Is This An Earthquake?

Understanding earthquake magnitudes and how often earthquakes happen

The earth shakes more than you may think.

Small earthquakes happen frequently but often go unnoticed. Large quakes strike less frequently but with devastating effects.

Check the table below to appreciate how often the earth may be moving beneath your feet—or to better understand what’s happening in an area struck by an earthquake. You may be surprised to learn how many times the Earth quakes each year.

Magnitude Earthquake Descriptor
(Rough Number
per Year)
Intensity (MMI)
Near Epicenter
MMI Description
Less than 3.0 Micro (1 million +) I I. Not felt.
3.0-3.9 Minor (100,000) II-III II. Felt by some under favorable conditions.

III. Felt indoors especially on upper floors of buildings. Vibration akin to light trucks passing by the building.
4.0-4.9 Light(10,000) IV-V IV. Felt outdoors by few. Sensation like a heavy truck passing by the building.

V.Felt by nearly everyone. Small unstable objects shifted or upset.
5.0-5.9 Moderate (1,500) VI-VII VI. Felt by all. Many are frightened and run outdoors. A few instances of fallen plaster or damaged chimneys. Damage is slight.

VII.Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable in poorly built or badly designed structures.
6.0-6.9 Strong (140) VII-IX VIII. Damage slight in specially designed structures; considerable in ordinary substantial buildings with partial collapse. Damage great in poorly built structures.

IX. Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings.Buildings shifted off foundations.
7.0-7.9 Major (15) VIII and higher  X. Most masonry and frame structures and some well-built wooden structures destroyed. Rails bent.
8.0 or greater Great (1) XI. Few masonry structures remain standing. Rails bent greatly.

XII. Damage nearly total.

* MMI: Modified Mercalli Intensity. The magnitude and MMI relation are very approximate and assume that the earthquake occurs very near the site where the MMI is measured. While magnitude and intensity are interdependent to some degree, there is no exact correlation between them. For example, an earthquake might have a low magnitude, but because of poor soil conditions or building construction, it might cause a great deal of damage, and thus exhibit relatively high intensity.

Table is adapted from FM Global’s “Protecting Your Facility From the Dangers of Earthquakes,” which used the United States Geological Survey (USGS) publication, Magnitude/Intensity Comparison and has been updated to incorporate the latest USGS Earthquake Statistics.

During a 10-year period, roughly 75 percent of the earthquake losses at FM Global client facilities were attributed to shake damage. The remaining 25 percent were mostly attributable to fire protection system damage. However, geological failures (e.g., landslide or subsidence) can contribute significantly to earthquake loss at some locations. Prepare now to better withstand earth movement.

What you can do in your facility now:

  • Where possible, secure any objects that are important, tall, or slender by installing anchors through holes at the base of each object.
  • Install automatic earthquake-activated shut-off valves where flammable gas or ignitable liquid are piped into buildings.
  • Survey your existing fire protection systems to see if they meet the recommended earthquake provisions. In particular, confirm sprinkler risers have four-way braces and mains that are well braced, both perpendicular and parallel, to the pipe.
  • Incorporate earthquake response into emergency response team (ERT) activities.

FM Global Clients:

  • Involve FM Global in new construction projects, fire protection system installations, or modifications and alterations to existing protection.
  • Contact your FM Global client service team to find out about earthquake risk at your location and additional engineering services.

For more information, download or view:

FM Global’s Emergency Checklist: Earthquake

Protecting Your Facility From the Dangers of Earthquakes