Earthquake Calculator

Earthquake magnitude is logarithmic, so a small numerical change represents a large physical change. A one-unit increase corresponds to ten times the measured ground-motion amplitude on the classic relationship and approximately 31.62 times as much released energy. A two-unit increase corresponds to one hundred times the amplitude and about one thousand times the energy. This calculator applies those ratios to compare a second magnitude directly with a first. The familiar Richter scale was developed for particular instruments and earthquakes in southern California. Modern agencies usually report moment magnitude, written Mw, because it better represents earthquakes across a broad range of sizes. News reports may still use Richter as a familiar general term. Although magnitude scales are designed to be broadly comparable in ordinary discussion, values derived by different methods, stations, and revisions should be compared with appropriate scientific context. Magnitude is not the same as intensity or damage. Magnitude estimates energy released at the source, while shaking at a location depends on distance, depth, fault geometry, ground conditions, building design, and wave propagation. A smaller nearby shallow earthquake can produce stronger local shaking than a larger distant or deep event. Intensity scales describe observed effects at specific places, so one earthquake can have many intensity values but one reported magnitude estimate. When the second magnitude is larger, this page describes greater amplitude and energy with ratios above one. If the second is smaller, the displayed ratios fall below one and indicate its amplitude and energy relative to the first. Magnitudes can be negative for extremely small events because the scale has no physical zero point at magnitude zero. The formulas remain mathematically valid for decimal and negative values as long as both entries refer to compatible magnitude measures. Energy ratios are approximate. The widely used relationship treats radiated seismic energy as scaling with ten raised to one and a half times magnitude difference. Actual energy estimates depend on source physics and measurement method. Do not use this educational comparison for emergency decisions, structural design, or hazard forecasts. Consult official geological agencies for reviewed event data, tsunami information, aftershock guidance, and local safety instructions. The calculator is best used to build intuition about logarithmic scales and to explain why apparently modest magnitude differences represent dramatically different events.