The SCSN catalog spans over 90 years, a period that has seen significant changes in the way we measure, analyze and distribute earthquake information; a process that will continue to evolve as the science and technology advances. Below is a summary of the catalog’s history, and some of the issues arising from the changes during its collation.
For researchers seeking specific review status of the catalog at different points in time, the SCEDC provides a helpful resource, the SCEDC Catalog Status Files. This special catalog tool provides information on the number of catalog events that have been reviewed, or are awaiting review, by our team of seismic analysts, giving context to the review status of the catalog.
1932 – 1976: Early Data
- The events from the 1932-1976 era of seismic data are derived from the original hand-written phase cards which originally came from hand measurements on drum records. The data were keyed into electronic CUSP (Caltech-USGS Seismic Processing) format on a VAX system from the phase card solutions by a data entry contractor. Each event was later reviewed and located by a Caltech seismic analyst. Some events were located with HypoInverse, some with “grope” (a CUSP location program) and some with simulps (a 3D location program using S and P times) The data were then imported into the SCEDC database, to make phase and epicenter data available for direct retrieval by users.
1932 – 1971
- Minor checking of the events in this era is still required. Locations and magnitudes may change somewhat, but not significantly.
- Some events that were not included in the phase cards (for example, aftershocks that were just listed, without “their own” readings) are currently missing, but we plan to add these events.
- Magnitudes for this time period use the most recent known ML calibration and attenuation function.
- Note that this time period contains some small events that were excluded, probably with good reason, from the canonical catalog. (Hileman et al. “Seismicity of the Southern California Region”).
1972 – 1974
- These events were located from a combination of drum readings and develocorder readings.
- There are missing events during this time period because we cannot find phase information for very small events (about 80% of them “1.7”) in “USGS areas” that were listed in the old catalog. If we cannot recover the phases, we will insert the events with only their catalog information but without the supporting phase and amplitude data to verify the locations and magnitudes.
1975 – 1976
- Locations are unlikely to change, but magnitudes may change slightly when recomputed using the newest calibration.
1977 – 1980: The CEDAR Era
- A problematic four-year span of CEDAR (Caltech Earthquake Detection and Recording) data from 1977-1980 is currently not available to web searching, but has been converted and is being processed to include magnitude information. The waveform data that was available was read from tape and loaded onto the CUSP VAX system and converted to mSEED format.
- Some of the problems we need to resolve before we can make this era of data available are:
- Missing events, due to unreadable 9-track archive tapes. Most of these events can be added to the database from the ASCII catalog and “PINK” cards with matched phase data from an archive of 9 track tapes (sometimes called the Corbett tapes); however, these events will not have waveforms.
- Events with corrupted waveforms. These unreadable waveforms are due to corrupted archive tapes. There is not much we can do with these waveforms, except verify that the phase data support the locations.
- Times and phase-picks need to be checked for events that have readable waveforms. There is a discrepancy between the two WWVB time code channels on some events, so we need to verify that the correct one is the one reflected in the phase pick times. This may be an extremely difficult task, complicated by the fact that some of the original time information was lost in the two translations.
- There are currently no magnitudes for this era of data. We need to enter Wood-Anderson amplitudes (to get MLs) for those events that have them on the phase cards. Then we need to either enter the previously computed Mcs, or (preferably) recalibrate and recompute Mc or Md for the other events.
- The waveforms during this era often have sporadic noise spikes. The waveforms are useful for visual picking, but may present problems for numerical processing.
1980
- 1980 is currently not searchable. These events happened during a time period when a Real Time data acquisition system was working, but the post-processing system (CUSP) was still under development. The untimed events constitute a “backlog” which was never finished due to data translation problems.
- At least some of these events need to be picked and located.
- We need to enter Wood-Anderson amplitudes (to get MLs) for those events that have them. Then we need to either enter the previously computed Mcs, or recalibrate and recompute Mc or Md for the other events.
