Category: Geography

An earthquake in simple words is the shaking of the earth. It is a natural event and it is caused due to release of energy that generates seismic waves that travel in all directions.

Why does the earth shake?

The shakes are due to the release of energy, that occurs along the fault. The fault is a sharp break in the crustal rocks. These rocks along the fault tend to move in opposite directions. The overlying rocks strata press them and the friction locks them together.

But over time, the tendency to move part over this friction. As a result, these blocks get deformed and slide past each other abruptly. Due to this movement, there is a release of energy and energy waves that travel in all directions.

Hypocentre

The point where the energy is released is called the focus of an earthquake or hypocentre.

Epicenter

The energy waves travel in different directions and reach the surface and the point on the surface, nearest to the focus, is called the epicenter. It is the first one to experience the waves and it is a point directly above the focus.

Types of Earthquakes

• Tectonic Earthquakes
• Collapse Earthquakes
• Explosion Earthquakes
• Reservoir Induced Earthquakes

The most common ones are the tectonic earthquakes which are generated due to the sliding of rocks along a fault plane.

A special class of tectonic earthquakes such as volcanic earthquakes, only volcanic zones.

In the areas of intense mining activity, sometimes the roofs of underground mines collapse causing minor tremors called collapse earthquakes.

Ground shaking may also occur due to the explosion of chemical or nuclear devices called explosion earthquakes.

The earthquakes that occur in the areas of large reservoirs are called reservoir-induced earthquakes.

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 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

Ground Shaking, Differential ground settlement, Land and mudslides, Soil liquefaction, Ground lurching, Avalanches, Ground displacement, Floods from dam and levee failures, Fires, Structural collapse, Falling objects, Tsunami, etc.

The first six listed above have some bearings upon landforms.

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

Tsunamis are waves generated by tremors and not an earthquake in themselves.

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.

The earthquake is a natural hazard. If a tremor of high magnitude takes place, it can cause heavy damage to the life and property of people.

However, not all parts of the globe necessarily experience major shocks

Note that the quakes of high magnitude, i.e. 8+ are quite rare; they occur once in 1-2 years whereas those of ‘tiny’ types occur almost every minute.

Minerals and rocks

The earth is made of different kinds of elements and these elements are in solid form in the outer layer and hot and molten form in the interior of the earth.

Around 98% of the total crust of the earth is composed of eight elements:

1. Oxygen – 46.6%,
2. Silicon- 27.72%,
3. Aluminium – 8.13
4. Iron – 5%
5. Calcium – 3.63%
6. Sodium – 2.83%
7. Potassium – 2.59%
8. Magnesium – 2.09%

Others – 1.41% (Titanium, Hydrogen, Phosphorous, manganese, sulphur, carbon, nickel, etc). There are at least 2000 minerals are identified in the earth’s crust.

But only six major mineral groups are known as Major rock-forming minerals. The rocks are made up of different minerals.

What is Mineral?

The mineral is a naturally occurring substance that is both organic and inorganic in nature.

These substances have an orderly atomic structure and definite chemical and physical properties. Minerals are composed of two or more elements and are also found single such as sulphur, gold, graphite, silver, copper, etc.

Basic Source of Minerals

The basic source of all minerals is the hot magma found in the interior of the earth.

The rocks are formed after the magma cools and then crystals of minerals appear and a systematic series of minerals appear and a systematic series of the mineral are formed.

Fossil fuels such as coal, petroleum, and natural gas are minerals that are organ substances found in Solid, Liquid, and gaseous forms respectively.

Metallic Minerals

Precious Metals – Gold, silver, Platinum, etc

Ferrous Metals – Iron, and other metals mixed with iron to form different kinds of steel.

Non-Ferrous Metals – Metals such as copper, zinc, lead, etc are called Non-Ferrous metals.

Non-Metallic Minerals

The minerals which do not contain metal are called Non-Metallic Minerals.

Example: Sulphur, Phosphates, nitrates, etc.

Cement is made up Non-Metallic Minerals.

Characteristics of Major Minerals

Feldspar

Silicon and oxygen are common elements in all types of feldspar and sodium. Potassium, calcium, aluminium, etc are found in specific feldspar varieties.

Almost half of the earth’s crust is composed of feldspar. Feldspar has a light cream to salmon pink color and it is used in ceramics and glassmaking.

Quartz

Quartz is one of the most important components of sand and granite. It consists of silica and it is a hard mineral virtually insoluble in water.

Quartz is white or colorless and it is used in Radar and radio, and also it is one of the most important components of granite.

Pyroxene

Pyroxene consists of calcium, aluminium, magnesium, iron, and silica. Pyroxene forms 10% of the earth’s crust and is commonly found in meteorites. Its color is green or black.

