EARTHQUAKE

Earthquakes

·         An earthquake is a vibration or oscillation of the surface of the earth caused by the elasticity or the isostatic adjustment of the rocks, beneath the surface of the earth.

·          It may be caused by human as well as natural activities.

·         Before the earthquake waves hit a region, the amount of 'Radon' gas increases in the atmosphere of that region.

·          Therefore, rise in the concentration of 'Radon gas' over the atmosphere of a region indicates that the region is going to be hit by an earthquake. But a correlation is not yet firmly established

·         According to a moderate estimate about 30,000 earthquakes occur every year. But most of these are so slight that we cannot feel them. There is no visible damage from them. But every year there are some earthquakes of great intensity and magnitude.

HYPOCENTRE

·         The point below the surface of the earth, from where the seismic (earthquake) waves originate is called the ‘Focus’ of the earthquake.

EPICENTRE

·         The place, perpendicularly above the focus on the surface.

·         The energy dissipated from the focus is called the ‘Elastic Energy’.

·         The waves generated during an earthquake are called Seismic Waves, which are classified into 3 types:

i)                    Primary or Longitudinal Waves.

·         These are simply known as P-Waves.

·         These are longitudinal waves analogous to the sound waves.

·         These waves have the maximum velocity among the three types of seismic waves.

·         These waves can pass through the solid as well as liquid mediums, though their velocity gets slowed down in the liquid medium.

ii)                  Secondary or Transverse Waves.

·         These are also called as S-Waves.

·         These are transversal waves analogous to the light waves.  

·         These waves can travel only through the solid medium and disappear in the liquid medium.

·         Since these waves do not pass through the core being in liquid state.

iii)                Surface or Long Period Waves.

·         These are also known as 'L' waves which originate when 'P' wave hits the surface.

·          These waves affect only the surface of the earth.

·         These are the most destructive and cover the longest distance among the three types of waves.

Cross-Section of the Earth-Paths of ‘P’ Waves;

‘S’ Waves; and Surface Wave

·         In the Earth's interior the shock- or P waves travel much faster than the S waves (approx. relation 1.7 : 1)

·          In solid rock P-waves travel at about 6 to 7 km per second; the velocity increases within the deep mantle to ~13 km/s.

·         The velocity of S-waves ranges from 2–3 km/s in light sediments and 4–5 km/s in the Earth's crust up to 7 km/s in the deep mantle.

·          As a consequence, the first waves of a distant earthquake arrive at an observatory via the Earth's mantle.

·          S waves and later arriving surface waves do main damage compared to P waves. P wave squeezes and expands material in the same direction it is traveling.

·         S wave shakes the ground up and down and back and forth

·         P and S waves travel in pairs.

·         As a rule of thumb, the distance to the earthquake epicentre is the number of seconds between the P and S waves multiplied by 8.

·         By tracing the path and the motion of these waves, information about the earth's interior can be gathered.

·         On the basis of the depth of the earthquakes, it can be divided into three groups–

a)      Moderate Earthquake.0-50 km

b)      Intermediate Earthquakes. 50-250 km

c)      Deep Focus Earthquakes.250 — 700 km.

On the basis of the causative factors, the earthquakes may be classified into-

a)         Natural Earthquakes- Caused due to natural factors. Further divided into

                    i.            Volcanic Earthquakes

                  ii.            Tectonic Earthquakes

·         Tectonic earthquakes are caused by the sudden earth movements, generally along faults, usually at depths varying from about 4.5 km to 24 km below the earth's surface. Majority of natural earthquakes including the most powerful and damaging ones belong to this category.

                iii.            Isostatic Earthquakes

                iv.            Plutonic Earthquakes

·         Plutonic earthquakes are deep focus earthquakes, the depth of disturbances being between 250 km and about 700 km.

b)         Artificial or Man-made Earthquakes.

·         Caused due to human activities, such a construction of roads, dams and reservoirs, storage of huge volumes of water behind the dams, nuclear explosions etc.

