A seismologist records that the frequency of earthquakes of magnitude 4 or higher in a region follows a logarithmic scale: each unit increase in magnitude represents a tenfold decrease in frequency. If there are 500 such earthquakes annually at magnitude 4, how many magnitude 6 earthquakes occur per year?

Wed, 06 May 2026 20:03:48 +0000

**Why Magnitude 6 Earthquakes Are So Rare—Even When Magnitude 4 Is Common** A growing audience of curious learners is exploring how natural forces follow precise mathematical patterns—one such pattern governs earthquake frequency across different magnitudes. A seismologist records that each upward unit on the Richter scale means a tenfold drop in how often earthquakes of that size or higher occur. This logarithmic scaling explains why magnitude 4 quakes are common, but events of magnitude 6 are far less frequent. Understanding this scale reveals deeper insights into seismic risk, infrastructure resilience, and long-term preparedness. ### The Science Behind Earthquake Frequency Each full magnitude increase cuts earthquake occurrences by a factor of ten. A magnitude 5 quake is ten times more frequent than magnitude 6, and a magnitude 6 quake occurs roughly ten times less often than magnitude 5. This rapid decline continues logarithmically across scales. It’s not just a number game—it’s a fundamental principle shaping how scientists model seismic hazards nationally.