Amphibole

Aluminium, calcium, silica, iron, magnesium are the main elements of amphiboles. Amphibole forms 7% of the earth’s crust and it is green or black in color and used in the Asbestos industry.

Hornblende is another form of amphiboles.

Mica

Mica comprises potassium, aluminium, magnesium, iron, silica, etc. Mica forms 4% of the earth’s crust and it is commonly found in igneous and metamorphic rocks.

It is used in electrical instruments.

Olivine

Magnesium, iron, and silicon are major elements of olivine. Olivine is used in jewelry and it is usually a greenish crystal, which is often found in basaltic rocks.

Other important minerals are Chlorite, calcite, magnetite, haematite, bauxite, barite, etc.

References

• Landforms (ncert.nic.in)

The Earth’s radius is 6370 km. It is practically impossible to reach the centre of the Earth and conduct research on it. Due to this scientists and engineers are collecting information on the Interior of the Earth based on estimates and inferences from various sources arising from the Earth.

These estimations are classified as Direct Sources and Indirect Sources.

Direct Sources

1. Deep-Sea Drilling

The easily available solid earth materials are surface rocks. There are several deep mining has deep. Deep drilling projects such as the “Deep Ocean Drilling Project” and Integrated Ocean Drilling Project” have to give tons of information about the Interior of the earth.

Deep sea drilling projects have collected rock samples from the ocean floor, which can provide valuable insights into the Earth’s crust and upper mantle. These samples can reveal information about the planet’s geological history, the processes shaping its interior, and the composition of the underlying rocks.

For example, scientists have discovered ancient oceanic crust that provides evidence of plate tectonics and the formation of mountain ranges.

Additionally, drilling programs have uncovered valuable mineral resources, such as oil and gas.

By studying these rock samples, scientist can piece together the puzzle of the Earth’s formation and evolution.

Volcanic eruptions also provided, great information about the interiors. Magma is used for lab analysis. But it is hard to ascertain the depth of the source of such magma.

Deepest Drilled Work

The deepest drill is at Kola, in the Arctic Ocean and the depth is about 12 km.

Indirect Sources

There are also some indirect sources from which we can get information about the interior of the earth. The temperature and pressure increase with increasing distance from the surface towards the interior in deeper depths.

Also, the density of the material also increases with depth. As the thickness of the earth is already known, a scientist has roughly estimated the value of temperature, pressure, and density of materials at varying depths.

By using Meteors, which come from outside the earth used to estimate the interior of the earth. Even though these materials come out of the earth, it is important to note that these things are made up of things that are similar to the ones we find on the earth.

The other indirect sources are Gravitation, Magnetic field, and seismic activities.

Gravitation – Gravitation force (g), which is not equal everywhere. It is greater near the poles and less at the equator.

This is because the equator is from a greater distance away from the center of the earth than the poles.

Also, the gravity values change with the mass of material, the uneven distribution of mass of materials inside the earth influences this value.

Gravity force(g), value change from place to place. This is called Gravity Anomaly. Gravity Anomaly provides us with the value of the distribution of mass of the material in the crust of the earth.

Also, magnetic surveys give us the data about the distribution of magnetic materials in the crustal portion and thereby give information about the distribution of materials in this region.

Also, seismic activities are also important sources to get information regarding the interiors of the earth.

Here’s a table detailing the sources of information about the Earth’s interior, for UPSC preparation:

Indian Standard Time, also known as IST, is the official time observed throughout India. It is calculated based on the standard meridian of India, which is 82°30’E longitude. This Indian Standard Time Meridian passes near Mirzapur in Uttar Pradesh.

As per international timekeeping, IST of India is +5:30 hours ahead of Greenwich Mean Time (GMT) or the Greenwich Meridian. This makes the Indian Standard Meridian unique compared to other countries that follow full-hour time zones.

The clock tower in Mirzapur near Allahabad, Uttar Pradesh, is approximately on the corresponding longitude reference line, and Indian Standard Time is calculated on the basis of 82.3 degrees east longitude. Thus, Indian standard time (IST) refers to the local time of Mirzapur near Allahabad.

In India, the sun rises nearly two hours earlier in the northeast (Arunachal Pradesh) than in the west (Gujarat). This means that people in the east start their day in the dark, and their work hours extend well past sunset. This can disrupt sleep patterns and overall health.

Longitude and Time

Time zones across the globe are derived from the longitude system of the Earth. The Earth is divided into 360° of longitude, and it rotates from west to east, completing one full rotation in 24 hours. This rotation creates the effect of sunrise in the east and sunset in the west.