·         On the basis of the human casualties the earthquakes can be classified as –

a)      Moderately Hazardous Earthquakes – below 50,000 person

b)      Highly Hazardous Earthquakes – 51,000 – 1,00,000 person

c)      Most Hazardous Earthquakes – above 1,00,000 person

Seismographs

·         The instruments the seismic waves, which help us to measure the intensity of an  earthquake are called 'Seismographs'– Different scales are used to measure the intensity of earthquakes such as

1.      Rossy-Feral Scale– This scale measures the earthquakes between 1 to 10 units.

2.      Mercalli Scale– It is an empirical scale, It is divided into 12 units.

3.      Richter Scale–

·         It is a mathematical (logarithmic) scale, which measures the intensity of an earthquake between 0 to 9.

·         For each unit of increase in the Richter Scale, the amplitude of the earthquake wave increases by a factor of 10.

4.      The Medvedev–Sponheuer–Karnik scale,

·         also known as the MSK or MSK-64, is a macroseismic intensity scale used to evaluate the severity of ground shaking on the basis of observed effects in an area of the earthquake occurrence.

Earthquake is measured in following scales

Intensity / Severity of earthquake → Measured by MMS (Modified Mercalli Scale)

• It measures the effects of an earthquake. It is distinct from the moment magnitude (Mw) usually reported for an earthquake, which is a measure of the energy released
• The magnitude or intensity of an earth quake is measured in relation to its effect on human life..
• The Mercalli scale quantifies the effects of an earthquake on the Earth's surface, humans, objects of nature, and man-made structures on a scale from I (not felt) to XII (total destruction).
•  Values depend upon the distance from the earthquake, with the highest intensities being around the epicentral area.

Magnitude of earthquake (Energy released at epicenter) → Measured by Richter scale

·         Magnitude is the amount of energy released and is based on the direct measurement of the size of seismic wave

·         The two scales have different applications and measurement techniques. The Mercalli scale is linear and the Richter scale is logarithmic. i.e. a magnitude 5 earthquake is ten times as intense as a magnitude 4 earthquake.

Variation in direction of waves → 

·         Measured by Seismograph

Isoseismal Lines

·         The lines Joining the regions of same seismic intensity arc called as Isoseismal Lines.

Homoseismal Lines

·          The lines joining the places which experience the earthquake tremors at the same time called Homoseismal Lines.

World Distribution of Earthquakes

·         A close view on the world map showing the distribution of earthquakes reveals that the earthquakes are associated with the weaker and isostatically disturbed areas of the earth.

·          Most of the world earthquakes occur along-

a)      Different plate margins and

b)      The zones of faulting and fracturing

 Different earthquake belts of the world are–

A.     Circum-Pacific Belt:

·         This belt accounts for about 65% of the total earthquakes of the world.

·          In this belt the earthquakes originate mostly beneath the ocean floor near the coast.

·         The Circum- Pacific Belt represents the convergent plate boundaries where the most widespread and intense earthquakes occur.

·          The regions included in this belt are Chile, California, Alaska, Japan, Philippines, New Zealand.

·         This belt presents four ideal conditions for the earthquakes to occur, viz, interaction between the continental and oceanic plate margins, isostatic disturbance due to the presence of young fold mountains, vulcanicity and subduction of oceanic plate below the continental plate.

·          Here, the earthquakes are directly related to faults or fractures of the rock strata and to the active volcanoes.

B.     Mid-Continental Belt:

·         This belt accounts for about 21% of the total earthquakes of the world. This belt is also known as Mediterranean or Alpine – Himalayan Belt.

·         This belt represents the weaker zones of folded mountains where isostatic and fault-induced earthquakes occur.

·         Starting from Mexico and crossing the Atlantic Ocean, this belt extends to Alps, Caucasus, Himalayas and then turns towards south and in the region of South-eastern islands it culminates into the Circum-Pacific belt.

·         Seismic zone of India is a part of this belt.

C.     Mid-Atlantic Ridge Belt:

·         This belt records moderate and shallow focus earthquakes.

·         The earthquakes in this region are caused due to creation of transform faults and the fractures because this region represents the divergent plate margin.

·         This belt extends from Iceland in the north to Bouvetova Island in the south.

