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The
seismological software package provides routine and advanced analysis of seismic
events.
- Most of
the development has been focused on implementing a fully automated procedure
for high quality event detection, source location and estimation of the
spectral parameters of local earthquakes.
- The
package has several dedicated interactive functions for phase picking,
location of local earthquakes, magnitude calculation, spectral parameter
estimation as well as moment tensor-, focal mechanism-, and source time
function calculation.
- Xmts
has several visualization routines which display waveforms, rotated components,
polar diagrams, signal energy, P- and S-wave spectra and the displacement
stacked spectrum which is corrected for attenuation. The user has the option
to filter waveforms according to the upper and lower cutoff frequencies.
Several ground motion parameters are displayed as well.
- Xmts
processes three or one -component waveforms recorded either by geophones or
accelerometers.
- Source
parameters produced by the Run Time System (amts), may be modified after
interactive reprocessing.
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Preprocessing of the waveform
The raw waveforms have
to be preprocessed by applying baseline corrections. Instrument correction
for geophones and accelerometers has to be applied to remove the effects of
frequency dependent instrument response to a waveform. A mining environment
may produce a ground loop which could inject a 50/60Hz hum into the signal
which is significantly reduced if not eliminated by the software. Precursory
artifacts generated by anti-alias filters are suppressed by applying several
low pass filters. |
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Determination of P-and S
wave arrivals
The P and S Pick functions
allow the user to manually pick the P and S wave arrival position on a selected
seismogram. The auto picking function will automatically pick the arrival time.
The automatic determination of P-wave arrival is based on multi component
autoregressive techniques (Wiener filter), which is supplemented by detection
algorithms. The S-wave arrival is estimated using a polarization filter and
characteristic function. The implemented procedures for phase detection utilize
travel time information.
Location
| The event
location calculation is performed automatically when the event is accepted.
Numerous reliable methods have been developed to automatically estimate the
source location using P and S wave arrivals and/or S-P differences that are
supplemented by directions towards source and azimuth. Single station
location is provided for three component data. The required accuracy for
location is approximately 3% of the average hypocenter distance from the
source to the stations used in the location procedure for a reasonable
configuration of stations in relation to an event. A higher precision
location is usually achieved with relative location procedures. To use it
several well located seismic events or blasts have to be selected as master
events. |
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Source Parameters
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Spectral
analysis is a standard technique used in studies of local earthquakes. Most
seismic theories predict that the far field displacement spectrum remains
constant at low frequencies and decays at higher frequencies. Source
parameters are calculated from P-and S-wave spectra. Multitaper spectral
estimation techniques are used to minimize the effect of data windowing.
Noise and site effect caused by local geology are reduced by stacking
individual spectra. The spectra of individual seismograms and the stacked
spectrum are corrected for the attenuation effect. The attenuation
parameters are calculated for each event independently; however it is
recommended the option of estimating attenuation using a group of events be
chosen. The following parameters are calculated: scalar seismic moment,
local magnitude, radiated energy of P and S, corner frequencies, source
radius, static stress drop, apparent stress drop and apparent volume. |
Moment Tensor
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moment tensor solution for a seismic event can be obtained automatically.
The reliability of the solutions is quantified by quality indices for the
configuration of the recording stations and quality indices for the
inversion. The inversion is performed in the frequency and/or time domains.
Full moment tensor, after diagonalisation, is decomposed into isotopic and
deviatoric components. For the best double-couple solutions, parameters of
nodal planes are calculated. The user can modify the location of the seismic
event. Time domain inversion additionally provides the temporary evolution
of the source which is a reflection of the source complexity. |
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Data base Filter (Selection
Criteria)
The data can be filtered
according to various event parameters (e.g. magnitude, min. number of stations,
event state, etc.).
User Interface (Separately
Licenced)
This function allows the
user to call a user-defined function. The user must write and compile a
compatible function to execute from this option.
Edit Trigger
This function allows the
user to display and edit the trigger parameters for each trigger associated with
an event (e.g. Quality Factor, P and S Velocity, Lower and Upper Cutoff, etc.).
Print
This function allows the
user to print short and full reports concerning the selected event. The user
also has the option to print the seismograms and/or moment tensor as displayed
on the screen.
RMTS
RMTS is the routine version of XMTS. It has specifications similar to those of
XMTS, but does not have the advanced seismological procedures for calculating
moment tensors, source time functions, orientation of fault planes, site spectra
and polar diagrams.
COPYRIGHT
2002 © ISS INTERNATIONAL LIMITED
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