodic drills simulating realistic conditions of

earthquake events to reinforce training and to test the adequacy of

plans and safety assessments.


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Model implemented to help decrease the extent

of damage done by earthquake

Invention of Mexico Earthquake Model- comprehensive assessment of

all the seismic sources in Mexico, including the subduction zone along

Mexicos southwestern coast and crustal background sources.

Determines the level of ground shaking at a particular site utilizing

ground motion attenuation equations selected based on an inclusive

survey of research publications and consultations with local

seismologists


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A spectral response-based approach to damage assessment

provides a robust link between ground motion and building

damage. The spectral response methodology captures the effects

of construction type, building height, local site conditions, and

ground shaking based on earthquake magnitude and location to

realistically assess a buildings response to an earthquake.

Hazard data, including soil type and susceptibility to liquefaction, is

stored using a proprietary RMS geographic indexing system known

as the variable resolution grid (VRG).


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Differentiates between 12 distinct source segments along the

Middle America Trench subduction zone

Soil hazard data for the entire country, with high resolution soil andliquefaction data for Mexico City

Special amplification parameters to account for long-period effect

for sites on old lake deposits in Mexico City

Spectral response methodology to realistically assess a buildings

response to an earthquake based on earthquake magnitude and

location


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Building vulnerability curves developed using local expertise and

RMS research

Accounts for local/regional construction differences, building codechanges

Like this, the damage done by the earthquake will be reduced.


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Prediction on flow of debris- Photogrammetric techniques have been used for decades in

Mexico to evaluate hazards.

- Geologists use digital photogrammetry for fast evaluation of

natural hazards at volcanoes.

- Digital elevation models by using photogrammetric software is

applied to calculating ice volume and water equivalent in order to

predict debris flows resulting from quick melting of the glacier on

Popocatpetl volcano.

- The methodology is useful in dangerous situations where field workis not possible, and remote techniques are needed to rapidly

provide data on hazards.


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Protection Make sure the building structure is in conformity with city

government construction requirements.

Obtain the services of construction specialists who haveexperience in earthquake prevention before you begin construction

of a home or building.

Identify the location of all gas, water and electrical lines. Use

flexible connectors and become familiar with the proceduresnecessary to disconnect these lines.


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Large pieces of furniture must be attached firmly to the wall as it

might become hazards in case of an earthquake, such as cabinets,

mirrors, bookcases, or shelving. Avoid placing heavy objects on

such large pieces of furniture. Make sure that big light fixtures and

chandeliers are securely mounted to the ceiling.

Always carry identification with you. Include basic health

information, such as blood type, medications, allergies, and who to

contact in case of an emergency

Every building should have a written contingency plan. Become

familiar with it, and perform periodic evacuation drills with your

family. Do not wait until you are caught, all of the sudden, without

knowing what to do or how to react in case of an earthquake.


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Prediction

30 seismic monitors were installed in states of Guerrero and

Michoacn .

On Sept. 19, 1985, these strong-motion sensors recorded an

earthquake of magnitude 8.1.

It was the first time digitally recording an earthquake of a great

magnitude.


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Measures of prediction to be used in future

Animal early warning


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Measures of prediction to be used in future

Animal early warning

- In folklore, some animals have been identified as

being more able to predict earthquakes up to afew days before it occurs.

- Unusual behaviour from several species of

animals are indicators.

- It is their response to an increase in low-

frequency electromagnetic signals which could not

be detected by humans.


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Measures of prediction to be used in futureUsefulness of earthquake history

- Measure accumulation of strain in rocks surrounding a fault relative

to the amount of strain released in the last quake.

- This provides a measure of how much more the rocks can

withstand before another quake.

- Prediction will be more accurate, enabling people of affectedregions to react on time, reducing the extent of damage.


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Mitigation

- Disaster mitigation can be defined as

Measures taken in advance to reduce

the impact of a disaster.

- Includes structural measures such as

safer building construction.

- As well as non-structural measures such

as education, training and technologytransfer.


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Mitigation

- Ensure that building structure is in conformity with citygovernment construction requirements.

- Hire efficient construction specialists whom have experience inearthquake prevention

- Education: Drills are conducted to educate and familiarise peopleon what to do in the event of an earthquake.

- Also, posters could be put up at places of soft soil or low-lyingcoastal areas where tsunamis occur. Can be used to educatepublic.

Documents

Mexico 1985 Earthquake