·         Most of the earthquakes in this belt occur near the equator.

D.     Other Regions:

·         In this, the region from the great rift valley of Africa and Gulf of Aden to the Arabian Sea is included.

·         The earthquake belt of the Indian Ocean is also included in this belt.

Tsunami

·         'Tsu-na-mi' is a Japanese word which means on coming oceanic waves. These waves are very long and with less oscillation which originatein the oceans due to earthquakes that occur on the ocean-bed.

·         The movement of water with the Tsunami waves is upto complete depth which makes them more catastrophic.

·          From the Tsunami point of view, Pacific Ocean is in the most dangerous position. These are the most powerful in the convergence zone of the oceanic plates.

·         The tsunami that occurred on the 26^th of December2004 in the Sumatra island of Indonesia in the Indian Ocean was the result of subduction of Indian plate below the Burmese plate.

·         The intensity of the earthquake was recorded at 8.9, which caused catastrophic tsunami waves.

·         Eleven countries, including Indonesia, Malaysia, Sri Lanka and India came under the influence of these waves.  

·         Nagapattinam district in Tamil Nadu was the most affected area in India.

·         In October 2007, India started the most advanced Tsunami Warning System. India provide information received from it to its neighbour countries.

·         The system reveal the intensity, depth and centre of the tsunami.

·         It provide the information of every earthquake tremor of Indian Ocean in 20 minutes, after calculation, to the nearest regions.

·         The system installed at Hyderabad, the Indian National Centre for Ocean and Information Services (INCOIS) and operational since 2007

Indian National Center for Ocean Information Services (INCOIS)

·         is an autonomous organization of the Government of India, under the Ministry of Earth Sciences, located in Pragathi Nagar, Hyderabad.

·         ESSO-INCOIS was established as an autonomous body in 1999 under the Ministry of Earth Sciences (MoES) and is a unit of the Earth System Science Organization (ESSO).

·         ESSO- INCOIS is mandated to provide the best possible ocean information and advisory services to society, industry, government agencies and the scientific community through sustained ocean observations and constant improvements through systematic and focussed research.

Seismic Activities and disaster management in India

·         The Himalaya, its foot hills and the north Indian plain are the most sensitive regions from the point of view of seismic activity.

·         This is due to the fact that the Indian plate is ceaselessly pushing the Eurasian plate.

·          Therefore, , this is the most unbalanced region which is frequented by the earthquakes.

·          This region has experienced several earthquakes since the last century such as in Assom, Kangra, Bihar, Nepal and Uttarkashi.

·         The peninsular plateau region of India, which was generally considered stable from the geological point of view and was known to be an earthquake- free region till recently, has also been hit by earthquakes, e.g., the 1993 Latur earthquake in Maharashtra.

·         This shook the belief that the Peninsular region is geologically stable and balanced.

·         Now, no part of India is considered earthquake-free region, because the northward movement of the Indian plate generates forces which give rise to energy waves in the interior part of the plateau region.

·         When this energy tires to come out, it creates conditions for the formation of faults in the Indian plate.

·          This is the reason that many faults have developed in the geologically stable Peninsular India where there is a chance of heavy earthquake.

·         The reason for the Bhuj earthquake of Kachachha region in 2001 was its being situated in the earthquake prone (zone V) region.

·         Moreover, the interaction between several fragments of the plate generates forces, which causes earthquake.

·         Due to the combined effect of being situated in the fault region and northward movement of the Indian plate, the earthquake was very intense, measuring 6.9 in the Richter scale.

·          Many a time, earthquakes are caused by human activities as well.

Human activity

·          Big dams create isostatic imbalance, thereby forces are generated causing earthquakes in the nearby areas.

·         For example the 1967 earthquake in Koyna, Maharashtra.

·          Nuclear test explosions also, generate forces which cause earthquakes.

·          In the mountainous region, if the structure of the rocks is not surveyed properly while constructing the roads, it causes landslides which trigger the earthquakes.

·         Non availability of safety measures also makes the impact of earthquakes very serious.

