IRISSeismic: triggerOnset – R documentation

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triggerOnset

Event onset triggering

Description

The triggerOnset method of Trace objects uses the numeric vector returned by the STALTA "first break picking" method and a user selected threshold to determine the arrival time of a seismic event.

Usage

triggerOnset(x, picker, threshold, index)

Arguments

`x`	a `Trace` object
`picker`	results from applying the `STALTA` method to this trace
`threshold`	optional numeric value of the threshold at which triggering should occur
`index`	optional logical to return the index (rather than the time) of event onset (default=`FALSE`)

Details

This method simply identifies the point at which the picker first rises above the threshold.

When no threshold is supplied, an appropriate value is calculated from the picker with:

threshold <- quantile(picker,0.999,na.rm=TRUE).

Value

A single value is returned identifying the onset of the seismic event or NA if none is detected. The returned value wil be a POSIXct time by defult or a numeric index if index=TRUE.

Note

The appropriate value for the threshold will depend upon the exact STA/LTA algorithm used and the noise level in the signal.

Author(s)

Jonathan Callahan jonathan@mazamascience.com

Examples

# Open a connection to IRIS DMC webservices
iris <- new("IrisClient")

starttime <- as.POSIXct("2010-02-27 06:00:00",tz="GMT")
endtime <- as.POSIXct("2010-02-27 09:00:00",tz="GMT")
  
# Get the waveform
st <- getDataselect(iris,"IU","ANMO","00","BHZ",starttime,endtime)
tr <- st@traces[[1]]
picker <- STALTA(tr,3,30)

# Identify the onset of the event
to <- triggerOnset(tr,picker)

plot(tr)
abline(v=to, col='red', lwd=2)

IRISSeismic

Classes and Methods for Seismic Data Analysis

v1.6.2

GPL (>= 2)

Authors

Jonathan Callahan [aut], Rob Casey [aut], Gillian Sharer [aut, cre], Mary Templeton [aut], Chad Trabant [ctb]

Initial release