Normal fault কী?

Example 14.8 (A slow and a fast ridge)

In a million years the East Pacific Rise at $30{}^{\circ}$ South makes $14.6\,\mathrm{cm}/\mathrm{yr} \times 10^6\ \text{years} = 146\,\mathrm{km}$ of new ocean floor, $73\,\mathrm{km}$ on each side; the Mid-Atlantic Ridge at the same latitude makes $33\,\mathrm{km}$, $16.5\,\mathrm{km}$ on each side. The deep hole of the eastern Pacific went into crust made at more than $20\,\mathrm{cm}$ a year, among the fastest spreading ever recorded.