·         Whereas, on the one hand, the earthquakes in Japan, generally with an intensity of 7 on the Ricther scale, do not lead to much great loss, on the other hand, the earthquakes in India, which may be just 5 on the Richter scale, produce serious dangers.

·         Unscientific construction works and weak and sub-standard houses further add to the dangers which cause great loss of life and wealth.

·          Prof Vinod Kumar Gaur of the Indian Astro-Physics Institute has advised that there is a need of scientific evaluation of disaster in all earthquake prone areas.

Measures to reduce  impact of earthquake

·         To reduce the dangers and possibility of earthquakes, proper planning and attention should be paid towards land-use and various construction activities in these areas.

·          People can be made aware of earthquakes by mass-awareness and educational programmes.

·         Over-populated areas can be evacuated well in time by providing timely warnings.

·         Transportation, communication and power projects can be shut down.

Prediction

·          Latest developments in the field of science and technology viz. Sensor Designing, Telemetry Online Computing and better communication can be used scientifically to reduce the intensity of loss to life and property caused by an earthquake.

·         Although there is no system in India to get pre-information about earthquakes, now this is becoming possible to know the early information about the earthquakes due to some researches.

·         Moderate earthquakes can be mesaured by Seismophone, Microphone and other remote equipments.

·         Other ways to measure the earthquakes are the water level changes in well, waves rise and temperature change in the well, behavioural changes in animals and geological disturbances occurred in the focus of the earthquakes.

·         Autoness water level recorder will provide the information about the disturbances in water on internet on the interval of every 15 minutes through the Telemetry networking on the basis of which geologists are expecting the possibility of forecasting about the earthquakes.

·          As per the research, one to three hours early information about the earthquakes would be  possible.

·         Forecasting of the earthquakes can also the made through the geological disturbance of the country which will depend totally on the understanding of the seismic zones.

·         At present sufficient knowledge has been obtained regarding the geomorphological structure of the Himalayan region and the plate tectonics activity, and regarding the other earthquake prone areas in India as well.

·          Efforts have also been made by the Indian standards Bureau to update the direction-providing earthquake-maps of the Indian Meteorological Department.

·         In the map, the available geomorphological and tectonic data are re-evaluated to bring about accuracy in determining the earthquake-prone regions of India.

·         To study and assess the risks of earthquakes, topographical maps and satellite surveys are also being used.

·         The National Disaster-Management Commission has been constituted as a premier body which prepares short term and long term strategies to tackle and manage various disasters including earthquakes.

·         It has political, administrative and technical departments which are busy working upon the allotted assignments.

·          Efforts are being made in the earthquake-prone regions for pre-emptive measures for the safety.

·         The 2001 earthquake in Bhuj witnessed mass scale loss of life and property mainly because of the lack of such a mechanism.

·          Therefore short term and long term safety measures are being emphasised upon. Japan is providing technical support.

·         Anti-earthquake housing and disaster management if sufficiently available, can reduce- the risk of loss due to earthquakes to quite an extent.

Tiny gravity changes can be picked up much faster than seismic waves.

·         During an earthquake, every extra second of warning can save lives. Earthquakes cause tiny changes to Earth's gravity, and new research suggests these signals can be detected almost instantaneously at the start of an earthquake, offering a much earlier warning than the seismic waves we currently rely on.

·         Researchers examined gravity data collected in Japan around the time of the 2011 Tohoku-Oki earthquake, which generated the devastating tsunamis leading to the Fukushima Daiichi Nuclear Power Plant disaster.

·          They were looking for a signal that preceded the arrival of seismic waves, and they found one, opening the door for new developments in earthquake early warning systems.

Did meteorites create the Earth’s tectonic plates?

Modelling by O’Neill and his colleagues has thrown up a possible answer.

·         The research, led by Craig O’Neill from the university’s Planetary Research Centre, and published in the journal Nature Geoscience, offers a scenario to illuminate what happened during the first 500 million years of the Earth’s existence – a period known as the Hadean, or, more poetically, the geologic dark ages.

·         “Our results indicate that giant meteorite impacts in the past could have triggered events where the solid outer section of the Earth sinks into the deeper mantle at ocean trenches – a process known as subduction,” he says.

