NCSS Catalog Search Documentation

Select earthquake catalog

There are currently four earthquake catalogs available for the online search.

  • NCSN catalog, from 1967 to the present.
    Earthquakes located by the NCSN. There are also phase readings available for all events.
  • UCB catalog, from 1910 to the present.
    Earthquakes located by the UC Berkeley Seismological Laboratory. There are phase readings available for events starting in 1984.
  • NCSN Fault Plane Solutions, from 1967 to the present.
    This catalog contains a listing of the fault plane soutions for significant earthquakes, as determined by the first motion.
  • Double-Difference Catalog (1984-Present)
    Please see the NCEDC news entry on Double-Difference for background information on this format.

This part of the catalog search was recently revised to simplify the relationships between the input catalogs and the output formats. Here is a brief summary of the output formats:

  • 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. This is the same for all the catalogs.
  • Hypoinverse catalog format
    The NCSN catalog is stored in Hypoinverse or HYP2000 format, consisting of a single line per event.
  • Hypoinverse catalog and phase format
    The NCSN catalog and phase data are stored in a "shadow" format file, which consists of a summary line with location, and additional lines including phase lines for individual stations.
    Hypoinverse Shadow file format description
    Full Hypoinverse documentation
  • FPFIT format
    The NCSN fault plane solutions are Y2K HYPO71 summary cards, augmented with the fault-plane solution parameters.
  • UCB raw catalog format
    The UCB raw catalog format is an internal format, consisting of a single line per event.
  • UCB raw catalog and phase format
    The UCB raw catalog and phase format is an internal format, consisting of multiple lines per event.

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.
  • yyyy = year (1900-present)
  • doy = day-of-year (1-366)
  • 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.

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 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.


  • 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.


  • 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.

Select output mechanism

By default, the output from the search will be returned to your browser in another document. If you think that the search may generate more data than your brower can safely display, you can specify that the output should be sent to a file, available to download via http, at the NCEDC. The file will be automatically deleted within several days.

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.

Catalog Search FAQ

How can I get a list of earthquakes near my house (business, or other point of interest)?

The first step is to determine the latitude and longitude of your point of interest. Google Maps is a great resource for this. Once you have the coordinates, decide whether the northern California or the global catalog is more appropriate for your search. Once you have selected the catalog, use the delta feature of "additional search parameters" in the form to specify your point of interest.

For example, the coordinates of UC Berkeley in Berkeley, CA, are 37.8735, -122.2609. To obtain a list of earthquakes within 2 km of these coordinates, enter


This will return all events within a 2 km radius circle of the specified coordinates. When this search is run on the NCSN catalog for the year 2001 for all magnitudes, it returns 1 earthquake:

          2001/01/30 10:35:34.36  37.8785 -122.2473   9.29  1.05 coda

If your search does not return any earthquakes, consider enlarging the radius of your circle (remember, the circle radius is specified in kilometers, not miles!). The catalog search requires that West longitudes are specified with negative numbers.

I can't find an earthquake that I know occurred at a particular time. Why not?

In order to prevent confusion with the myriad of time zones around the world, seismologists use a single standard of time for reporting on earthquakes. Universal Time (UTC) is the agreed standard for earthquake reporting and is also known at Greenwich Mean Time (GMT) or Zulu time (Z). Universal Time is based on a 24-hour clock. Although useful - and necessary - to coordinate seismological observations around the world, the use of UTC can be confusing. For northern California, the classic example is the 1989 Loma Prieta earthquake, which occurred on Oct 17 17:04 local time and Oct 18 00:00 UTC.

Can I make a map of the earthquakes from the search?

Unfortunately, we do not currently support a tool for generating maps of the earthquakes produced from the catalog searchs.

Can I search across the -180/180 meridian?

The default "box" search over latitude and longitude does not support searchs across the -180/180 meridian. Neither does the polygon search option. This is due to the complications of determining whether an earthquake is inside or outside the polygon for searchs spanning the meridian. To do this type of search, you must break your request into two separate searchs.