Overview

Initially, RT AQMS automatically generates an event catalog with origin and magnitude information. RT AQMS uses the Earthworm software to automatically detect, locate, and characterize individual earthquake events in real-time. However, these automatic event origins are sometimes incorrect or need refinement. Therefore human analysts improve the automatic event solutions to generate a high-quality earthquake catalog.

At the SCSN, the Duty Review Page (DRP) and Trigger Review Page (TRP) tool are used as a first pass on the automatic event catalog. Based on visual inspection of the event waveforms, the analyst can either accept the event as an earthquake, or cancel the event if it does not look like an earthquake signal. Other RSNs may not have a DRP or TRP, so all human post-processing would be done through Jiggle.

After the first pass is complete, Jiggle is then used for more careful analysis of the earthquakes: picking phase arrival times, recomputing location, and recomputing magnitude. Jiggle is used to save and finalize an improved earthquake solution to the database, delete a non-earthquake event from the database, or create a new event in the database for an earthquake that was not detected automatically by RT AQMS.

Figure

There are two different types of events (as shown by ETYPE in screenshot above) in the automatically generated catalog from RT AQMS (all pink rows in screenshot above with ST set to A): earthquake and trigger, which have gone through separate processing paths in Earthworm.

  • At the SCSN, the DRP shows earthquake events that have passed through the Earthworm binder algorithm. These events have a location and magnitude associated with them. After viewing the waveforms, the analyst takes one of the following actions within DRP:

    • Accept event as an earthquake, which marks the event as human-reviewed. However, the event solution still needs to be reviewed, refined, and finalized within Jiggle.
    • Cancel event if it is not an earthquake, then delete event from catalog within Jiggle. This action is taken if RT AQMS has falsely detected a noise signal. Occasionally, an earthquake event may be canceled if the solution is really bad, then its solution recomputed within Jiggle.
    • Finalize event only if it is small (M < 1.95) and well-located (RMS < 0.23 seconds, this is the residual arrival time error). These usually have SRC set to "hypomag" in the final catalog.
    • Delete event is generally not done in the DRP; it is preferred practice to delete events within Jiggle.
  • At the SCSN, the TRP shows trigger events that went through the Earthworm subnet trigger algorithm, consisting of the carlstatrig and carlsubtrig modules, instead of binder. Triggers have an associated time, but no location or magnitude. After viewing the waveforms, the analyst takes one of the following actions within TRP:

    • Accept trigger if the waveforms look like it is an earthquake. The waveforms can be loaded into Jiggle. The analyst can then pick phases, locate the event, compute magnitude, then save and finalize the event as an earthquake in the standard procedure.
    • Delete trigger if the waveforms look like noise. This step deletes the trigger from the database forever, so that it never appears in Jiggle.

At the SCSN, the vast majority of events in the final catalog are local earthquakes, although a few events are regional or teleseismic earthquakes from farther away. Occasionally there are human-generated events such as quarry blasts, or even more unusual events. The final catalog of earthquakes in southern California is available to the public at the SCEDC website: http://scedc.caltech.edu/eq-catalogs.

Understanding Waveforms at SCSN.org - This website contains examples of waveforms from the different types of events listed below.

TODO: Link to SCSN wiki examples

Earthquake (Local)

Most earthquakes recorded by the SCSN are small local earthquakes that occur within the boundaries of the seismic network. The screenshot below shows waveforms from a typical local earthquake in the SCSN, with a distinctive P-wave and larger S-wave only a few seconds apart, detected at different times across many seismic stations in the network.

Figure

Most local earthquakes start out as events that were automatically detected and associated with the Earthworm binder algorithm within RT AQMS. Binder is optimized to detect events in denser areas of the seismic network.

  • These events have their origin event type (ETYPE) set to "earthquake", and their origin subsource (SRC) set to "RT" followed by a number.
  • These events have an initial location and magnitude associated with them, since the RT system has used HYPOINVERSE to compute the location and trimag to compute the magnitude.
  • Small events with M < 2.8 go through a second pass of automatic RT processing: hypomag applies aggressive filters to re-pick phases, re-locate the event, and re-compute their magnitudes. These events have SRC set to "hypomag" in the catalog.

