Earthquake Epicenter Intensity Calculator
Estimate Modified Mercalli Intensity (MMI) at your location based on earthquake magnitude and distance from the epicenter.
Modified Mercalli Intensity Scale
The Richter or moment magnitude (Mw) scale measures the energy released at the earthquake source. The Modified Mercalli Intensity (MMI) scale measures how strongly shaking is felt at a specific location. MMI depends on both the earthquake magnitude and your distance from the epicenter.
Attenuation Formula
Ground shaking decreases with distance in a predictable way. A simplified attenuation relationship widely used for first estimates:
MMI = M - 2.5 x log10(R) + 1.5
where M is moment magnitude and R is distance from the epicenter in kilometers. This is a rough model; actual shaking depends on local soil conditions, depth, and fault type.
MMI Scale Reference
I: Not felt. II-III: Felt by people at rest, objects may sway. IV: Dishes rattle, felt widely. V: Felt by nearly all, some objects fall. VI: Felt by all, slight structural damage. VII: Difficult to stand, moderate damage to ordinary buildings. VIII: Partial collapse of ordinary buildings, considerable damage to solid structures. IX-X: Severe to violent shaking, many well-built structures destroyed. XI-XII: Catastrophic, few structures standing.
Depth Matters
This calculator uses surface distance to the epicenter. For deep earthquakes (hypocentral depth 50+ km), the actual distance from source to receiver is larger, so real felt intensity at the surface is lower than estimated here. Shallow crustal earthquakes (under 20 km deep) are typically more damaging per unit magnitude.
Soil Amplification
Soft sediment and fill material can amplify ground motion by a factor of 2 to 5 compared to bedrock. The 1989 Loma Prieta earthquake caused disproportionate damage in San Francisco Bay Fill areas far from the epicenter for exactly this reason.