- We expect to find time problems and events missing caused by unreadable archive tapes.
- Events that are completely missing from the converted CEDAR system will need to have their phase data and parametric data entered in the database from the ASCII catalog and “PINK” cards with matched phase data from the Corbett tapes; however, these events will not have supporting waveforms.
1981 – 1999: The CUSP Era
- The parametric data from 1981 to present have been loaded into the database system and the waveforms for that time period have been converted to mSEED format and are accessible through the STP interface. Quality control verification of 1981-2000 historic parametric and waveform data has progressed using a detailed reverse-chronological examination and verification of magnitudes.
- There are a number of events that have zero magnitudes during this era. We are working toward getting magnitudes for these events:
|
Year |
# Zero Mag Events |
|
1975 |
577 |
|
1976 |
2086 |
|
1981 |
5210 |
|
1982 |
3574 |
|
1983 |
4819 |
|
1984 |
1271 |
|
1985 |
1336 |
|
1986 |
1376 |
|
1987 |
1040 |
|
1988 |
5026 |
|
1989 |
815 |
|
1990 |
966 |
|
1991 |
5797 |
|
1992 |
796 |
|
1993 |
501 |
|
1994 |
541 |
|
1995 |
626 |
|
1996 |
654 |
|
1997 |
1441 |
|
1998 |
1679 |
|
1999 |
2742 |
1981 – 1982
- The timing and locations for these data are good. We need to insert Wood-Anderson amps to get ML.s, and verify or insert magnitudes for other events.
- There are still missing events for these years that were not found on the CUSP system, but were listed in the catalog.
1983
- Most of the data is good, but there may still be some .backlog. events that still need to be picked.
- Wood-Anderson amplitudes may need to be inserted. Magnitudes may need to be verified or inserted.
1984 – 1999
- Good data. We expect that the catalog is complete and all but a few events have reasonable magnitudes.
- We are aware of some location problems which require a .starting location. feature in Jiggle to fix.
- We are aware that the most of the ML.s were computed with an old calibration and attenuation function.
- We now have the capability to check all the magnitudes and improve some of the locations during the intense parts of aftershock sequences. We will do this as we have time.
2000 – present: The TriNet – SCSN/CISN Era
- The data archived by the Data Center are now available within a few minutes of the origin time of the earthquake. All the data produced by the real-time monitoring network are placed immediately in the SCEDC Oracle database system, where they are subsequently revised by further analysis. A time delay of a few days used to be the standard for new data to be available at the SCEDC; however, since the inception of the SCSN/CISN (formerly TriNet) system and with changes in the daily operations and daily archiving of the Data Center, new earthquake data are available to the community in near real-time.
2000
- During 2000, although CUSP was the authoritative system, the TriNet system was running and would take over as the primary system in 2001. The outcome of both systems running concurrently resulted in four possible types of events. The SCEDC has taken the following steps with each of these event types:
- Identical Hypocenters – Each system generates a solution, resulting in two event IDs for the same event.
Solution: took the TriNet event and added CUSP data to create a superset of data for the event. The side effect of this solution is that the CUSP event id for this event no longer exists in the catalog. - CUSP, but not TriNet – An event exists only in the CUSP system, but not on the TriNet system.
Solution: relaxed hypocenter constraints slightly to try to match to a TriNet event. If a match, we proceeded as in step 1; else, the event was converted and loaded into the database. - TriNet, but not CUSP – An event exists only in the TriNet system, but not on the CUSP system.
Solution: relaxed hypocenter constraints slightly to try to match to a CUSP event. If a match, we proceeded as in step 1; else, the event is already in the TriNet database, so it continues to exist. - Bogus Events – Early in 2000, TriNet’s triggering algorithm generated a high number of noise events. These were investigated and if they were not true network triggers, they were deleted.
- Identical Hypocenters – Each system generates a solution, resulting in two event IDs for the same event.
- The net effect is that we may have some duplicate events for the year 2000. We are gradually removing these by individual inspection.