• There are 180° of longitude both east and west of the Prime Meridian (0°).
• The sun moves across 15° of longitude per hour, meaning 1° of longitude = 4 minutes.
• Thus, as we move eastward, the time increases, and as we move westward, it decreases.

Local Time

Local Time refers to the time observed at a particular location, depending on its longitude. It is calculated with respect to the Greenwich Meridian (0°) and the longitude of the location.

The misalignment of official time with natural daylight leads to wasted daylight hours in the morning and an increased reliance on artificial lighting in the evening. Studies in India have shown that adopting two time zones could lead to significant energy savings. Some regions, like the tea gardens of Assam, have even adopted an unofficial “Chaibagaan time” that is one hour ahead of IST to better utilise daylight.

Example for UPSC Aspirants:

If a place lies at 90° East, what would be the local time when it’s 12:00 noon at Greenwich?

• Difference in Longitude = 90°
• Time Difference = 90 × 4 = 360 minutes = 6 hours
• Local Time = 12:00 noon + 6 hours = 6:00 PM

As the place is east of Greenwich, it adds to GMT. If it were west, we would subtract.

Indian Standard Meridian

To ensure a uniform standard time across the country, countries adopt a Standard Meridian. This is usually a longitude that is a multiple of 7°30’ or 15°, making it easy to express time differences with GMT in whole or half hours. The discrepancy between official time and the sun’s position can lead to a loss of productivity, as people’s natural biological clocks are not in sync with their work schedules.

India’s Standard Meridian:

• The Standard Meridian of India is 82°30’E.
• It is called the Indian Standard Meridian, and IST is based on this longitude.
• This Indian Standard Longitude passes near Mirzapur, not exactly through the centre, but close enough to serve national standard time purposes.

This meridian is commonly referred to in exams like UPSC as Indian Standard Time Meridian or India Standard Time Meridian.

Time Zones and India’s Extent

Although India’s geographical extent spans nearly 30 degrees in longitude (from ~68°E to ~97°E), it follows only one time zone – IST.

• Unlike Russia (11 time zones), the USA (6), and Canada (6), India and China maintain a single time zone to avoid administrative complications.

The Indian standard time line in India, and the line passes through which states

Indian standard time line in India is crucial because it serves as the reference meridian for calculating the single time zone used across all of India. The local time at this meridian is considered the standard for the entire country.

The Indian Standard Time line passes through five states:

1. Uttar Pradesh: The IST meridian is famously recognised for passing through the city of Mirzapur (and nearby Allahabad/Prayagraj), which is often cited as the reference point for calculating.
2. Madhya Pradesh: The line crosses the state, influencing its timekeeping.
3. Chhattisgarh: The meridian passes through the eastern part of the state.
4. Odisha: The IST line runs through a significant portion of Odisha. The Districts through which it moves in Odisha are: Nuapada, Nabarangpur, Koraput, and Malkangiri.

5.Andhra Pradesh: The meridian passes through the southeastern part of Andhra Pradesh.

Using a single standard time zone helps to ensure uniformity and avoid confusion in daily activities, such as railway and flight schedules, despite the country’s vast longitudinal extent.

In the USA and Canada, the time zones often align with states and provinces, which have a high degree of autonomy. This makes it easier for different regions to manage their own economies and social schedules. For example, the business day on the West Coast can overlap with part of the business day on the East Coast, facilitating commerce.

Conclusion

To summarize:

• Indian Standard Time is calculated from the 82°30’E meridian.
• It is +5:30 hours ahead of GMT.
• The IST meridian passes through India, near Mirzapur, and is vital for national synchronisation.
• This single-zone approach, despite India’s vast extent, is a unique administrative decision.
• Understanding the Indian meridian, IST, and the Greenwich Meridian in India is crucial for geography, general awareness, and UPSC preparation.

Also, check the International Date Line

References

• Latitude, Longitude and Time (ncert.nic.in)