·         “This would have effectively recycled large portions of the Earth’s surface, drastically changing the geography of the planet.”

Online reference material

·         http://geology-guy.com/teaching/iac/animations/

·         http://geology-guy.com/teaching/iac/animations/seismograph.htm

·         http://ndma.gov.in/images/guidelines/national-dm-policy2009.pdf

·         http://ndma.gov.in/images/policyplan/dmplan/National%20Disaster%20Management%20Plan%20May%202016.pdf

Earthquake Zoning in India:

Effects of an earthquake is measured by descriptive scale namely Modified Mercalli intensity scale or the Medvedev-Sponheuer-Karnik scale.

• Based on the likelihood of occurrence of damaging earthquakes, a seismic zone map has been prepared to spot the critical regions in India .
• The seismic zone map has been subdivided India into 5 zones – I, II, III, IV and V. The seismic shaking intensity is expected maximum in zones marked as V and higher.
• The seismic zone maps are updated regularly with strict reference to geology, the seismotectonics and the seismic activity in the country.

Zone 5

• Zone 5 covers the areas with the highest risks zone that suffers earthquakes of intensity. It is referred to as the Very High Damage Risk Zone. The state of Kashmir, the western and central Himalayas, the North-East Indian region and the Rann of Kutch fall in this zone. Generally, the areas having trap or basaltic rock are prone to earthquakes.

Zone 4

• This zone is called the High Damage Risk Zone. The Indo-Gangetic basin and the capital of the country (Delhi), Jammu and Kashmir fall in Zone 4. In Maharashtra the Patan area (Koyananager) is also in zone 4.

Zone 3

• The Andaman and Nicobar Islands, parts of Kashmir, Western Himalayas fall under this zone. This zone is classified as Moderate Damage Risk Zone.

Zone 2

• This region is classified as the Low Damage Risk Zone. 

Zone 1

• Rest of the country. Very low damage risk zone.

National Centre for Seismology (NCS)

• The National Center for Seismology is an office of the Indian Ministry of Earth Sciences. The office provides earthquake surveillance and hazard reports to governmental agencies. It includes five divisions:

·         Earthquake Monitoring & Services,

·         Earthquake Hazard & Risk Assessment, Geophysical Observation System.

·         Operates national seismological network with 84 stations.

·          These stations are connected to NCS headquarter through VSAT for real time data communication.

·         In the event of an earthquake NCS locates them using data from its network and disseminate earthquake parameters to all the concerned government department and other stake holders through SMS, email and fax.

·         However this causes some delay in dissemination and also restricts the number of recipients.

In India's Western Ghats, geologists are drilling some of Asia's deepest boreholes in an audacious attempt to unlock the mysteries of earthquakes. Scientific Deep Drilling started in 2016

• Mountains are ideal places to set up water reservoirs for generating electricity, but water pressure can build up in the pores of the Earth and stress the crust to danger levels.
• Quakes can also be triggered by mining, fracking (hydraulic fracturing to recover gas and oil from shale rock) or extracting water from under the ground.
• Geologists believe there are more than 100 sites around the world where quakes have been triggered by filling of water reservoirs.
• At Koyna, geologists say, earthquake activity began after the reservoir was filled with more than a trillion litres of water in 1962. Seismologist Harsh K Gupta says the Koyna region "is the best site anywhere in the world where an earthquake can be observed".
• Indian geologists were clearly inspired by an ambitious experiment by US scientists to drill directly into the San Andreas quake zone for a unique view of how earthquakes work. The crack in the Earth's surface, which runs through California, is one of the most studied faults on the planet.

Objective

• aimed at setting up of borehole observatory (s) at depth for directly measuring the in situ physical properties of rocks, pore fluid pressure, hydrological parameters, temperature and other parameters of an intra-plate, active fault zone in the near field of earthquakes - before, during and after their occurrence, leading to a better understanding of the mechanics of faulting, physics of reservoir triggered earthquakes and preparation of a predictive model.
• Borehole Geophysics Research Laboratory (BGRL), Karad has undertaken scientific deep drilling and associated investigations in the Koyna seismic zone, Maharashtra.