2001-2003
- There may be minor problems with the synthetic Wood-Anderson amplitudes for the time period 2001 through mid-2003. We will ultimately want to recompute the magnitudes to have a consistent catalog.
2008
- On January 1, 2008, the Southern California Seismic Network began using an updated method of measuring local magnitude (Ml). To ensure consistency in the Southern California Earthquake Catalog, we will begin recalibrating the Ml magnitudes for events between January 1, 1992 to January 1 2008 using this same method. The processing will be starting with events in December 2007, and going back one month at a time. These recalibrated magnitudes will be seen in the catalog search page. Processing begins May 1, 2009. If you wish to view historical data with the legacy magnitudes, text files of the catalogs can be found here: http://service.scedc.caltech.edu/ftp/catalogs/SCSN_pre2008/ Information on the revised Ml calculation is given the publication: R. A. Uhrhammer, M. Hellweg, K. Hutton, P. Lombard, A. W. Walters, E. Hauksson and D. Oppenheimer; California Integrated Seismic Network (CISN) Local Magnitude Determination in California (to be submitted) to BSSA, 2009
2010
- Starting Jan 1, 2010, SCEDC archives high sample strong motion channels continuously
- Data sets for M7.2 Sierra El Mayor Cucapah Earthquake
- GPS displacement waveforms from California Real Time Network for M7.2 Sierra El Mayor Cucapah Earthquake
2011
- American Recovery and Reinvestment Act (ARRA) improves the data quality of the SCEDC archive.
- New waveform relocated earthquake catalog available.
- New focal mechanism catalog available.
2012
- In response to the user community, we are now putting our catalog files, both SCSN and SCEDC format in version control at GitHub. The repository is https://github.com/SCEDC/SCEDC-catalogs
- SCEDC is now archiving real time GPS displacement waveforms. 7/02/2012
- Strong motion waveforms from California Geological Survey now available in the archive. 12/06/12
2013
- The Southern California Seismic Network (SCSN) made changes to its real time event detection software which should improve its accuracy in detecting events as well as determining accurate locations and magnitude. The change was to add the no_S_on_Z parameter to binder.
- Due to a recent confluence of moderately high seismicity, more stations to process, and level staffing, we have been forced to make some changes in the earthquake catalog processing. These changes went into effect at the time of the March 2013 Anza sequence. Prior to April 2013, we made every reasonable effort to place every impulsive pick at the correct time, and some emergent picks as well. This procedure improved the locations, but also caused long delays in getting large sequences processed.
- Each earthquake must still be reviewed by an analyst, to make sure that the location and magnitude are within reasonable accuracy (which depends on the geographic location), and quarry blasts are appropriately marked.
- More reliance on an automatic picker that is tailored to the post-processing environment.
- Nearest 5 to 10 stations are accurately timed.
- Since more stations means denser coverage, most picks beyond 100 km distance not included (again, this depends on the geographic area).
- Earthquakes with 2.5 or larger magnitude get the same attention as before.
- Because the automatic picker may not choose the correct wave, there may be a degradation in the focal mechanisms for small quakes. New software probably offsets this problem, by also incorporating S amplitudes into the solution.
- If an earthquake passes through this process, it has an “I” or “intermediate” processing state, which flags the event for further review at a later time. If activity is low, or there is some reason it is efficient or necessary to completely time an earthquake, it moves to an “F” or “finalized” processing state. This means analysis has been completed for this event.
