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Input Dataset and Output Format

There is currently only one ANSS/CNSS earthquake catalog available for this catalog search form. At this time, the catalog only contains information about earthquake locations and magnitude and does not contain phase readings, amplitude observations, or mechanisms. We hope to address this in the future.

The earliest entries in the ANSS/CNSS catalog are in 1898. Many networks update their holdings daily. The catalog caveats page documents the current holdings.

There are currently 3 output formats available from the catalog search.

• Readable catalog format. This format is an easy-to-read table in a uniform format containing the basic event information, such as time, epicenter, depth, magnitude, # of stations, azimuthal gap, etc. This is the most readable output, and should be used for all preliminary searches.
• Readable 80-character format. This format is also easy-to-read, but is more abbreviated in the information provided.
• Raw catalog format. This will return the raw catalog entries for the selected entries from the specified input dataset.

Documentation on the output formats is available online. The source codes for the networks and agencies that contribute earthquake information are available as well.

Select earthquake parameters

The earthquake catalogs may be filtered using several different parameters including time, location (latitude and longitude), magnitude, and depth. Additional criteria are available.

• Date,Time parameters
  All time in the earthquake catalog is referenced to UTC. Date and time parameters can be specified in one of several formats:
  • yyyy/mm/dd,HH:MM:SS
  • yyyy.doy,HH:MM:SS.
  where:
  • yyyy = year (1898-present)
  • doy = day-of-year (1-366) >li>mm = month (1-12)
  • dd = day-of-month(1-31)
  • HH = hour (0-23)
  • MM = minute (0-59)
  • SS = second (0-59.9999)
  The date must be fully specified. The time is optional, and defaults to midnight if not specified. There cannot be any blanks between the date and time, or within the date,time string. The year MUST completely specified, eg 1999, not 99.

• Latitude and Longitude parameters
  Latitude and Longitude values can be specified in one of two formats:
  • decimal degrees, such as 39.50 for 39 and one-half degrees.
  • degrees and minutes, such as 39:30 for 39 degrees and 30 minutes.
  Latitude values can range from -90 to 90, and longitude values can range from -180 to 180. Please remember that:
  • Longitude for California is WEST, and therefore should be specified as NEGATIVE (eg -121.5 for 121.5 degrees West).
  • Since longitude is signed, a search between longitudes of -117 and -121 should be specified with a Min longitude = -121 and a Max longitude = -117.
  • No search area (neither a simple lat/lon box nor a polygonal region may cross the -180/180 degree longitude. If you wish to search a region that crosses this boundary, you must perform 2 distinct searches. For example, if you wish to search the 15 degree region between 175 degrees longitude and -170 degrees longitude, you must perform the search as 2 distinct request using:
    1. First search boundary:
       • Minimum Longitude: 170
       • Maximum Longitude: 180
    2. Second search boundary:
       • Minimum Longitude: -180
       • Maximum Longitude: -170

  The USGS GNIS Mapping Query Form can be used to find the latitude and longitude of a specific town or geographic feature.

• Additional search parameters
  Additional search parameters for selecting earthquakes may be specified by entering the appropriate keyword=value strings in the "Additional Search Parameters" box. Most search parameters are min/max parameters which allow you to provide minimum and/or maximum values for specific fields in the event catalogs. However, you may also select earthquakes within a specified annulus (or ring) around a location with the delta parameter, or specify a polygonal region to confine your earthquake search to a more complex region than a simple latitude/longitude box.

  Min/Max parameters

  Search parameters that have min and max values can be specified by the strings

  • minkeyword=value
  • maxkeyword=value
  where the strings min and max preceed the keyword. If you only specify one end of the range (either the min or the max value), the other end of the range will be determined appropriately. For example, to specify the that you want events where the closest station is between 1 and 20 km, you would specify
  • minclose=1 maxclose=20
  and to specify you want events where the closest station is <= 25 km from the epicenter, you would specify
  • maxclose=25
  There should be NO blanks in the parameter=value string. Multiple parameters may be entered on the same line if they are separated by one or more blanks.

  The following keywords can be used in min and max values parameter strings:

  • sta - number of stations used for solution (range: 0 to ...).
  • close - distance of closest station to epicenter (range: 0 to ...).
  • rms - root-mean-squared residual of solution (range: 0. to 1.).
  • gap - azimuthal gap (range: 0 to 360).

  Delta parameter

  You may search for all earthquakes that are within an annulus (ie between a minimum and maximum distance) from a location with the delta parameter.

  • delta=lat,lon,mindist,maxdist
  where lat,lon specify the latitude and longitude of the center of the circle, and mindist,maxdist specify the minimum distance and maximum distance in kilometers (km) of earthquakes from the specified location. Only earthquakes that are between mindist and maxdist kilometers from the specified location will be selected. There should be NO blanks in the delta=value string.

  Examples:

  • delta=38.5,-118.5,0,50
    specifies a circle (annulus with inner diameter of 0) of 50 km around the location (38,5,-118.5). The program will select only earthquakes that are located within this circle.
  • delta=38.5,-118.5,20,50 specifies an annulus (ring) of 20 to 50 km around the location (38,5,-118.5). The program will select only earthquakes that are located within this annulus.

    WARNING: The delta function will break if the circle centered at lat,lon with diameter of maxdist kilometers contains either of the earth's poles.

  Polygon parameter

  You may specify a polygonal search area with the polygon parameter.

  • polygon=lat_1,lon_1,lat_2,lon_2,,...,lat_N,lon_N
  where lat_i,lon_i specify the latitude and longitude of the i-th vertex of the polygon. You should ensure that the last point is identical to the first point in order to define a closed polygon. There should be NO blanks in the polygon=value string.

  Example:

  • polygon=37.4,-122.7,37.9,-122.75,37.9,-122.3,37.0,-122.0,37.4,-122.7
    defines a polygon that encloses that Bay Area Peninsula.

  The polygon must NOT cross the -180/180 degree longitude boundary, since the definition of the polygonal region becomes ambiguous.

Select output mechanism

By default, the output from the search will be returned to your browser in another document. Most browsers have the capability of directing a document directly to a local disk file instead of displaying it on the screen.

If you think that the search may generate more data than your brower can safely display, you should either set your browser to download documents directly to disk, so that the results of the search will be placed on your computer's disk, or you should specify that the output should be sent to an anonymous ftp file at the NCEDC.

If you send the output to anonymous ftp, you will be informed of the pathname and URL for the file so that you can retrieve it at your convenience. Please delete the file from the NCEDC when you are finished with it. The file will be automatically deleted in within several days if you do not delete it.

Line Limit

It is very easy to generate a lot of unwanted output by inadventently mis-typing any of the search parameters. For example, entering a minimum magnitude of 0.5 instead of 5.0 can signicantly alter the number of matches from a catalog search, and can easily generate megabytes of output from a phase retrieval request.

In order to protect yourself (and the NCEDC) from runaway searches, you should limit the number of lines that the search will generate before it is aborted. If you set this limit to a reasonable value on your desired request, it can help to prevent runaway searches that can result from mis-typed values.

You can disable the output line limit by deleting the value in the line limit field, or by entering a value of 0. Please use this setting with extreme caution.