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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: The EEV program is the interactive program for working with single events in the database. The program is 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).

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, rotate seismograms, display theoretical arrival times for IASP91 phases to help identifying global phases and do spectral analysis. MULPLT can be used from EEV 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. 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.

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:

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.
Interactive phase picking, earthquake location, magnitude etc done with EEV. Automatic phase picking is also possible at this stage.
Database is updated (UPDATE) once a suitable interval has been processed interactively, usually a month. Updating means permanently storing the hypocenters etc in the database.
Make hypocenter maps with EPIMAP.
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.

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. 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/MULPLT as above and possibly extract additional data out of the continuous data base and put it into the event data base.

It should be noted that data collection and step 1 to 3 is fully automated using SEISNET [Ottemöller and Havskov, 1999].

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.

next up previous contents index
Next: 5.1.2 Source parameters Up: 5.1 Short user guide Previous: 5.1 Short user guide   Contents   Index
Peter Voss : Tue Jul 2 07:59:27 UTC 2019