Why are magnetic anomalies arranged symmetrically on both sides of oceanic ridges?

The symmetrical arrangement of magnetic anomalies on both sides of oceanic ridges is a direct consequence of seafloor spreading combined with periodic reversals of Earth’s magnetic field.12

This phenomenon is explained by the following process:

• Formation and Magnetization: As new oceanic crust forms at a spreading centre, it cools and becomes permanently magnetized in the direction of the ambient geomagnetic field at that time.12
• Magnetic Reversals: Earth’s magnetic field periodically reverses its polarity. Crust formed during a period of "normal" polarity records a positive magnetic anomaly, while crust formed during a period of "reversed" polarity records a negative anomaly.132
• Symmetrical Spreading: As new magma is intruded at the ridge crest, it splits the previously formed crust. The two halves are pushed outward in opposite directions away from the center.2

Because this process occurs simultaneously on both sides of the ridge, the crustal segments act as a chronological record, creating a mirror-image pattern of magnetic stripes that move away from the ridge over time.12