• Antelope Release 5.5 Linux 2.6.32-220.el6.x86_64 2015-04-21

 

NAME

mwap - multiwavelet array processor for three-component seismic arrays

SYNOPSIS

mwap db [-phase phase -sift expression -pf pfname]

SUPPORT


Contributed code: NO BRTT support.
THIS PIECE OF SOFTWARE WAS CONTRIBUTED BY THE ANTELOPE USER COMMUNITY. BRTT DISCLAIMS ALL OWNERSHIP, LIABILITY, AND SUPPORT FOR THIS PIECE OF SOFTWARE.

FOR HELP WITH THIS PIECE OF SOFTWARE, PLEASE CONTACT THE CONTRIBUTING AUTHOR.

DESCRIPTION

The mwap program is a software tool that performs a novel form of coherent waveform processing. The current version is exclusively designed for application to three-component seismic arrays. It does plane wave processing so it is NOT applicable to data from events inside an array. It is designed for large aperture broadband array recordings of teleseisms but will work equally well on three-component small aperture, high frequency arrays. The program simultaneously estimates five sets of observables: (1) the slowness (phase velocity) vector of a best fit plane wave, (2) static time shifts relative to this best fit plane wave, (3) amplitude statics of amplitudes relative to the array stack at each station, (4) particle motion ellipse estimates for every station in the array, and (5) an array average particle motion estimate.

The mwap builds on a unique concept of multiwavelets that are closely akin to multitaper spectral estimates. The essence of their use is that multiwavelets should be thought of as a set of narrowband filters with optimal resolution in the time and frequency domains. That is, they have the narrowest possible bandwidth for a specified time duration or vice versa. The major use of these special functions in this program is to measure phase. Most of the manipulations in the program, however, involve phase measurements made on transient signals by using complex pairs of wavelets that are similar in form to windowed sine and cosine functions. The "multi" modifier comes from the fact that multiple, orthogonal functions are used to produce independent estimates in the same band. This permits robust averaging in an attempt to make estimates more stable and simultaneously provide objective error estimates of the resulting parameters.

Seismic data are read from an input css3.0 database. The program looks at the event, origin, assoc, arrival, wfdisc, site, and sitechan tables and the integrity of the database is assumed. The actual reads use the current Antelope trace library so whatever datatypes the trace library supports can be read by this program. The program will attempt to process the entire database using evid-based grouping. Use a sift parameter if subsets of the data are desired.

It is important to recognize that this program is not intended as a raw processing module. It expects to be handed a set of associated arrival picks are that are within a half-cycle of being correct at the lowest frequency present in the data. It will almost certainly yield total garbage if the picks are not reasonable. Extensive use of robust estimators help some in stability, but the number of free parameters seem to render the results somewhat unpredictable in the presence of strong outliers.

The major input parameters to this program are through a parameter file that defaults to mwap.pf. The list of parameters is long and described in detail in a related html document (see below). The major output of the program is a series of extension tables to css3.0 called: mwslow (slowness vector estimates), mwtstatics (time statics table), mwastatics (amplitude statics table), mwpm (particle motion estimate table), mwsnr (holds signal to noise ratio estimates for different analysis bands), and mwavgamp (array average amplitude estimates in each band).

COMMAND LINE ARGUMENTS

  • db
    Datascope database name to process.
  • -phase
    This parameter allows specification of an alternative phase to the default P. The trailing character is a phase name is use to distinguish P and S phases. e.g. S is assumed to be an S wavefield at the array. The distinction is important because S phases are rotated differently and S velocities are used to compute elevation statics instead of P velocities.
  • -sift
    The given expression is applied to a basic arrival time view (event, origin, assoc, arrival) to reduce the data to be processed. For example, to process only evid 245, use -sift "evid==245".
  • -pf
    Use pfname as the parameter file instead of the default mwap.pf

FILES

Requires schema extension MWavelet1.3 to be stored in an accessible place and be defined in the database descriptor.

PARAMETER FILE

Look for current html documentation at http://aesn.geology.indiana.edu/aug/aug.html. The detailed desription of parameters for mwap is under construction.

SEE ALSO

mwapbavg(1), mwtransform(3), mwstatistics(3) and html documentation
which is much more complete.

BUGS AND CAVEATS

The fundamental tradeoff between the estimated slowness vector and a best fit plane through a surface of residuals makes the convergence of this algorithm less stable than one might wish. If problems are found in a given event, try checking the picks and reprocessing that event.

AUTHOR

Gary L. Pavlis, Indiana University
Antelope User Group Contributed Software
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