At the SCSN, "earthquake" events that passed through binder end up in the DRP, where the analyst takes a first pass at post-processing by visually inspecting the event waveforms:

  • If the event is not an earthquake (for example, if the waveforms look like noise, as the result of a false detection by RT AQMS), the analyst should cancel the event in DRP, which leaves the event in the catalog but sends out a cancel alarm message. About 50% of events from the RT AQMS system in SCSN are canceled. All canceled events must be reviewed in Jiggle, where they can be deleted from the catalog.
    • Occasionally, an event that is an earthquake, but has a really bad location, may be canceled in DRP, so that alarm messages are sent to external websites to cancel the event. Jiggle can then be used to recompute its solution from the waveforms.
  • If the event is an earthquake, but it is small (M < 1.95) and well-located (RMS < 0.23 seconds), it can be finalized in DRP, without further processing in Jiggle. These usually have SRC set to "hypomag" in the final catalog.
  • If the event is an earthquake, and it has magnitude M > 1.95, or RMS > 0.23 seconds, the analyst should accept the event in DRP, which sends out an alarm message stating that the event was human-reviewed. The event solution still needs to be reviewed, refined, and finalized within Jiggle.
  • Delete event is generally not done in the DRP; it is preferred practice to delete events within Jiggle.
  • More DRP details from SCSN wiki

Which databases? Model...

Waveform screenshot

Earthquake (Regional, Teleseismic)

TODO

Regional earthquakes are outside the SCSN network boundaries. Parkfield, Coalinga, Mammoth, Nevada.

Baja California: north of 31 degrees North latitude, and whose arrivals are not too emergent to pick reliably.

If a large enough event is outside network boundary (for example in Parkfield), the authoritative network solution (for example, NC) will be manually imported through Jiggle.

Teleseismic earthquakes are large (at least M > 5) earthquakes located over 1000 km away from southern California, often on the other side of the world. They have long-period waveforms that arrive at all stations in the network almost at the same time, and the duration of these waveforms can be several minutes long.

From other networks – import their solution?

Edit, add comment

Set GTYPE in DRP, Jiggle. Only for earthquakes. GTYPE - where is this attribute in database?

Telestifle?

Teleseismic events: (M > 6.5) are added by the "sedas" program, import solutions from NEIC? Keep in catalog Do not finalize teleseismic event solutions, their processing state will be "A" for automatic. Teleseismic events are checked to see if they match those received from the NEIC through PDL. (TODO check for accuracy)

Example of catalog + map

Waveform screenshot

Trigger

TODO:

The automatic catalog from RT AQMS includes events have their origin event type (ETYPE) set to "trigger", and their origin subsource (SRC) set to "RT" followed by a number.

These events have passed through the Earthworm subnet trigger algorithm, consisting of the carlstatrig and carlsubtrig modules, instead of binder. Subnet triggers are used to detect events in sparser areas of the seismic network, where binder did not detect events; in southern California, subnet triggers are used in the eastern, northern, and offshore western parts of the network.

Triggers are just a collection of stations that triggered on a relatively low threshold. Triggers have an associated time, but no location or magnitude. They may or may not be from an earthquake. 5-10% of finalized earthquake events in the final SCSN catalog originate from the subnet triggers, and they are usually very small or emergent events.

At the SCSN, "trigger" events that passed through the Earthworm subnet trigger end up in the TRP, where the analyst takes a first pass at post-processing by visually inspecting the waveforms:

  • If the event is not an earthquake (for example, if the waveforms look like noise), the analyst should delete the event in TRP, which deletes the trigger from the database forever. Triggers deleted in TRP never appear in Jiggle, so it is good practice to only delete triggers where the analyst is confident that it is not an earthquake.
  • If the event waveforms look like an earthquake, the analyst should accept the event in TRP, and has the option to set the origin event type ETYPE within TRP to "earthquake" by clicking on the "Set Etype" button. The event solution still needs to be calculated and finalized within Jiggle.

