Frequently Asked Questions

What is USArray?

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

Where is the Transportable Array USArray data collected by the ANF stored?

The Transportable Array seismic, infrasound and weather data collected at the ANF for the USArray project is stored at the Incorporated Research Institutions for Seismology (IRIS) Data Management Center (DMC).
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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?

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What are the responsibilities of the ANF?

The ANF is responsible for:

What do the column headings in the station table mean?

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The station table has six columns — ID, VNET, Location, Start Deployment, Data Latency, Last Day Performance. The ID is a unique identifier to each respective station. A VNET is a "Virtual Network Definition identifier that allows individually operated seismic networks to be grouped together for a single project. Location either describes the town, state, country of the station and can include a placed identifier instead of or in addition to the town/state/territory. The Start Deployment is when that station was added to the project. For most TA stations, this is the installation time of the station, but for contributing networks, this most often post-dates the installation date. Data Latency reflects the last time we saw current/real-time data from a station. Last Day Performance indicates data completeness fot that station calculated off of the BHZ channel of seismic data. Some stations do not return BHZ data and thus no performance metric is calculated.

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 multitudes of different measurement scales but common ones you may see reported are: 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.

A similar pattern of station naming was used when the array moved to Alaska. However, the fourth character was chosen to be "K" for the first instanace of a site within Alaska and "L" for susbsequent sites at that grid point. Stations in Canada used "M" or N" for their fourth character.

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. This was an occassional problem for stations deployed in the Lower48 and is not an issue for the posthole deployments in Alaska.

  Last updated: December 01 2020 20:34:27 (UTC).