Interior of the Earth

Structure of the Earth's Interior

• The Earth's interior is divided into several layers, including the crust, mantle, outer core, and inner core.
• The crust is the outermost solid layer, ranging in thickness from 5 km to 70 km.
• The mantle is the layer beneath the crust, extending from the Moho's discontinuity to a depth of 2,900 km.
• The outer core is a liquid layer, while the inner core is a solid layer made up of heavy materials like nickel and iron.

Earthquake Waves

• Earthquake waves are generated by the release of energy at the focus of an earthquake.
• There are two types of earthquake waves: body waves and surface waves.
• Body waves are generated due to the release of energy at the focus and move in all directions through the body of the Earth.
• Surface waves are generated by the interaction of body waves with the surface rocks and move along the surface.
• P-waves are a type of body wave that moves faster and are the first to arrive at the surface.
• S-waves are another type of body wave that can only travel through solid materials and arrive at the surface with some time lag.

Shadow Zone

• The shadow zone is an area where earthquake waves are not reported.
• The shadow zone is different for each earthquake.
• The study of different events reveals that for each earthquake, there exists an altogether different shadow zone.
• The shadow zone of P-waves appears as a band around the Earth between 105° and 145° away from the epicentre.
• The shadow zone of S-waves is much larger than that of P-waves.

Types of Earthquakes

• Tectonic earthquakes are the most common type, generated due to the sliding of rocks along a fault plane.
• Volcanic earthquakes are a special class of tectonic earthquakes, confined to areas of active volcanoes.
• Reservoir-induced earthquakes occur in areas of large reservoirs.
• Collapse earthquakes occur when the roofs of underground mines collapse.
• Explosion earthquakes are caused by the explosion of chemical or nuclear devices.

Effects of Earthquakes

• Ground shaking is a major effect of earthquakes.
• Other effects include differential ground settlement, land and mud slides, soil liquefaction, and structural collapse.
• Tsunamis can occur if the epicentre of the earthquake is below oceanic waters and the magnitude is sufficiently high.

Measuring Earthquakes

• Earthquake events are scaled according to magnitude or intensity.
• The magnitude scale is known as the Richter scale, which measures the energy released during the quake.
• The intensity scale is named after Mercalli, which takes into account the visible damage caused by the event.

Volcanoes

• Volcanoes are classified based on the nature of eruption and the form developed at the surface.

• Shield volcanoes are the largest type of volcanoes on Earth, characterized by low-explosivity and gentle slopes.

• Cinder cone volcanoes are formed by the accumulation of ash and cinder from small-scale eruptions.### Volcanic Landforms

• Trap formations cover a larger area than present-day formations and develop into cinder cones

• Mid-Ocean Ridge Volcanoes occur in oceanic areas, with a system of mid-ocean ridges over 70,000 km long that experiences frequent eruptions

Composite Volcanoes

• Characterized by eruptions of cooler and more viscous lavas than basalt
• Often result in explosive eruptions, with large quantities of pyroclastic material and ashes accumulated in the vicinity of vent openings
• Formations resemble composite volcanoes, with lava and pyroclastic material building up around the vent

Volcanic Rocks

• Formed from lava that cools and solidifies, either on the surface or in the crust
• Classified as volcanic rocks (cooling at the surface) and plutonic rocks (cooling in the crust)

Intrusive Forms

• Formed when lava cools within the crustal portions, assuming different shapes
• Examples include batholiths, lacoliths, phacoliths, sills, and dykes

Batholiths

• Large bodies of magmatic material that cool in the deeper depths of the crust, developing into large domes
• Appear on the surface only after denudational processes remove overlying materials
• Cover large areas and can assume depths of several km, with granitic bodies

Lacoliths

• Large dome-shaped intrusive bodies with a level base and connected by a pipe-like conduit from below
• Resemble surface volcanic domes of composite volcanoes, with a localized source of lava

Phacoliths and Sills

• Near-horizontal bodies of intrusive rocks found at the base of synclines or top of anticlines in folded igneous country
• Called phacoliths, with a definite conduit to the source beneath in the form of magma chambers
• Thinner ones are called sheets, while thick horizontal deposits are called sills

Dykes

• Formed when lava makes its way through cracks and fissures in the land, solidifying almost perpendicular to the ground
• Develop a wall-like structure, with examples found in the western Maharashtra area
• Considered the feeders for eruptions that led to the development of the Deccan traps