Eqprelim is a first process in the earthquake-processing mega-module (sometimes referred to as "the sausage") that produces preliminary earthquake locations for the Earthworm system. Eqprelim is very similar to eqroc, which produces Earthworm's final event locations. Only eqprelim, the first link in the mega-module, is listed in startstop's configuration file to be started by startstop. Eqprelim then starts the next process, specified in its "PipeTo" command, and communicates with it via a one-directional pipe. Each newly created sub-module starts the next link in the same way. From startstop's point of view, the whole mega-module inherits the name of the first link (eqprelim) and that's the only name it displays. From statmgr's point of view, all processes within the mega-module share one module id, one heartbeat, and one descriptor file. However, each sub-module has its own configuration file and its own log file.
After starting up the next link in "the sausage," eqprelim's main job is to gather information from picker(s) and binder, to decide when it's time to report a preliminary hypocenter for a given event, to assemble all the information related to that event, and to pass it on to the next event-processing sub-module.
Eqprelim collects messages from the picker(s) (TYPE_PICK2K and TYPE_CODA2K) and from binder (TYPE_QUAKE2K and TYPE_LINK). A TYPE_PICK2K message contains an observed P-wave arrival-time and amplitude for a given seismic channel along with the installation id, module id, and pick sequence number; the picker releases the pick message within ~3 seconds of a P-wave detection. A TYPE_CODA2K message contains coda duration and amplitude information along with the installation id, module id, and sequence number of the pick it relates to; the picker releases the coda message up to 144 seconds after its corresponding pick message. A TYPE_QUAKE2K message contains an event id number, origin time and hypocenter; binder issues a new quake message each time it associates a new pick with [or deletes pick(s) from] a given event id. A TYPE_LINK message contains an event id, an installation id, a picker module id, a pick sequence number and a phase identifier; binder issues a new link message for every pick it associates with (or deletes from) an active event.
Eqprelim maintains two circular buffers:
Each time eqprelim receives a TYPE_QUAKE2K message, it checks to see how many phases are associated with that event id. If the number of P-arrivals associated the event is greater than or equal to "NumPickNotify" (set in the configuration file), eqprelim initiates preliminary earthquake processing.
Eqprelim will initiate only one preliminary location per binder event id, so NumPickNotify should be set at the number of phases where most event locations become stable. Often, no coda information or only poor coda information is available at the time eqprelim initiates the preliminary location. Thus most preliminary locations will have poor or absent duration magnitudes.
Note: It is possible that binder may kill an event (decide it was not real) after eqprelim has initiated the preliminary location. Eqprelim does not send out any kind of "event killed" messages. One must assume that if a final location (via eqproc) does not arrive within a given time interval (say 5-10 minutes), then the preliminary location was for a busted event.