- The Southern California Seismic Network (SCSN) made changes to its real time event detection software which should improve its accuracy in detecting events as well as determining accurate locations and magnitude. A detailed list is as follows:
- new binder_ew binary Version <1.0.11 2013.03.22>
- binder_ew, eqproc and eqassemble using PICK_RING (instead of FILTERPICK_RING)
- changed the grid weight from 0,0 to 2,1 for picks with quality 2 and 3
- no_P_on_Horiz
- Channel number Maps:
- ChannelNumberMapByNet NEZ PB
- ChannelNumberMapByNet ZNE CI
- ChannelNumberMapByNet ZNE CE
- ChannelNumberMap ZNE
- rstack 60.0
- new trimag binary – VERSION: TriMag2 v0.2.8, 2011-05-06
- parameters for trimag:
- MinCutoffDist 20.0
- MaxCutoffDist 200.0
- StepCutoffDist 20.0
- DefaultCutoffDist 150.0
- UseCITwindows 0
- PostSMult 1.0
- PostBuffer 1.0
2014
- New waveform relocated earthquake catalog available.(09/05/2014)
- New focal mechanism catalog available.(09/05/2014)
2015
- On September 22, 2015, the SCEDC earthquake catalogs began reporting event depths relative to the WGS84 reference ellipsoid. Older versions of the catalog with the model depth datum will be available on the SCEDC repository on GitHub. Relative to the reference ellipsoid, shallow earthquakes may now have negative depths as ground elevations in California range approximately from +0.085 km (Death Valley, below sea level) to -4.421 km (Mount Whitney). The catalog search minimum depth will therefore be set to a default value of -5 km.
- The SCEDC earthquake catalog formats “SCEDC” and “SCSN/Catread” had the following format changes:
- A new column: geographic type is added.
- Changes in values for Event Type. Events previously with values “le”,”re”,”ts” will now have an event type of “eq” and geographic types of “l”, “r”, and “t” respectively.
- Due to reduced funding and personnel, the analysis practices (or post processing) of the earthquake catalog were revised in order to continue handling, in a timely manner, the full, continuous, seismic workload. While aiming to preserve as much data quality as possible, starting as of January 1st, 2015 every detected event will no longer go through the obligatory and thorough hand-timing by an analyst. While every event is still reviewed by a seismologist, a significant portion goes through only a visual inspection, before it is finalized in the catalog. All events M2.5 or greater or those failing the initial summary inspection, will undergo full, manual analysis. Under the new practices, there will be events processed only (and completely) by the automated system. To ensure quality, all events with automated solutions that have an RMS of 0.4 or greater, or with anomalous depths or magnitudes will be fully analyzed. There is no identification in the catalog for which events have been manually timed and which have been only automatically timed and inspected. We will be reviewing the catalog to assess if there is any impact of this change in procedure. We thank you for your understanding.
2016
- Starting at the end of December 2015, SCSN began calculating an additional magnitude type, labelled Mlr, which is a revised local, or Richter, magnitude (Ml). Mlr magnitudes are only calculated for events with Ml between 3.0 and 6.0, and are obtained by applying a linear adjustment to the Ml value. The adjustment is designed to bring initial magnitude values derived from Ml into closer agreement with moment magnitude (Mw) values (which take somewhat longer to calculate), because Mw is expected to be the preferred magnitude type for events above magnitude 3.5.
- For most areas in southern California, Ml is systematically larger than Mw for magnitudes greater than 3.5, consequently the Mlr adjustment is a reduction of the Ml value of up to 0.5 unit (larger adjustment for larger events). Mlr is calculated using the following formula:
- Mlr = Ml * 0.853 + 0.40125
- For the majority of earthquakes, Ml will be the preferred magnitude for events smaller than 3.5 and Mw preferred for events greater than 3.5. Mlr may be the first reported magnitude for events larger than 3.5 and could be the preferred catalog magnitude if an Mw cannot be obtained. In general, catalog searches using the usual STP and web tools will not return an event’s Mlr value unless it is the preferred magnitude.
- For most areas in southern California, Ml is systematically larger than Mw for magnitudes greater than 3.5, consequently the Mlr adjustment is a reduction of the Ml value of up to 0.5 unit (larger adjustment for larger events). Mlr is calculated using the following formula:
- New waveform relocated earthquake and focal mechanism catalogs available (01/05/2016)
