Earthworm Module: evansassoc
Contributed by:
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
