The Preliminary Determination of Epicenters (PDE) Bulletin

The NEIC global earthquake bulletin is called the Preliminary Determination of Epicenters or PDE. We use the word "Preliminary" for our final bulletin because the Bulletin of the International Seismological Centre is considered to be the final global archive of parametric earthquake data (phase pick times and amplitudes).

PDE bulletin goes through three stages of review. To get data for the entire PDE bulletin, files for all three review stages must be down loaded. There are no duplicate earthquake solutions in the files for the different stages of review. When an earthquake moves from one review state to the next the "old" solution is deleted.

The daily PDE
Sometimes referred to as the Quick Epicenters Determinations (QED) or PDE-Q. Data files for this stage of review encompass approximately the last six weeks of earthquakes and are updated daily. Earthquakes can be added or modified anytime during these six weeks.
The weekly PDE
In on-line catalogs, events at this stage of review are identified as PDE-W. Data files for this stage of review span the time period between the most recent monthly PDE and the oldest published quake in the daily PDE (generally, approximately six weeks). There are 52 files per year, with the final PDE containing the remaining 1 or 2 days at the end of the year. New files are added on a weekly basis once final review of that time period is completed. Once the weekly PDE is posted, solutions for that time period are deleted from the daily (QED) files. Data in the weekly PDE files are not modified but are deleted when the earthquakes are published in the monthly PDE. Only minor changes are made to these data in the next and final stage of review (monthly PDE). Changes are generally only to the comments describing macro seismic effects and felt reports.
The monthly PDE
Officially named the PDE Monthly Listing, but shown in on-line catalogs as simply PDE. Digital data files containing pick and amplitude measurements for this stage of review span from 1990 to the oldest earthquake in the weekly PDE and are posted in one-month increments once final review for that time period is completed. Once the monthly PDE files are posted, the corresponding weekly PDE files for that time period are removed from the FTP site, because they have been completely replaced by the information in the monthly PDE. In general, only minor changes are made to the solutions in this stage of review, but it is possible that new events are added, old events modified and occasionally some old events from the weekly PDE may be removed. Hypocenter data is available on line from 1973. Previous to this time, bulletins are available in printed archives. Macroseismic comments and additional information about geological effects for significant earthquakes may be modified on the USGS Earthquake Hazards Program website at any time after the monthly PDE has been finalized, but in general those changes will not be made in the files on the FTP site.

File formats

PDE data is distributed in several formats and the file names in the ftp directories echo the format type of the file.

mchedr (machine readable Earthquake Data Report) - contains hypocenter parameters, macro-seismic observations, and phase and amplitude data. Full description of mchedr format.
ehdf (extended Hypocenter Data File) - contains only hypocenter data and flags for macroseismic and geological effects, one event per line. Full description of ehdf format.
isf (IASPEI Seismic Format) - files are created to share data with the International Seismological Centre but are used at other data centers and contain hypocenter parameters, macro-seismic observations, and phase and amplitude data. ISF format was approved by the International Association of Seismology and Physics of the EarthÕs Interior (IASPEI), and is an extension of the data format created by the International Data Center of the Comprehensive Test Ban Treaty Organization (IDC/CTBTO). ISF files are available only for final monthly data. Description of isf format (PDF).
manuscript - format is a more human readable listing of only hypocenter data with comments containing moment tensor information and observations of earthquake effects such as damage or deaths.

Obtaining PDE via FTP

daily PDE files:
weekly PDE files:

For all weekly files, WW is the two-digit week of the year and YYYY is the year. Week 52 contains all the remaining days of the year (generally 8 days, but 9 days in leap years).

monthly PDE files:

For all monthly formats, MM is the two-digit month of the year and YYYY is the year. The ehdf format files in the form ehdfYYYY.dat contain the data for the entire year and ehdfYYYYMM.dat files contain the same data split into months. The mchedr and isf format files are unix compressed to speed transfer.