Emphasize the many forms of seismic waves and talk about the formation of shadow zones. (Answer in 200 words)
Lala RamLearner
Resources & Suggestions
Mains Answer Writing Latest Articles
On: February 24, 2025
Daily Answer Writing Practice Questions (24 February 2025)
The rise of the work-from-home culture has brought about several ethical issues in private organizations. In this context, do you believe it is ethical for an employee to engage in moonlighting? Discuss. (Answer in 150 words) घर से काम करने ...
On: February 22, 2025
Comments:
0
Indo-US Relation: Areas of Cooperation & Conflicts
Key Areas: Defense, technology, trade, energy, and regional cooperation. Key Areas of Cooperation 1. Defense and Security Transition from buyer-seller to co-production and technology sharing. India as a Major Defense Partner (MDP) and inclusion in STA-1. Access to advanced technologies, ...
On: February 22, 2025
Comments:
0
भारत-अमेरिका संबंध: सहयोग और संघर्ष के क्षेत्र
मुख्य विषय: भारत-अमेरिका संबंधों की मजबूती, विशेषकर रक्षा, प्रौद्योगिकी और क्षेत्रीय सहयोग में प्रगति। सहयोग के प्रमुख क्षेत्र 1. रक्षा एवं सुरक्षा सहयोग भारत और अमेरिका के बीच रक्षा संबंधों का विस्तार। प्रमुख रक्षा साझेदार (MDP) का दर्जा और STA-1 ...
According to United States Geological Survey (USGS)- “Earthquake waves or seismic waves are the vibrations that travels through the earth’s crust and mantle, caused by the sudden movement of rocks during an earthquake.”
Types of Earthquake waves –
a) Primary Waves – These are compressional waves which travel through solid, liquid and gas .It causes ground compression and expansion.
b) Shear Waves -These are shear waves which travel only through solid materials.These are slower than primary waves.It causes ground deformation and shaking.
a) Rayleigh waves- These are rolling waves and these are most destructive wabe type which causes ground motion in circular motion.
b) Love waves – These are horizontal waves which cause ground motion perpendicular to direction of travel.They are less destructive than Rayleigh waves.
Emergence of Shadow Zones –
a)P-Wave Shadow Zone (105° to 145 ° from epicenter).
b)S-Wave Shadow Zone (105° to 105° from epicenter).
Understanding these waves and shadow zones will help the scientists in studying earth’s internal structure , predicting earthquake behaviour and will improve their hazard assessment.
Earthquake waves also referred as the Seismic Waves. Two main types of seismic waves are generated during the quakes are as follows:
S / Secondary / Transverse / Shaking waves – Travelling through solid only & changes occurs only in shape & not in volume. Slower than P waves. Mode of propagation is back & forth at the right angle to the direction of motion of the wave. It “shakes” the particles at the right angle to their direction of travel, hence also known as Shear waves.
Refraction phenomenon shown by the seismic waves, and tend to refracted at boundaries within the earth, at the Core-Mantle Boundary (CMB). The place on Earths part where no Body waves detected is generally called as the Shadow Zone which is existed because the material of the earth’s interior is not uniform in rigidity.
When seismic wave’s changes its speed is depend upon the rigidity of the Earth’s interior. Wave is also bending & changes their directions as they pass through the different material. S wave does not travel through the liquid; they are disappearing at the CMB.
P wave can travel through all layers of the earth, the speed & direction of the P wave change as the wave pass through each medium or layer. The wave bends in such a way that P wave shadow zone is formed.
Shadow Zone covers the side of the Earth that is opposite an earthquake / seismic source. It covers the angular distance from the seismic source to the shadow zone is 105˚ on either side, so the total angular distance is the 145˚.
Earthquake waves also referred as the Seismic Waves. Two main types of seismic waves are generated during the quakes are as follows:
S / Secondary / Transverse / Shaking waves – Travelling through solid only & changes occurs only in shape & not in volume. Slower than P waves. Mode of propagation is back & forth at the right angle to the direction of motion of the wave. It “shakes” the particles at the right angle to their direction of travel, hence also known as Shear waves.
L / Love Waves – With greater wavelength & also known as Long Waves. Originated from epicenter & cause rock to move side by side. Perpendicular to the direction in which the waves are travelling. Rayleigh Waves – are causing the rocks/ground to move with elliptical or rolling movements.
Emergence of Shadow zones – Sudden changes in the speed of seismic waves are known as the Seismic Discontinuities. It helps in discovery of fundamental inference in the material of the Earth’s interior by analyzing the arrival time of the P waves.
P wave traveled a relatively slow route through the material within about 20 km of surface. Second P waves were traveled at the greater depth & reached at the deeper zone where the velocity of the P waves abruptly increased.
Refraction phenomenon shown by the seismic waves, and tend to refracted at boundaries within the earth, at the Core-Mantle Boundary (CMB). The place on Earths part where no Body waves detected is generally called as the Shadow Zone which is existed because the material of the earth’s interior is not uniform in rigidity.When seismic wave’s changes its speed is depend upon the rigidity of the Earth’s interior. Wave is also bending & changes their directions as they pass through the different material. S wave does not travel through the liquid; they are disappearing at the CMB.
P wave can travel through all layers of the earth, the speed & direction of the P wave change as the wave pass through each medium or layer. The wave bends in such a way that P wave shadow zone is formed.
Shadow Zone covers the side of the Earth that is opposite an earthquake / seismic source. It covers the angular distance from the seismic source to the shadow zone is 105˚ on either side, so the total angular distance is the 145˚.
Answer: Earthquake waves, also called seismic waves, are basically of two types- body waves and surface waves. Body waves are generated due to the release of energy at the focus and move in all directions traveling through the body of the earth. Body waves are of two types:
When body waves interact with the surface rocks, they generate a new set of waves called surface waves. These waves move along the surface. They cause displacement of rocks, and hence, the collapse of structures occurs. Surface waves are of two types:
Shadow zone: Though earthquake waves get recorded in seismographs located at far-off locations, there exist some specific areas where the waves are not reported. Such zones are called ‘shadow zones’. It was observed that seismographs located at any distance within 105° from the epicenter, recorded the arrival of both P and S-waves. However, the seismographs located beyond 145° from the epicenter, record the arrival of P-waves, but not that of S-waves. Thus, a zone between 105° and 145° from the epicenter was identified as the shadow zone for both types of waves. The entire zone beyond 105° does not receive S-waves. The shadow zone of the S-wave is much larger than that of the P-waves and is a little over 40 percent of the earth’s surface.
Seismologists have concluded that the emergence of the shadow zone is because of the internal structure of the earth which is not homogeneous. Earth’s interiors have an uneven density which leads to the emergence of shadow zones. The shadow zone of P waves has led to the identification of boundaries between the mantle and core. Further, it has also been deduced that the outer core is made of liquid, as S-waves cannot travel through liquid mediums and P-waves are refracted by the liquid core. Thus, the concept of the shadow zone has helped seismologists get information about the interior of the earth’s surface.