Whether you’ve never experienced an earthquake, are in the midst of intense shaking, or just felt a temblor, there are valuable resources available to help. Watch the video to learn more.
What reference datum is used for earthquake depths?
The USGS currently uses the WGS84 Geoid as the reference datum for earthquake depths. Other seismic networks might or might not use different methods.
The choice of reference datum depends on the method used to locate the earthquake, which varies by seismic network. The Advanced National Seismic System Comprehensive Earthquake Catalog (ComCat) includes data from many different seismic networks, so the process for determining the depth is different for different events. Earthquake depth can be relative to:
- The WGS84 geoid
- Mean sea-level
- The average elevation of the seismic stations that provided arrival-time data for the earthquake location
Depth is the least-constrained parameter in an earthquake's location; the error bars are generally larger than the variation due to different depth determination methods.
Learn More: NOAA - What is the Geoid?
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Epicenter Hypocenter Diagram
Diagram showing the epicenter and hypocenter.
The epicenter is the point on the earth's surface vertically above the hypocenter (or focus), point in the crust where a seismic rupture begins.
Diagram showing the epicenter and hypocenter.
The epicenter is the point on the earth's surface vertically above the hypocenter (or focus), point in the crust where a seismic rupture begins.
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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?
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Diagram showing the epicenter and hypocenter.
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Diagram showing the epicenter and hypocenter.
The epicenter is the point on the earth's surface vertically above the hypocenter (or focus), point in the crust where a seismic rupture begins.