Question 1: Define seismic waves and distinguish between primary and secondary seismic waves.

Answer: Seismic waves are elastic waves that travel through the Earth as a result of earthquakes. Primary waves (P-waves) are longitudinal and travel faster, while secondary waves (S-waves) are transverse and slower.

Question 2: Explain how seismic waves are used to determine the Earth's internal structure.

Answer: Seismic waves are detected at various locations, and their travel times and paths are analysed to infer the layers and composition of Earth's interior, as different materials affect wave speed and behaviour.

Question 1: A seismic wave travels through the Earth covering a distance of 3000 km in 20 minutes. Calculate its average speed in km/h.

Answer: Speed = Distance / Time = 3000 km / (20 min × 1/60 hr) = 3000 km / (1/3 hr) = 9000 km/h

Question 2: If a primary seismic wave has a speed of 8 km/s and the earthquake occurs at a depth of 40 km, how long does it take for the wave to reach the surface?

Answer: Time = Distance / Speed = 40 km / 8 km/s = 5 seconds

Question 1: Describe the key variables that need to be controlled when setting up a laboratory experiment to simulate seismic wave propagation.

Answer: Variables include the material properties (elasticity, density), wave source strength, distance between source and detector, and environmental factors such as temperature and vibrations.

Question 2: Identify three safety precautions that should be taken when conducting theoretical experiments involving seismic wave generation and detection.

Answer: Ensure proper handling of equipment to prevent injury, avoid exposure to loud noise levels or vibrations that could cause harm, and operate equipment within safe limits to prevent damage.

Question 1: A seismic station records P-waves arriving at 12 seconds and S-waves arriving at 22 seconds after an earthquake. Explain what this time difference indicates about the distance from the earthquake epicentre to the station.

Answer: The time difference indicates the distance; a larger difference signifies a greater distance from the epicentre because P-waves travel faster than S-waves.

Question 2: Given that the average speed of P-waves is 8 km/s and S-waves is 4.5 km/s, estimate the distance to the earthquake epicentre based on the recorded arrival times.

Answer: Difference in arrival times = 10 seconds. Using P-wave speed: Distance = 8 km/s × 12 s = 96 km. Alternatively, using S-wave speed: 4.5 km/s × 22 s = 99 km. Averaging gives approximately 97.5 km.

Question 1: Explain how seismic wave analysis helps in assessing earthquake risk and in designing earthquake-resistant structures.

Answer: Seismic wave analysis provides data on wave speeds and intensities, helping engineers understand potential ground motions. This information guides the design of structures that can withstand seismic forces, reducing damage and safeguarding lives.

Question 2: Describe how advances in seismic wave technology can improve early warning systems for earthquakes.

Answer: Advances such as real-time data processing, deployment of dense sensor networks, and improved signal analysis algorithms enable faster detection of seismic waves. This can provide critical seconds to minutes of warning before destructive waves arrive, allowing for protective actions and reducing casualties.