For the remaining accepted triggers, the analyst can load the trigger event into Jiggle and view its waveforms.

Which databases? Model...

Trigger – many values not in the table

Waveform screenshot

Quarry Blast

Quarry blasts from mining operations within the SCSN boundaries are often detected by the automatic RT AQMS software. Quarry blasts originate from an outward explosion on the earth's surface, in contrast to earthquakes that originate from shear slip on a fault at some depth underground.

Figure

The screenshot above shows an example of waveforms from a quarry blast, which have a "ringy" long-duration and low-frequency S-wave. The screenshot below shows a map with the quarry blast location (blue dot with pink arrow pointing to it), which is located near the "CUSHENBURY" quarry (purple X's indicate known quarry locations in southern California).

Figure

TODO

Right click popup menu, Select all -> Quarry Check?

Message View

*  70284855 CI 2019-06-14 22:01:31.42   33.8720 -117.4987   1.65  1.34 Ml  eq  L ---      CI 02  H   2  -  H 03E   1.13  0.52    2.4 mi N   (   6. azimuth) from CORONA QRY
*  70284927 CI 2019-06-14 22:47:10.95   33.8353 -117.5162   2.47  1.35 Ml  eq  L ---      CI 02  H   2  -  H 03E   2.00  0.47    0.8 mi WSW ( 256. azimuth) from CORONA QRY
*  70288207 CI 2019-06-16 23:22:46.02   35.0513 -117.6587   0.56  1.31 Ml  eq  L ---      CI 02  H   2  -  H 03E  -0.27  0.83    1.4 mi ENE (  57. azimuth) from BORON QRY

Gazetteer

During daytime, located near known quarry? Single event - box pops up saying it is a potential quarry blast

Edit, add comment

Set ETYPE in DRP, TRP, Jiggle

Once you declare event as a quarry blast, you get a lot of ‘stale’ messages. Depth is set to be at the surface, so this requires re-locating and re-computing magnitude.

Inventory of all possible quarries? from SCSN Wiki

Waveform screenshot

Other Exotic Events

TODO: different event types (more exotic types)

Edit, add comment

Set ETYPE in DRP, TRP, Jiggle ETYPE - where is this attribute in database?

Sonic booms are sometimes detected by the SCSN. They may originate from test flights or training runs at military bases in southern California. Sonic booms usually occur from aircraft, but sometimes are the result of meteors. Sonic booms travel at the speed of sound, which is much slower than the speed of seismic waves, so the waveforms are spread farther apart in time at the different stations.

Sonic booms are saved if they show strongly on “a significant number” of stations, if they generate any public inquiries, or if they are requested specifically by a researcher. Space shuttle re-entries are routinely saved. (TODO link to SCSN wiki page)

Artillery fire from military training at Marine Corps Base Camp Pendleton, located within the SCSN boundaries, is often detected by the SCSN. There are usually several impulsive signals, occurring very close together in time, and they travel at the slower speed of sound.

Figure

The screenshot above shows an example of waveforms from artillery fire located at Camp Pendleton. The screenshot below shows how the artillery fire is recorded in the final catalog within Jiggle. The ETYPE is set to "chemical blast", the location and magnitude parameters are all set to 0, the magnitude type MTYP is "Mun", and the COMMENT field has a note stating "Camp Pendleton Mortar/Artillery Fire".

Figure

TODO

Examples of exotic event waveforms from PNSN: https://pnsn.org/earthquakes/exotic-events

There are 29 possible event types for the database, and each event type is identified by a 2-character code in the "eventtype" table within the CISN schema. The SCSN wiki contains an inventory of all possible event types.

TODO drop-down menu, and set common event types within Properties TODO up-to-date event types?

Waveform screenshot