Eqassemble Overview

Eqassemble is the first process in the earthquake-processing mega-module (sometimes referred to as "the sausage") that produces earthquake locations for the Earthworm system. Only eqassemble, the first link in the mega-module, is listed in startstop's configuration file to be started by startstop. Eqassemble 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 (eqassemble) 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.

Eqassemble is the result of merging three other Earthworm programs: eqprelim, eqrapid (used only at Caltech), and eqproc. This merger was needed for the CISN project. It results in a single module that can release event messages meeting any of three different rule sets that are derived from the original programs' rules. By merging the three programs into one, we also gain by having to run only a single sausage instead of three.

After starting up the next link in "the sausage," eqassemble's main job is to gather information from picker(s) and binder, to decide when en event is ready for release, to assemble all the information related to that event, and to pass it on to the next event-processing sub-module.

Eqassemble collects messages from the picker(s) (TYPE_PICK_SCNL and TYPE_CODA_SCNL) and from binder (TYPE_QUAKE2K and TYPE_LINK). A TYPE_PICK_SCNL message contains an observed P-wave (or S-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_CODA_SCNL 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.

Eqassemble maintains two circular buffers:

1. Pick list

Contains the most recent MAXPCK (=1000) picks and their coda and link information (related by installation id, module id and pick sequence number) and the system-time that the pick was entered.

2. Quake list

Contains the most recent location and status of the last MAXHYP (=100) event ids and the system-time that the location was entered.

Eqassemble applies up to three configurable rule sets to decide when to release event messages. These rule sets are:

preliminary rule:

N (=25) P phases associated with the event. At Menlo Park, this is used to publish a preliminary location (with no magnitude) for an event of potential interest to the public. This event message is assigned version 0.

rapid rule:

release the event message N (=90) seconds after either origin time or detection time, provided there are at least M (=5) P phases associated with the event. This message is used in CISN to initiate Ml calculations. The waiting time is to allow sufficient waveforms to be available to compute local magnitude as rapidly as feasible. This event message is assigned version 1.

final rule:

release the event message N (=60) seconds after binder has stopped updating the solution, provided there are M (=4) associated P phases. In addition, eqassemble can optionally wait for the TYPE_CODA_SCNL messages for this event. If eqassemble is configured to wait for codas, it will wait until coda messages are received for all associated picks; but not more that 150 seconds. The 150 second wait duration is not configurable, since it is based on the 144 second coda time of pick_ew. This event message is assigned version 2.

If eqassemble is configured not to wait for codas, then the event message produced by eqassemble will contain no coda durations. This option is intended for networks which do not want to produce duration magnitudes with the Earthworm sausage.

Occasionally, binder will decide to cancel event on which it has been working, It indicates this by reducing the number of associated picks to zero. If eqassemble sees this happen after it has released any version of the event message, it will issue a TYPE_CANCELEVENT message.

Occasionally, eqassemble will receive more TYPE_QUAKE2K and TYPE_LINK message for a given event id after it has finalized that event. Eqassemble will note these messages in its log file, but it will never send another TYPE_EVENT2K message thru the mega-module for that event id.