Seismological Processing JMTS

Availability of Jmts 2009.08 (updated 17 August 2009)

The next release of the new Jmts, containing a multitude of new features, is now available for use by our customers. Please read the release notes carefully before installation and use.

• Release Notes (zip)
• Comparison of Source Parameters
• Jmts 2009.08 Linux (32-bit)
• Jmts 2009.08 Windows (32-bit)

Overview

The seismological software package provides routine and advanced analysis of seismic events, in a Microsoft Windows or Linux environment.

• 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.
• Jmts 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.
• Jmts processes three or one -component waveforms recorded either by geophones or accelerometers.
• Source parameters produced automatically by the Run Time System, may be modified after interactive reprocessing.

Preprocessing of the waveform

Waveforms click to view enlargement

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.

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

Event Location click to view enlargement

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.

Source Parameters

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

The 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.

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.

This page last updated: January 2007