How would magnetic stripes grow wider?

Magnetic stripes are the term for a phenomenon found predominately in oceanic crust, which is the term for a type of rock found in the Earth's tectonic plates. Crust is the generalized name for the uppermost portions of the rock (those farthest from the core) which have solidified, and oceanic refers to these rocks typically originating beneath the ocean, at regions called mid-ocean ridges, or sometimes rifts. 

Ridges are essentially cracks in between tectonic plates,...

Magnetic stripes are the term for a phenomenon found predominately in oceanic crust, which is the term for a type of rock found in the Earth's tectonic plates. Crust is the generalized name for the uppermost portions of the rock (those farthest from the core) which have solidified, and oceanic refers to these rocks typically originating beneath the ocean, at regions called mid-ocean ridges, or sometimes rifts. 

Ridges are essentially cracks in between tectonic plates, through which molten rock from the earth's mantle can travel. This action tends to add rocky material to the plates on either side of the ridge, in turn pushing those plates away from the ridge, at more or less equal speed.

One property of this type of rock is its tendency to align itself with the earth's magnetic field as it cools. Additionally, the Earth's magnetic field has reversed itself abruptly many times throughout history. If two oceanic rocks that had formed during opposite magnetic field states were inspected, they would appear to have opposite records of the magnetic field. When seen at a larger scale, this is described through analogy as "stripes" - with each of the stripes corresponding to rock that formed when the earth had a particular field alignment, with adjacent stripes having the opposite alignment.

The width of these stripes could be increased in two ways;

1. The longer the Earth's magnetic field stays in one alignment, without a reversal, the longer the currently-forming oceanic rock would represent this as it cools. 


2. If oceanic rock formed more rapidly, it would lay down a larger amount of material per unit time that would record the current magnetic field alignment.