Question 1: Seismic waves are waves that travel through the Earth, usually caused by earthquakes or other geological events. They carry energy from the source of the disturbance to the Earth's surface and can be classified into different types based on their motion and speed.

Answer: Seismic waves are vibrations that travel through the Earth, caused by earthquakes or geological processes, and transfer energy from the source to the surface.

Question 2: Name the three main types of seismic waves and briefly describe their motion.

Answer: Primary (P) waves are compressional and travel fastest, Secondary (S) waves are shear and slower, Surface waves travel along the Earth's surface causing most damage.

Question 1: Explain why P-waves can travel through both solids and liquids, whereas S-waves can only travel through solids.

Answer: P-waves are compressional waves that cause particles to move in the same direction as wave travel, which allows them to move through solids and liquids; S-waves are shear waves that move particles perpendicular to wave direction and cannot travel through liquids.

Question 1: A seismic wave travels a distance of 300 km through the Earth in 10 minutes. Calculate its average speed in km/h.

Answer: Speed = Distance / Time; = 300 km / (10 min × 60) = 300 km / 600 min; = 0.5 km/min; 0.5 km/min × 60 = 30 km/h

Question 2: If a P-wave has a speed of 8 km/s, how long does it take to travel 160 km?

Answer: Time = Distance / Speed; = 160 km / 8 km/s = 20 seconds

Question 1: Describe a simple experimental setup to simulate seismic wave propagation using a slinky or similar spring. Include the variables you would control and measure, and mention safety precautions.

Answer: A possible setup involves stretching a slinky on a smooth surface and creating vibrations at one end to generate waves. Variables to control include the tension in the slinky and the point of vibration. Variables to measure include wave speed and amplitude. Safety precautions include avoiding excessive tension that could snap the slinky and ensuring no loose clothing or objects near the setup to prevent injury.

Question 1: A seismic station records P-waves arriving 50 seconds after the earthquake shock and S-waves arriving 120 seconds after. If the distance to the earthquake epicentre is calculated based on wave speeds of 8 km/s (P-waves) and 4.5 km/s (S-waves), estimate the distance to the epicentre.

Answer: Using P-wave time: Distance = Speed × Time; = 8 km/s × 50 s = 400 km. Using S-wave time: = 4.5 km/s × 120 s = 540 km. The consistent estimate is approximately 400 km to 540 km; considering the data, the most probable distance is around 400 km.

Question 1: Explain how seismic wave analysis helps in locating earthquake epicentres and assessing their magnitude.

Answer: Seismic wave analysis involves measuring the arrival times of P- and S-waves at different stations. By calculating the distance from each station and triangulating the data, scientists can locate the epicentre. The amplitude and energy of the waves help estimate the earthquake's magnitude.

Question 2: Discuss how understanding seismic waves can improve building design and safety in earthquake-prone areas.

Answer: Knowledge of seismic wave properties allows engineers to design buildings that can withstand the frequency and intensity of seismic vibrations. Techniques include base isolators, damping systems, and reinforcement of structural materials, which reduce damage and protect lives during earthquakes.