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wiki:evansassoc
Last modified 18 months ago Last modified on 03/25/12 13:33:42

# Earthworm Module: evansassoc

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## Function

evanstrig monitors waveforms for long-period signals; evansassoc associates LP triggers into events.

## Details

The evanstrig program is an adaptation of lptrig. Evanstrig runs John Evans' long-period trigger algorithm on single-channel TYPE_TRACEBUF messages and produces single-channel triggers. These triggers can then be associated into "events" by the moduleevansassoc.

The evansassoc program associates long-period triggers from several scn's. The association rule is that triggers from a certain number of scn's must be received within a specified time interval. The association parameters are specified in evansassoc 's parameter file .

NOTE: evanstrig will only work on 100 hz data!

The details of John Evans' long period trigger algorithm are discussed in the following two papers:

A Teleseism-Specific Detection Algorithm for Single Short-Period Traces, Bull. Seism. Soc. Am. 73, 1173-1186, Evans and S.S. Allen, 1983.

Reliable Automatic Detection of Long-Period Volcanic Earthquakes at Long Valley Caldera, California, Bull. Seism. Soc. Am. 85, 1518-1522, Evans and Pitt, 1995.

### Example Configuration File

    #
    #           evansassoc's Configuration File
    #
    MyModuleId       MOD_EVANSASSOC    # Module id for this program,
    InRing           PICK_RING         # Transport ring to find triggers on
    OutRing          HYPO_RING         # Transport ring to write output to
    HeartbeatInt     30                # Heartbeat interval (s); 0=no heartbeat
    LogFile          1                 # 1=write log file on disk; 0=don't

    # List the message logos to grab from transport ring
    #                Installation       Module       Message Type
    GetTriggersFrom  INST_WILDCARD   MOD_WILDCARD      # trigger

    # LP-trigger association parameters:
    TriggerTimeLimit  17    # seconds; Set to (array aperture)/(8 or 10 km/s).
    CriticalMu        10    # number of triggers within TriggerTimeLimit.
    CriticalNu        10    # ..."... Set equal to CriticalMu.

    # Parameters for saving seismograms:
    MinEventTime     90     # total record length (s) of "normal" event
    MaxEventTime    105     # total record length (s) of "big" event
    PreEventTime     15     # pre-event portion (s) of event record

    EventIDfile  nextlp.id  # name of file containing next valid eventid
                            # this file should live in EW_PARAMS directory

    # List any other channels (time code, non-seismic, etc) that should be
    # included in every event message. Wildcards (*) may be used in any field.
    # List one SCN per line, as many as you need:
    #           sta chan network
    AddChannel  MSL  VHZ  NC
    AddChannel  MDR   *   NC

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