Help using the catalog search
There is currently only one ANSS 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 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.
The earthquake catalogs may be filtered using several different parameters including time, location (latitude and longitude), magnitude, and depth. Additional criteria are available.
All time in the earthquake catalog is referenced to UTC. Date and time parameters can be specified in one of several formats:
- 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)
- 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.
- 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
- First search boundary:
- Minimum Longitude: 170
- Maximum Longitude: 180
- Second search boundary:
- Minimum Longitude: -180
- Maximum Longitude: -170
- First search boundary:
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.
Search parameters that have min and max values can be specified by the strings
- minclose=1 maxclose=20
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).
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.
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.
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.
You may specify a polygonal search area with the polygon parameter.
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.
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.
- 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.