|
NMT Community Archive >
Earth and Environmental Science >
Independent Studies >
Please use this identifier to cite or link to this item:
http://hdl.handle.net/10136/262
|
| Title: | An adaptive, automatic phase-picking and epicenter locating program based on waveform cross-correlation and its application for processing seismic data in New Mexico |
| Authors: | Yang, Wenzheng |
| Issue Date: | 21-Jan-2009 |
| Abstract: | It is widely observed that seismic sources occurring very close to each other can share
very similar waveforms. Using this property, an adaptive, automatic phase-picking and
epicenter-locating program based on waveform cross-correlation has been developed and
applied to process daily seismic data of New Mexico. The core of this program is a reference
seismic event database, from which the phase and location information of a new event can
be inferred. With a sufficiently complete reference seismic dataset, this program should
produce robust initial seismic phase estimates while greatly improving the handling of false
triggers due to telemetry or other transient noise. These automatic results are designed to be
as precise as the manually processed results.
160 well-picked earthquakes and mining explosions in New Mexico during 1997-2003
were collected as an initial reference event set covering most of the historically active source
regions in the state. Each waveform in the reference event set has a high signal-to-noise ratio
and accurately-picked P and S phases. Two methods were developed to automatically
calculate waveform cross-correlation phase-picking and the location of epicenter.
The first, waveform-pair cross-correlation matching method correlates the most similar
waveform from the reference dataset to each waveform of a new event station by station and
assigns the corresponding seismic phases to the new waveform according to crosscorrelation
lag. Note that a new event may be correlated with different reference events at
different stations.
The second, event-pair cross-correlation matching method correlates the most similar event
from the reference dataset to the new event by stacking the cross-correlation curves of all
common station-waveform-pairs. The second method provides more robust results than the
first method.
Due to the concentration of seismic stations in the Socorro area, an “attracting” problem
developed when the event-pair cross-correlation matching method was applied to process seismic
data of New Mexico. This problem happened when the above method construed distant
events to be local ones, because seismic events occurring more than 200 km from Socorro
usually have weak S-phases and are therefore identified as seismic events from the Socorro
area by the event-pair cross-correlation matching method. To nullify this problem, the spectrogram
event-pair cross-correlation matching method was developed. This method matches event-pair in
the frequency domain, decreasing the effect of “attracting” phenomenon. This works
because within the frequency band of 6-10Hz, the energy of S-phase for local events is
prominent and the background noise energy is very small.
The computer program (PLRR) incorporating these methods has been developed under
Matseis/Matlab (developed at the Sandia National Laboratories) in the UNIX
environment. It is used to detect initial seismic phases and identify locations of local seismic
events in New Mexico from 2000 to 2004. Manual phase repicking and epicenter relocating
are applied to the results given by this program to produce a final, reviewed catalogue. If
there is a new, high signal-to-noise event that is incorrectly located by PLRR (as determined
by the review process), it will be added into the reference dataset. The accuracy of phasepicking
and epicenter-locating thus improves as more data are processed. |
| URI: | http://hdl.handle.net/10136/262 |
| Appears in Collections: | Independent Studies
|
Files in This Item:
| File |
Description |
Size | Format |
|---|
| Yang, Wenzheng.pdf | | 4390Kb | Adobe PDF | View/Open |
|
Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.
|
