
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.
triggerOnset(x, picker, threshold, index)
a Trace
object
results from applying the STALTA
method to this trace
optional numeric value of the threshold at which triggering should occur
optional logical to return the index (rather than the time) of event onset (default=FALSE
)
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
.
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)
.
# NOT RUN {
# 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)
# }
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