Drilling deep boreholes for scientific research is not uncommon.

• In Iceland, geologists have drilled into the heart of a volcano. Scientists have also embarked on a controversial initiative to drill into a supervolcano beneath the Gulf of Naples.
•  In 1961, American scientists attempted to drill into the mantle, which makes up the bulk of the planet's volume and mass.
• The deepest scientists have managed to penetrate is 12km at the Kola Superdeep Borehole in Russia - a paltry 0.2% of the way to the centre of the Earth.

Mobile App – India quake

• To overcome this, a Mobile App has been developed by the NCS for automatic dissemination of earthquake parameter (location, time and magnitude) after the occurrence of earthquakes.
• The App will make information dissemination faster with no restrictions on the number of recipients. Any citizen can download this App and get the real time earthquake location information on his/her mobile.
• Other than scientific and administrative benefits of the App, it will help in reducing panic amongst people during an earthquake.
• For example, if an earthquake occurs in Hindukush region, Afghanistan and is strongly felt in Delhi, then people in Delhi will know in less than 2 minutes that the earthquake has actually occurred in Afghanistan and not in Delhi.

Other activities

Probabilistic Seismic Hazard Analysis(PSHA) of 40 selected cities:

• Under a project sanctioned to IIT, Kharagpur Probabilistic Seismic Hazard Analysis (PSHA)of 40 cities has been performed for probable integration with other hazard attributes on GIS platform.
• PSHA for 40 cities has been carried out based on underlying seismogenic source zones in the Indian subcontinent employing the earthquake catalogue, supplemented by records of historical earthquakes

Active Fault Mapping:

• Identification of an active fault is critical for realistic assessment of the seismic hazard, particularly for critical structures like nuclear facilities, large dams, and defence installations.
• A major programme on Active Fault Mapping (AFM) has been initiated to map and characterize the active faults in the country and to prepare a library of active fault data that would help in undertaking seismic hazard assessment in different parts of the country.
 Three areas, namely, North-west and Central Himalaya, North-east Himalaya and Kachchh regions have been selected as priority areas to start with.

What to Do Before an Earthquake

• Repair deep plaster cracks in ceilings and foundations. Get expert advice if there are signs of structural defects.
• Anchor overhead lighting fixtures to the ceiling.
• Follow BIS codes relevant to your area for building standards
• Fasten shelves securely to walls.
• Place large or heavy objects on lower shelves.
• Store breakable items such as bottled foods, glass, and china in low, closed cabinets with latches.
• Hang heavy items such as pictures and mirrors away from beds, settees, and anywhere that people sit.
• Brace overhead light and fan fixtures.
• Repair defective electrical wiring and leaky gas connections. These are potential fire risks.
• Secure water heaters, LPG cylinders etc., by strapping them to the walls or bolting to the floor.
• Store weed killers, pesticides, and flammable products securely in closed cabinets with latches and on bottom shelves.
• Identify safe places indoors and outdoors.
• Under strong dining table, bed
• Against an inside wall
• Away from where glass could shatter around windows, mirrors, pictures, or where heavy bookcases or other heavy furniture could fall over
• In the open, away from buildings, trees, telephone and electrical lines, flyovers and bridges
• Know emergency telephone numbers (such as those of doctors, hospitals, the police, etc)
• Educate yourself and family members

Have a disaster emergency kit ready

• Battery operated torch with extra batteries
• Battery operated radio
• First aid kit and manual
• Emergency food (dry items) and water (packed and sealed)
• Candles and matches in a waterproof container
• Knife
• Chlorine tablets or powdered water purifiers
• Can opener.
• Essential medicines
• Cash and credit cards
• Thick ropes and cords
• Sturdy shoes

Develop an emergency communication plan

• In case family members are separated from one another during an earthquake (a real possibility during the day when adults are at work and children are at school), develop a plan for reuniting after the disaster.
• Ask an out-of-state relative or friend to serve as the 'family contact' after the disaster; it is often easier to call long distance. Make sure everyone in the family knows the name, address, and phone number of the contact person.

