Why do so many earthquakes occur at a depth of 10km?
Ten kilometers is a "fixed depth." Sometimes data are too poor to compute a reliable depth for an earthquake. In such cases, the depth is assigned to be 10 km. Why that number? In many areas around the world, reliable depths tend to average 10 km or close to it. For example, if we made a histogram of the reliable depths in such an area, we'd expect to see a peak around 10 km. So if we don't know the depth, 10 km is a reasonable guess. The USGS used to use 33 km, but increased understanding indicates that 10 km is more likely.
Some areas, like subduction zones, are known to have many earthquakes much deeper than 10 km. In those areas, a deeper fixed depth would probably be appropriate. The most common reason for having to fix the depth is that the earthquake occurred too far from the nearest seismic station. A useful rule of thumb is that a reliable depth requires that the distance from the epicenter to the nearest station must be less than the depth of the earthquake.
Modern computational and theoretical advances can now produce reliable depths at greater distances from the nearest station, so the rule of thumb does not always apply. However, the rule of thumb does illustrate one conclusion: fixed depths are more common for shallow earthquakes than for deep ones.
Related
Why/When does the USGS update the magnitude of an earthquake? Why/When does the USGS update the magnitude of an earthquake?
The USGS often updates an earthquake's magnitude in the hours and sometimes days following the event. Updates occur as more data become available for analysis and more time-intensive analysis is performed. Additional updates are possible as part of the standard procedure of assembling a final earthquake catalog. There are physical and operational constraints on how quickly seismic data are...
How quickly is earthquake information posted to the USGS website and sent out via the Earthquake Notification Service (ENS) and other feeds? How quickly is earthquake information posted to the USGS website and sent out via the Earthquake Notification Service (ENS) and other feeds?
USGS earthquake information mechanisms are all triggered by the same system, so they all receive the information at the same time. The time it takes for the system to receive the information primarily depends on the size and location of the earthquake: An earthquake in California is processed and posted to the system in 2.5 minutes (on average). This is because our seismic network is very...
Where can I see current or past seismograms? Where can I see current or past seismograms?
The USGS Earthquake Hazards Program has helicorders (seismogram displays) available for several areas in the United States and the World. Our research partner IRIS (Incorporated Research Institutions for Seismology) has two applications, the Station Monitor and the Global Seismogram Viewer, for viewing seismograms. IRIS also supplies software that allows users to collect and view seismic data from...
Why do USGS earthquake magnitudes differ from those published by other agencies? Why do USGS earthquake magnitudes differ from those published by other agencies?
Magnitude estimates for a given earthquake can vary between reporting agencies due to differences in methodology, data availability, and inherent uncertainties in seismic data. Individual agencies use magnitude estimation procedures designed to meet the agency's specific needs and monitoring capabilities. Even for well-recorded events, differences in magnitude of 0.2 or 0.3 units are common and...
What is UTC, and why do you report earthquakes in UTC? What is UTC, and why do you report earthquakes in UTC?
UTC stands for Coordinated Universal Time, and for this purpose is the same as GMT (Greenwich Mean Time). Since the USGS and other seismic network agencies record earthquakes around the globe in all the various time zones, using a single standard time reference is best for record-keeping and exchange of data. The individual event pages with details about each earthquake use UTC for the reference...
Related
Why/When does the USGS update the magnitude of an earthquake? Why/When does the USGS update the magnitude of an earthquake?
The USGS often updates an earthquake's magnitude in the hours and sometimes days following the event. Updates occur as more data become available for analysis and more time-intensive analysis is performed. Additional updates are possible as part of the standard procedure of assembling a final earthquake catalog. There are physical and operational constraints on how quickly seismic data are...
How quickly is earthquake information posted to the USGS website and sent out via the Earthquake Notification Service (ENS) and other feeds? How quickly is earthquake information posted to the USGS website and sent out via the Earthquake Notification Service (ENS) and other feeds?
USGS earthquake information mechanisms are all triggered by the same system, so they all receive the information at the same time. The time it takes for the system to receive the information primarily depends on the size and location of the earthquake: An earthquake in California is processed and posted to the system in 2.5 minutes (on average). This is because our seismic network is very...
Where can I see current or past seismograms? Where can I see current or past seismograms?
The USGS Earthquake Hazards Program has helicorders (seismogram displays) available for several areas in the United States and the World. Our research partner IRIS (Incorporated Research Institutions for Seismology) has two applications, the Station Monitor and the Global Seismogram Viewer, for viewing seismograms. IRIS also supplies software that allows users to collect and view seismic data from...
Why do USGS earthquake magnitudes differ from those published by other agencies? Why do USGS earthquake magnitudes differ from those published by other agencies?
Magnitude estimates for a given earthquake can vary between reporting agencies due to differences in methodology, data availability, and inherent uncertainties in seismic data. Individual agencies use magnitude estimation procedures designed to meet the agency's specific needs and monitoring capabilities. Even for well-recorded events, differences in magnitude of 0.2 or 0.3 units are common and...
What is UTC, and why do you report earthquakes in UTC? What is UTC, and why do you report earthquakes in UTC?
UTC stands for Coordinated Universal Time, and for this purpose is the same as GMT (Greenwich Mean Time). Since the USGS and other seismic network agencies record earthquakes around the globe in all the various time zones, using a single standard time reference is best for record-keeping and exchange of data. The individual event pages with details about each earthquake use UTC for the reference...