How can an earthquake have a negative magnitude?
Magnitude calculations are based on a logarithmic scale, so a ten-fold drop in amplitude decreases the magnitude by 1.
If an amplitude of 20 millimetres as measured on a seismic signal corresponds to a magnitude 2 earthquake, then:
- 10 times less (2 millimetres) corresponds to a magnitude of 1;
- 100 times less (0.2 millimetres) corresponds to magnitude 0;
- 1000 times less (0.02 millimetres) corresponds to magnitude -1.
An earthquake of negative magnitude is a very small earthquake that is not felt by humans.
What was the duration of the earthquake? Why don't you report the duration of each earthquake? How does the duration affect the magnitude?
What does it mean that the earthquake occurred at a depth of 0 km? How can an earthquake have a negative depth; that would mean it’s in the air. What is the geoid, and what does it have to do with earthquake depth?
How are earthquakes recorded? How are earthquakes measured? How is the magnitude of an earthquake determined?
Moment magnitude, Richter scale - what are the different magnitude scales, and why are there so many?
What is the difference between magnitude and intensity? What is the Modified Mercalli Intensity Scale?
How do you determine the magnitude for an earthquake that occurred prior to the creation of the magnitude scale?
The USGS Earthquake Hazards Program recently released a new strategic plan for earthquake monitoring entitled the “Advanced National Seismic System – Current Status, Development Opportunities, Priorities, 2017-2027.”
The Hawaiian Volcano Observatory’s 1912–2012 Centennial—100 Years of Tracking Eruptions and Earthquakes
HAWAI‘I ISLAND, Hawaii —The history of earthquakes and seismic monitoring in Hawai‘i during the past century will be the topic of a presentation at the University of Hawai‘i at Hilo on Thursday, January 26, at 7:00 p.m.
USGS will Grant Universities $5 Million to Beef Up Public Safety Grants totaling $5 million under the American Recovery and Reinvestment Act are being awarded to 13 universities nationwide to upgrade critical earthquake monitoring networks and increase public safety.
USGS map displaying intensity of potential ground shaking from natural and human-induced earthquakes. There is a small chance (one percent) that ground shaking intensity will occur at this level or higher. There is a greater chance (99 percent) that ground shaking will be lower than what is displayed in these maps.
USGS charts showing the number of earthquakes greater than or equal to magnitude 2.7 since 1980 in the five focus areas identified as having especially high ground-shaking hazard in the central and eastern U.S. in 2017.
This map shows earthquakes above magnitude 4.0 in the eastern United States since 1973, the first year with a complete catalog. There are 184 earthquakes recorded. An earthquake of magnitude 4.0 or greater can cause minor or more significant damage. The circle sizes correspond to earthquake magnitude, ranging from 4.0 to 5.9 (the largest was in the Gulf of Mexico).