Help your community get ready

• Publish a special section in your local newspaper with emergency information on earthquakes. Localize the information by printing the phone numbers of local emergency services offices and hospitals.
• Conduct week-long series on locating hazards in the home.
• Work with local emergency services and officials to prepare special reports for people with mobility impairment on what to do during an earthquake.
• Provide tips on conducting earthquake drills in the home.
• Interview representatives of the gas, electric, and water companies about shutting off utilities.
• Work together in your community to apply your knowledge to building codes, retrofitting programmes, hazard hunts, and neighborhood and family emergency plans.

What to Do During an Earthquake

Stay as safe as possible during an earthquake. Be aware that some earthquakes are actually foreshocks and a larger earthquake might occur. Minimize your movements to a few steps that reach a nearby safe place and stay indoors until the shaking has stopped and you are sure exiting is safe.

If indoors

• DROP to the ground; take COVER by getting under a sturdy table or other piece of furniture; and HOLD ON until the shaking stops. If there is no a table or desk near you, cover your face and head with your arms and crouch in an inside corner of the building.
• Protect yourself by staying under the lintel of an inner door, in the corner of a room, under a table or even under a bed.
• Stay away from glass, windows, outside doors and walls, and anything that could fall, (such as lighting fixtures or furniture).
• Stay in bed if you are there when the earthquake strikes. Hold on and protect your head with a pillow, unless you are under a heavy light fixture that could fall. In that case, move to the nearest safe place.
• Use a doorway for shelter only if it is in close proximity to you and if you know it is a strongly supported, load bearing doorway.
• Stay inside until the shaking stops and it is safe to go outside. Research has shown that most injuries occur when people inside buildings attempt to move to a different location inside the building or try to leave.
• Be aware that the electricity may go out or the sprinkler systems or fire alarms may turn on.

If outdoors

• Do not move from where you are. However, move away from buildings, trees, streetlights, and utility wires.
• If you are in open space, stay there until the shaking stops. The greatest danger exists directly outside buildings; at exits; and alongside exterior walls. Most earthquake-related casualties result from collapsing walls, flying glass, and falling objects.

If in a moving vehicle

• Stop as quickly as safety permits and stay in the vehicle. Avoid stopping near or under buildings, trees, overpasses, and utility wires.
• Proceed cautiously once the earthquake has stopped. Avoid roads, bridges, or ramps that might have been damaged by the earthquake.

If trapped under debris

• Do not light a match.
• Do not move about or kick up dust.
• Cover your mouth with a handkerchief or clothing.
• Tap on a pipe or wall so rescuers can locate you. Use a whistle if one is available. Shout only as a last resort. Shouting can cause you to inhale dangerous amounts of dust.

Measuring Earthquakes

·         The earthquake events are scaled either according to the magnitude or intensity of the shock. The magnitude scale is known as the Richter scale. The magnitude relates to the energy released during the quake. The magnitude is expressed in absolute numbers, 0-10. The intensity scale is named after Mercalli, an Italian seismologist. The intensity scale takes into account the visible damage caused by the event. The range of intensity scale is from 1-12.

EFFECTS OF EARTHQUAKE

Earthquake is a natural hazard. The following are the immediate hazardous effects of earthquake:

(i) Ground Shaking

(ii) Differential ground settlement

(iii) Land and mud slides

(iv) Soil liquefaction

(v) Ground lurching

(vi) Avalanches

(vii) Ground displacement

(viii) Floods from dam and levee failures

(ix) Fires

(x) Structural collapse

(xi) Falling objects

(xii) Tsunami

·         The first six listed above have some bearings upon landforms, while others may be considered the effects causing immediate concern to the life and properties of people in the region.

·          The effect of tsunami would occur only if the epicentre of the tremor is below oceanic waters and the magnitude is sufficiently high.

·         Tsunamis are waves generated by the tremors and not an earthquake in itself.

·         Though the actual quake activity lasts for a few seconds, its effects are devastating provided the magnitude of the quake is more than 5 on the Richter scale.