Why speeds of transverse and longitudinal wave are different even in the same medium ?

What is called a longitudinal wave ?

What is called a transverse wave ?

Statement I: waves genrated in a metal piece can be transverse or longitudinal. statement II: waves generated depend upon the method of creating waves in the metel.

Why do we have different units for the same physical quantity ?

Earthquakes generate sound waves inside the earth. Unlike a gas, the earth can experience both transverse (S) and longitudinal (P) sound wave. Typical the speed of S wave is about 4.0 kms^(-1) , and that of P wave is 8.0km s^(-1) . A seismograph records P and S waves from an earthquake. The first P wave arrives 4min before the first S wave. Assuming the waves travel in straight line, at what distance does the earthquake occur?