Physical Geography

• Solar System
• Earth
  • Latitude and Longitude
  • Motions of Earth – Rotation, Revolution, Inclination of Earth Axis
  • Local and Standard Time
  • International Date Line, Calendar
  • Eclipses
• Interior of the Earth
  • Source of Information – Direct, Indirect – Earth Quakes
  • Volcanoes, crust, mantle, core etc
• Rocks
  • Rocks & landform & Soils
  • Rock Cycle – Types of Rocks – Igneous, Sedimentary, Metamorphic
• Earth Quake
  • Earth Quake and its effect
• Volcano
  • Types and Landforms
• Distribution of continents & Oceans
  • Theories and evidence
    • Continental Drift
    • Post-Drift Studies
    • Ocean Floor Configuration
    • Distribution of Earthquake and Volcanoes
      • Sea Floor Spreading
  • Forces of Drifting
  • Plate Tectonics – Plate Boundaries – Divergent, Convergent and Transform
• Landforms in India and around the world
  • River and Lakes
  • Mountains and Peaks
  • Plateaus
• Geomorphic Process
  • Endogenic Process
    • Diastrophism – Orogenic, Epierogenic, Earthquake, Plate Movement
    • Volcanism – Pacific ring of fire
  • Exogenic Forces
    • Weathering
    • Mass Movement
    • Erosion
    • Transportation & Deposition
  • Landforms and its Evolution
    • Erosional Landforms
      • Erosional landforms of groundwater
      • Erosional landforms of river
      • Erosional landforms of wind
      • Erosional landforms of sea waves
      • Erosional landforms of Glacier
    • Depositional Landforms
      • Depositional landforms of groundwater
      • Depositional landforms of river
      • Depositional landform of wind
      • Depositional landforms of sea waves
      • Depositional landforms of Glacier
  • Composition of Atmosphere
  • Structure of Atmosphere
  • solar radiation heat balance and temperature
    • solar radiation
    • Heating and cooling of atmosphere
    • Factors controlling temperature distribution
    • Distribution of temperature
    • Inversion of temperature
  • Atmospheric Circulation and Weather Systems
    • Atmospheric Pressure
    • Factors affecting speed and direction of wind

Rotation and revolution of earth

Earth has two types of Motions. They are Rotation and Revolution. Rotation is the movement of the earth on its axis. Earth takes 24 hours for one rotation around its axis. This period of rotation is known as Earthday.

Revolution is the movement of the earth around the sun in a fixed path or orbit. Earth motion around the sun in its orbit, which the earth takes 365 days which is measured as 1 year. Also, 6 Hours is ignored for convenience.

These 6 Hours are saved every year to make one day (24 Hours) and this extra day is added to the month of February. Thereby every 4th year there will be 29 days instead of 28 days. The year with 366 days is called a leap year.

The Axis of the Earth is an imaginary line, which makes an angle of 66° with its orbital plane. An Orbital Plane is a plane formed by orbit.

Effects of Motion of Earth

The earth receives sunlight from the sun. Only half side of the earth receives sunlight at one point and the other of the earth does not receive sunlight.

The side that receives sunlight is the Day, the side which does not receive Sunlight is the night. This is because of the Spherical shape of the earth.

The circle of Illumination is the circle which divides the day from night on the Sphere of Earth (Globe). This circle does not coincide with the axis.

Seasons of Earth

The season in the Earth is caused by the inclination of the earth in the same direction and revolution around the sun in an elliptical orbit. Every year is divided into Summer, winter, spring, and autumn seasons.

The change of season is because of the earth’s position around the Sun.

Summer Solstice

The Northern Hemisphere is tilted towards the sun on 21st June. The Sunrays fall directly on the Tropic of Cancer, the areas near the Tropic of Cancer receive more heat.

The regions near the Poles receive less heat are the Sun rays fall of Poles are Slanting. The North Pole which is inclined towards the Sun and the areas beyond the Arctic circle experiences continuous daylight for six months.

The Summer occurs North of the equator, as the large portion of the Northern Hemisphere is getting Sunlight. At these places, on June 21, the longest day and the shortest night occurs.

In the Southern Hemisphere, this condition is opposite, where the Southern Hemisphere has winter, where the Nights are longer than the days. The above-mentioned points are all the characteristics of Summer Solstice.

Winter Solstice

On 22nd December, the Tropic of Capricorn receives direct rays of the Sun. This is because the South Pole is tilted towards the Sun.

As the result, the rays of the Suns fall vertically at the Tropic of Capricorn which is 23° S and by this Southern Hemisphere receives more sunlight. Therefore, it is Summer in Southern Hemisphere and Winter in Northern Hemisphere.

The Days in the Southern Hemisphere is longer than the Nights. This position of the earth is called Winter Solstice. Australia is a good example for Winter Solstice, and it has Summer during December and celebrates the Christmas festival in the Summer Season.

Equinox

During Equinox, the direct Sun Rays fall on the equator. At this position, neither the North Pole and the south pole is tilted towards the Sun. As a result, the whole earth experiences equal days and equal nights.

This position of the earth is called the Equinox. It happens on 21st March and September 23.

On September 23, it is Spring season in the Southern Hemisphere and Autumn in the Northern Hemisphere. On March 21, it is Spring season in the Northern Hemisphere and Autumn in the Southern Hemisphere.

References

• Motion of the Earth – Ncert