5.1.1 Routine processing

The main work of a seismic observatory is to quickly process and organize incoming data from different sources. SEISAN has a simple time ordered database (see later section) and a set of programs for these tasks. The most important programs are:

EEV and SE: The EEV and SE programs are the interactive programs for working with single events in the database. The programs are used to navigate in the database to find a given event as well as for housekeeping (splitting, merging and deleting events). Once an event has been selected, a large number of options are available like phase picking, earthquake location, fault plane solution, macroseismic information etc. All results of the interactive processing are stored in the database (S-files). EEV and SE have similar optionss and it is possible to use EEV options from SE. EEV is working from the prompt line while SE is using a graphical interface.

MULPLT: This is the general plotting and signal analysis program and can be used to pick phases and amplitudes, correct for instrument response, produce Wood-Anderson seismograms for determining Ml, simulate WWSSN SP and LP records, determine azimuth of arrival for 3 component stations, make spectrograms, rotate seismograms, display theoretical arrival times for IASP91 phases to help identifying global phases and do spectral analysis. And more. MULPLT can be used from EEV and SE or as a stand-alone program.

FK and PFIT Determining apparent velocity and back azimuth using an array of a local /regional network.

HYP: This is the general program for hypocenter location and is based on HYPOCENTER [Lienert et al., 1986; Lienert and Havskov, 1995]. The program can use nearly all common crustal and global phases (8 character ISC codes), locate teleseismic events using the IASP91 model and use observed azimuth and apparent velocity. The program can therefore be used with all types of input data whether from single stations or arrays. HYP can be used from EEV or as a stand-alone program. HYP is integrated into SE proving a superior interface giving more feedback and options to the user, than the prompt operation. Apparent velocity is currently only used for starting location.

EPIMAP: This is the general hypocenter plotting program for making epicenter maps and hypocenter profiles. The hypocenters can be plotted with elliptical error ellipses and EPIMAP can also be used for interactive selection of events in polygon areas. For plotting hypocenters, there is also an interface to GMT. MAP is a simple version of EPIMAP requiring no input of parameters, just the Nordic file with the hypocenters. A simlar program using GMT is MAPG. Fault plane solution can also be plotted.

BUL: The function of this program is to produce a bulletin. The user can tailor the appearance to local needs and the program can produce bulletins of hypocenters only or both hypocenters and phase readings.

In addition to the above programs, several programs are available for database creation, input and output of large data sets and conversion and manipulation of waveform data.

In order to get an idea of how routine processing works, some examples of routine processing will be given below.

Case A: Telemetry network with 32 channel central recording

The network generates waveform event files, which are transferred to SEISAN. The tasks are:

1:
Convert waveform files to SEISAN format or any of the other formats used by SEISAN. It is likely that the format is MiniSEED in which case no conversion is needed. (many events can be converted in one operation). Inspect events with MULPLT. From MULPLT, false triggers are deleted and real events are put into the database. Events are at this stage identified as local, regional or distant. Phase picks can be done at this stage, but is usually done later.
2:
Interactive phase picking, earthquake location, magnitude etc done with EEV oe SE. Automatic phase picking is also possible at this stage.
3:
Database is updated (UPDATE for many events, outside EEV or SE or oen by one in EEV or SE) once a suitable interval has been processed interactively, usually a month. Updating means permanently storing the updated or newly calcualted hypocenters etc in the database.
4:
Make hypocenter maps with EPIMAP, MAP or MAPG.
5:
Produce a bulletin with BUL.

Case B: 3 telemetry networks and one broad band station

The routine is the same as above except for one additional step between 1 and 2. Since several data sets are available, some of the detections from different networks or the broad band station might correspond to the same event. There are now two options. The first is to merge the waveform files for corresponding events and then put the events into the database. The second option is to put all real events into the database and then do the merging from EEV or SE.

Case C: A mix of stations and networks and additional phase readings

The steps are as in case B except that before step 2, the additional phase data is put into the database. In this case the merging of events must be done with EEV

Case D: A network recording all data in continuous mode into a SEISAN continuous data base or now more likely a SeisComP continuous data base.. In addition, there is likely to be network wide triggering put into SEISAN. In this case it is a question of inspecting the triggers with EEV or SE/MULPLT as above and possibly extract additional data out of the continuous data base and put it into the event data base. another option, which now is becomming more common is to put a reference into the S-file where to find the data in the continuous data SeisComP database so it is possible to plot the corresponding waveform data without having any event waveform files.

Example of using EEV for interactive processing:

Find event in default database nearest the given date and time: EEV 1999020303
Once EEV is started, an EEV prompt is given and different EEV options are available. Examples are: E: Edit event, P: Plot event, L: Locate event, F: Make fault plane solution, d2201: Find event nearest day 22 at 01 hour, MAP: Start EPIMAP to show earthquake location and SAC: Start SAC processing of event using all parameter and waveform data from SEISAN database.

The above examples have mostly described the interactive processing of single events. However, once the data is in the database, operations can be done on the whole database, for any time interval or for events fulfilling certain criteria (like magnitude, area etc). Examples are relocating events, extracting data and determining coda Q.

Peter Voss : Fri Nov 12 10:33:10 UTC 2021