Editing Seismogram (section)

==Recording==

Prior to the availability of digital processing of seismic data in the late 1970s, the records were done in a few different forms on different types of media.

A '''Helicorder''' drum is a device used to record data into photographic paper or in the form of paper and ink. A piece of paper is wrapped around a rotating drum of the helicorder which receives the seismic signal from a seismometer. For each predefined interval of data, the helicorder will plot the seismic data in one line before moving to the next line at the next interval. The paper must be changed after the helicorder writes on the last line of the paper. In the model that use ink, regular maintenance of the pen must be done for accurate recording.<ref>{{cite web|title=How to Read Helicorder Records|url=http://www.mgs.md.gov/seismic/help.shtml|publisher=Maryland Geological Survey|accessdate=4 July 2014}}</ref>

A '''Develocorder''' is a machine that records multi-channel seismic data into a [[16 mm film]]. The machine was developed by Teledyne Geotech during the mid-1960s.<ref name=ibm>{{cite report |last1=O'Neil |first1=W. |last2=Medberry |first2=A.H. |last3=Sokolowski |first3=T.J. |date=October 1990 |title=NOAA Technical Memorandum NWS AR-41: Concurrent Seismic Data Acquisition and Processing Using a Single IBM PS/2 Computer |url=http://docs.lib.noaa.gov/noaa_documents/NWS/TM_NWS_AR/TM_NWS_AR_41.pdf |accessdate=4 July 2014}}</ref> It can automatically plot seismograms from 18 seismic signal sources and 3 time signals on a continuous reel of film. The signals from seismometers are processed by 15.5&nbsp;Hz recording [[galvanometer]]s<ref>{{cite report |last1=Eaton |first1=J. P. |date=18 April 1993 |title=Review of Procedures for Calculating USGS Short-Period Seismograph system Response (Open-File Report 93-295) |publisher=United States Geological Survey |page=16 |url=http://pubs.usgs.gov/of/1993/0295/report.pdf |accessdate=4 July 2014}}</ref> which record the seismograms to a reel of {{convert|200|ft}} of film at the speeds between {{convert|3|and|20|cm|in}} per minute. The machine has self-contained circulating chemicals that are used to automatically develop the film.<ref>{{cite journal |date=1960 |title=Geotechnical Corp. Auto-Processing Film Recorder-Viewver |journal=Photographic Science and Engineering |publisher=Society of Photographic Scientists and Engineers |volume=4–5 |page=365}}</ref> However, the machine takes at least ten minutes from the time of recording to the time that the film can be viewed.<ref name=ibm/>

<gallery>
File:Develocorders Film Reel Container.jpg|A container that stores a Develocorder film reel
File:Develocorder Film.jpg|A Develocorder film reel
File:Viewing of Develocorder Film.jpg|Viewing of a Develocorder film
</gallery>

After the digital processing had been used, the archives of the seismograms were recorded on magnetic tapes. The data from the magnetic tapes can then be read back to reconstruct the original waveforms. Due to the deterioration of older magnetic tape medias, large number of waveforms from the archives in the early digital recording days are not recoverable.<ref>{{cite web |last1=Hutton |first1=Kate |last2=Yu |first2=Ellen |title=NEWS FLASH!! SCSN Earthquake Catalog Completed!! |publisher=Seismological Laboratory, Caltech |url=http://www.data.scec.org/about/scsncatalog.pdf |accessdate=4 July 2014 |url-status=dead |archiveurl=https://web.archive.org/web/20140714225025/http://www.data.scec.org/about/scsncatalog.pdf |archivedate=14 July 2014}}</ref> Today, many other forms are used to digitally record the seismograms into digital medias.<ref name=Bolt/>