Earthquake Waves

• P-waves move faster and are the first to arrive at the surface, these are also called ‘primary waves’.
• The P-waves are similar to sound waves, they travel through gaseous, liquid and solid materials.
• S-waves arrive at the surface with some time lag, these are called secondary waves.
• An important fact about S-waves is that they can travel only through solid materials.
• The surface waves are the last to report on seismograph, These waves are more destructive.
• They cause displacement of rocks, and hence, the collapse of structures occurs.

Volcanoes

• Earth quakes are usually associated with volcanoes, since both are related to plate movements.
• Volcanoes can also happen with ocean-ocean crust collision. Best example is South East Asian Archipelago
• The shield volcanoes are the largest of all the volcanoes on the earth
• These volcanoes are mostly made up of basalt, a type of lava that is very fluid when erupted.

Intrusive Volcanic Landforms

Batholiths

• Batholiths are formed due to the solidification of hot magma inside the earth’s crust, they are in the form of large domes.
• They are the large granitic rock bodies formed at the core of the huge mountains.

Dykes

• At the time of the volcanic eruption, the magma finds its way out through all possible ways like cracks and fissures in the land.
• This magma present in the cracks and the fissures gets cooled in the same position and forms a wall-like structure called Dykes.
• The Dykes are almost perpendicular to the earth’s crust.
• The Dykes are commonly found in the western Maharashtra region.

Types of Earthquake

• Among different types of earthquakes, the most common ones are the tectonic earthquakes, these are generated due to sliding of rocks along a fault plane.
• A special class of tectonic earthquake is sometimes recognized as volcanic earthquake, however, these are confined to areas of active volcanoes.
• In the areas of intense mining activity, sometimes the roofs of underground mines collapse causing minor tremors, these are called collapse earthquakes.
• Ground shaking may also occur due to the explosion of chemical or nuclear devices, Such tremors are called explosion earthquakes.
• The earthquakes that occur in the areas of large reservoirs are referred to as reservoir induced earthquakes.

Volcanic Eruptions

• Basaltic eruptions are characterized by low gas content and low viscosity magmas.
• If the viscosity is low, non-explosive eruptions usually begin with fire fountains due to release of dissolved gases.
• They occur at mid-oceanic ridge and hot spot volcanism. Basalt is highly fluid –mobile and spread across quietly.
• Explosive or andesitic eruptions are favored by high gas content and high.
• Explosive bursting of bubbles will fragment the magma into clots of liquid that will cool as they fall through the air. 
• Andesitic is less fluid mobile and solidifies at short distance due to intense pressure developed inside.