Frequently Asked Questions

  1. What is USArray?
  2. Where is the data collected by USArray stored?
  3. Is there a movie that I can watch that shows the USArray deployment?
  4. What is the ANF?
  5. What are the responsibilities of the ANF?
  6. Why does the station map take so long to load?
  7. What do the column headings in the station table mean?
  8. Why are there several solutions for the same event, often with different magnitudes and locations?
  9. Operational information
  10. What criteria do you use to name a new station/site?
  11. How can I host a USArray station?
  12. What is SNOFLU?

There is an additional series of frequently asked questions and answers at the EarthScope USArray website.

What is USArray?

You can learn about the USArray component of the EarthScope experiment by clicking here.

Where is the data collected by USArray stored?

The data collected by USArray is stored at the Incorporated Research Institutions for Seismology (IRIS) Data Management Center (DMC).
Click here to learn more.

Is there a movie that I can watch that shows the USArray deployment?

High–resolution and iPhone formatted movies of both the rolling and cumulative station deployment can be viewed on the Monthly Deployment History page.

What is the ANF?

Click here for more information.

What are the responsibilities of the ANF?

The ANF is responsible for:

Why does the station map take so long to load?

The station map is created dynamically, communicating with the station database to ensure the most recent USArray station deployments are plotted. This is why there is a date-stamp at the base of the image in the legend noting how many stations were online at that precise time.

The station map should load in under 10 seconds if you are on a T1 connection, in under 30 seconds if you are using a 56K modem, but up to 120 seconds if you are using a 28K modem. Please be patient and wait for the image to load – there is a lot of information being processed to create the image.

What do the column headings in the station table mean?

The station table has six columns — Station ID, Station Name, Latitude, Longitude, Elevation and Ondate. The Station ID is a unique identifier to each respective station. The Station Name either describes the location of the station, or is a particular location. Latitude is in degrees (°) north, so a negative number means that the station is south of the equator. Longitude is in degrees (°) east, so a negative number means that the station is west of the Greenwich meridian in London, England (the location of zero degrees longitude). Elevation is the height above sea level in meters.

The Ondate is a number that is a combination of the year (four values) and the Julian Day (three values) and refers to the last time something was modified at that station (ie. a new sensor was installed, a different sample rate was implemented, etc.). Thus, an ondate of 2004100 does not mean that the station first started operating in 2004, only that a change in its setup occurred then: it could have been operational for 25 years prior to the reported “ondate”.

Why are there several solutions for the same event, often with different magnitudes and locations?

There are several reasons for different reporting bodies producing different locations and magnitudes for the same earthquake. The most fundamental cause is the location and number of seismic stations that recorded the earthquake. The magnitude and the location of a given earthquake is preferably determined using more than one seismic station. A suite of seismic stations distributed around the earthquake's epicenter and have a range of source/station distances can typically yield better location and magnitude estimates than a single station far away. However, other factors can also introduce additional deviations in the measurement such as differences in the recording capabilities of the seismic sensors, the seismic analyst making the measurement and variations in the geology and tectonics of the region. A rule of thumb used by some seismologists is that magnitude estimates can typically deviate by 0.5 magnitude units, and the mapped location of the earthquake (latitude, longitude) is often known in greater detail than the depth of the earthquake (distance from the Earth's surface to the earthquake's hypocenter).

A second variable is by what process the event is measured, and which scale is used. There are four different measurement scales — surface wave magnitude (Ms), body wave magnitude (mb), moment magnitude (Mw), and local magnitude (Ml).

Learn more about measuring earthquake magnitudes.

Operational Information

What criteria do you use to name a new station/site?

A Transportable Array station code is 4 characters long. The first three characters of a new station's station code are based on its geographic location. The last (fourth) character identifies the sequence of stations installed at this grid point. Often the first planned site had complications that prevented its inclusion, so instead of "A", you will see "B" or "C", and so on. Normally only one station would lie in a grid point but if a station must be relocated the scheme must easily support this possibility. A fifth character is possible for SEED station codes, however this character is undefined for the present time.

The geographic based naming convention is based on a grid system with geographic placement amongst the rows and columns defining a different part of the station code. There are rows of stations A, B, C, etc. starting at the Canadian border and incrementing an idealized every 75 km or so until reaching the border with Mexico and columns starting at "01" at the westernmost point in the US deployment plan and incrementing by one as you move approximately every 75 km to the east. More than 26 rows are needed to accomplish this gridding so after "Z" comes a station starting with "1". Less than 99 columns (64 in total) are needed to accomplish this gridding, so the 2nd and 3rd characters will always be numeric. Thus the station code takes its first character based on its latitude and the numeric second and third characters are based on its longitude. Due to the obvious difficulties with siting, the idealized 75km grid spacing is adjusted to fit the conditions in the area.

Let's take as an example station A12A. The first "A" tells us that this is a 'northern' site near the border with Canada. The "12" tells us that it is 12 grid points in from the westernmost point in the deployment grid. Very approximately that is 12*75 km from the westernmost point. The final "A" tells us this was the first location for a station at this grid point. This ends up being a site in Montana.

Prior to final installation and certification, site codes include a dash followed by a number that identifies the classification of the site.

When one of the potential sites is permitted it is referred to by the station code A12A. The SEED station code is the station code, the Network code for USArray Transportable Array is TA. You may seed a station code written as TA.A12A or TA_A12A.

To view a table of all the planned station deployments please visit the EarthScope USArray deployment website.

How can I host a USArray station?

If you are interested in hosting a seismic station on your property please visit the IRIS webpage dedicated to this. You can also download a PDF information brochure. Thank you for your interest.

What is SNOFLU?

SNOFLU is an acronym for Sudden Noise Onset Fixed by Lock/Unlock. It is a known sensor issue with certain datalogger types, when for no apparent reason the station channel(s) start to get noisy. This is fixed by a physical mass position lock and unlock process on the sensor.