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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 Earth more closely approximates an ellipsoid, which is what a ball looks like if you sit on it. Ellipsoid calculations aren’t as easy as spherical calculations, but they’re still well-known and do-able. Be that as it may, we all know that the earth is not really an ellipsoid because there are oceans, and mountains, and valleys, and many other features that are not part of an ellipsoid.
The geoid is an imaginary sea level surface that undulates (has a wavy surface) over all of the earth; it isn’t just for the oceanic areas, it also extends through the land masses.
You can generalize the relationship between the ellipsoid, the geoid, and the actual shape of the earth with this:
geoid + ellipsoid = Earth
Learn More: NOAA - What is the Geoid?
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...
Earthquake size, as measured by the Richter Scale is a well known, but not well understood, concept. The idea of a logarithmic earthquake magnitude scale was first developed by Charles Richter in the 1930's for measuring the size of earthquakes occurring in southern California using relatively high-frequency data from nearby seismograph stations. This magnitude scale was referred to as ML , with...
Magnitude scales, like the moment magnitude, measure the size of the earthquake at its source. An earthquake has one magnitude. The magnitude does not depend on where the measurement is made. Often, several slightly different magnitudes are reported for an earthquake. This happens because the relation between the seismic measurements and the magnitude is complex and different procedures will often...
For earthquakes that occurred between about 1890 (when modern seismographs came into use) and 1935 when Charles Richter developed the magnitude scale, people went back to the old records and compared the seismograms from those days with similar records for later earthquakes. For earthquakes prior to about 1890, magnitudes have been estimated by looking at the physical effects (such as amount of...
When an earthquake occurs, one of the first questions is "where was it?" The location may tell us what fault it was on and where damage (if any) most likely occurred. Unfortunately, Earth is not transparent and we can't just see or photograph the earthquake disturbance like meteorologists can photograph clouds. When an earthquake occurs, it generates an expanding wavefront from the earthquake...
The duration of an earthquake is related to its magnitude but not in a perfectly strict sense. There are two ways to think about the duration of an earthquake. The first is the length of time it takes for the fault to rupture and the second is the length of time shaking is felt at any given point (e.g. when someone says "I felt it shake for 10 seconds" they are making a statement about the...
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)...
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...
It is relatively easy to acquire the necessary materials and build your own seismometer. The links here are to various sources with information on how to build a seismometer. They range from very simple and inexpensive to sophisticated and pricey. Model Seismograph - Classroom Demonstration Build your own Seismograph Station Build Your Own Seismograph Amateur Seismology Homebuilt Seismograph FAQ
A seismometer is the internal part of the seismograph, which may be a pendulum or a mass mounted on a spring; however, it is often used synonymously with "seismograph". Seismographs are instruments used to record the motion of the ground during an earthquake. They are installed in the ground throughout the world and operated as part of a seismographic network. The earliest "seismoscope" was...
The earliest seismoscope was invented by the Chinese philosopher Chang Heng in A.D. 132. This was a large urn on the outside of which were eight dragon heads facing the eight principal directions of the compass. Below each dragon head was a toad with its mouth opened toward the dragon. When an earthquake occurred, one or more of the eight dragon-mouths would release a ball into the open mouth of...
Plots showing Mauna Loa ground deformation and earthquake monitoring data between midnight August 1 and midnight August 3, 2022. The top panel shows ground tilt in microradians at station MOK, on the northwest side of Mauna Loa’s summit caldera. A histogram showing the number of located earthquakes that occurred per hour is shown in the middle panel.
Plots showing Mauna Loa ground deformation and earthquake monitoring data between midnight August 1 and midnight August 3, 2022. The top panel shows ground tilt in microradians at station MOK, on the northwest side of Mauna Loa’s summit caldera. A histogram showing the number of located earthquakes that occurred per hour is shown in the middle panel.
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.
Earthquakes at Mount Rainier from 2010 to 2019. As shown in the graphic, fluids from the magmatic system beneath the volcano rise through existing cracks and weaknesses in the crust. Along with rainwater and ice/snow melt, these fluids combine to create a hydrothermal system within the volcano.
Earthquakes at Mount Rainier from 2010 to 2019. As shown in the graphic, fluids from the magmatic system beneath the volcano rise through existing cracks and weaknesses in the crust. Along with rainwater and ice/snow melt, these fluids combine to create a hydrothermal system within the volcano.
Graphic shows the earthquake swarm from June-July, 2019, compared to previous swarms detected in March 2019, 2017, 2016, and in 2014. The activity is likely the result of small-scale underground movements of hydrothermal fluids or gas — a sign that Mount St. Helens remains an active volcano.
Graphic shows the earthquake swarm from June-July, 2019, compared to previous swarms detected in March 2019, 2017, 2016, and in 2014. The activity is likely the result of small-scale underground movements of hydrothermal fluids or gas — a sign that Mount St. Helens remains an active volcano.
