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?
Related
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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.
Related
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?
An earthquake cannot physically occur at a depth of 0 km or -1km (above the surface of the earth). In order for an earthquake to occur, two blocks of crust must slip past one another, and it is impossible for this to happen at or above the surface of the earth. So why do we report that the earthquake occurred at a depth of 0 km or event as a negative depth sometimes? First of all, the depth of an...
What is a Geoid? Why do we use it and where does its shape come from?
A geoid is the irregular-shaped “ball” that scientists use to more accurately calculate depths of earthquakes, or any other deep object beneath the earth’s surface. Currently, we use the “WGS84” version (World Geodetic System of 1984). If Earth were a perfect sphere, calculations of depth and distances would be easy because we know the equations for those calculations on a sphere. However, the...
How are earthquakes recorded? How are earthquakes measured? How is the magnitude of an earthquake determined?
Earthquakes are recorded by a seismographic network. Each seismic station in the network measures the movement of the ground at that site. The slip of one block of rock over another in an earthquake releases energy that makes the ground vibrate. That vibration pushes the adjoining piece of ground and causes it to vibrate, and thus the energy travels out from the earthquake hypocenter in a wave...
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Earthquakes can affect millions of people across the United States. But do you know what causes them? This video will tell you.
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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.
Updated Date: April 10, 2024