The first wave appear after 320 seconds and after the arrival of P wave
We can use the formula TD = d × t / 100 km
TD = d × t / 100 km
= ( 4000 km × 8 s ) / 100 km
= 32000 km /s / 100 km
= 320 seconds
The first s-wave will arrived in 320 seconds after the arrival of the first p-wave
The earliest waves to reach a seismograph are known as P waves, or primary waves. The fastest seismic waves, known as P waves, can pass through solid, liquid, or gas. On the medium they travel through, they leave a trail of compressions and rarefactions
The second waves to arrive during an earthquake are called S waves, or secondary waves. They can only pass through solids and are substantially slower than P waves
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