Locations (Lat, Long, Depth) of January 17, 2010, earthquake swarm on Madison Plateau, Yellowstone National Park.
Locations (Lat, Long, Depth) of January 17, 2010, earthquake swarm on Madison Plateau, Yellowstone National Park.
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...
Earthquake size, as measured by the Richter Scale is a well known, but not well understood, concept. The idea of a logarithmic earthquake magnitude scale was first developed by Charles Richter in the 1930's for measuring the size of earthquakes occurring in southern California using relatively high-frequency data from nearby seismograph stations. This magnitude scale was referred to as ML , with...
Magnitude scales, like the moment magnitude, measure the size of the earthquake at its source. An earthquake has one magnitude. The magnitude does not depend on where the measurement is made. Often, several slightly different magnitudes are reported for an earthquake. This happens because the relation between the seismic measurements and the magnitude is complex and different procedures will often...
For earthquakes that occurred between about 1890 (when modern seismographs came into use) and 1935 when Charles Richter developed the magnitude scale, people went back to the old records and compared the seismograms from those days with similar records for later earthquakes. For earthquakes prior to about 1890, magnitudes have been estimated by looking at the physical effects (such as amount of...
When an earthquake occurs, one of the first questions is "where was it?" The location may tell us what fault it was on and where damage (if any) most likely occurred. Unfortunately, Earth is not transparent and we can't just see or photograph the earthquake disturbance like meteorologists can photograph clouds. When an earthquake occurs, it generates an expanding wavefront from the earthquake...
The duration of an earthquake is related to its magnitude but not in a perfectly strict sense. There are two ways to think about the duration of an earthquake. The first is the length of time it takes for the fault to rupture and the second is the length of time shaking is felt at any given point (e.g. when someone says "I felt it shake for 10 seconds" they are making a statement about the...
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)...
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...
It is relatively easy to acquire the necessary materials and build your own seismometer. The links here are to various sources with information on how to build a seismometer. They range from very simple and inexpensive to sophisticated and pricey. Model Seismograph - Classroom Demonstration Build your own Seismograph Station Build Your Own Seismograph Amateur Seismology Homebuilt Seismograph FAQ
A seismometer is the internal part of the seismograph, which may be a pendulum or a mass mounted on a spring; however, it is often used synonymously with "seismograph". Seismographs are instruments used to record the motion of the ground during an earthquake. They are installed in the ground throughout the world and operated as part of a seismographic network. The earliest "seismoscope" was...
The earliest seismoscope was invented by the Chinese philosopher Chang Heng in A.D. 132. This was a large urn on the outside of which were eight dragon heads facing the eight principal directions of the compass. Below each dragon head was a toad with its mouth opened toward the dragon. When an earthquake occurred, one or more of the eight dragon-mouths would release a ball into the open mouth of...
Plots showing Mauna Loa ground deformation and earthquake monitoring data between midnight August 1 and midnight August 3, 2022. The top panel shows ground tilt in microradians at station MOK, on the northwest side of Mauna Loa’s summit caldera. A histogram showing the number of located earthquakes that occurred per hour is shown in the middle panel.
Plots showing Mauna Loa ground deformation and earthquake monitoring data between midnight August 1 and midnight August 3, 2022. The top panel shows ground tilt in microradians at station MOK, on the northwest side of Mauna Loa’s summit caldera. A histogram showing the number of located earthquakes that occurred per hour is shown in the middle panel.
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.
Earthquakes at Mount Rainier from 2010 to 2019. As shown in the graphic, fluids from the magmatic system beneath the volcano rise through existing cracks and weaknesses in the crust. Along with rainwater and ice/snow melt, these fluids combine to create a hydrothermal system within the volcano.
Earthquakes at Mount Rainier from 2010 to 2019. As shown in the graphic, fluids from the magmatic system beneath the volcano rise through existing cracks and weaknesses in the crust. Along with rainwater and ice/snow melt, these fluids combine to create a hydrothermal system within the volcano.
Graphic shows the earthquake swarm from June-July, 2019, compared to previous swarms detected in March 2019, 2017, 2016, and in 2014. The activity is likely the result of small-scale underground movements of hydrothermal fluids or gas — a sign that Mount St. Helens remains an active volcano.
Graphic shows the earthquake swarm from June-July, 2019, compared to previous swarms detected in March 2019, 2017, 2016, and in 2014. The activity is likely the result of small-scale underground movements of hydrothermal fluids or gas — a sign that Mount St. Helens remains an active volcano.
Locations (Lat, Long, Depth) of January 17, 2010, earthquake swarm on Madison Plateau, Yellowstone National Park.
Locations (Lat, Long, Depth) of January 17, 2010, earthquake swarm on Madison Plateau, Yellowstone National Park.
