REF TEK Interactive Seismic Analysis Program - COMPASS
COMPASS is very powerful and user-friendly interactive software providing to the end-user both weak and strong motion comprehensive data processing tools. COMPASS has seven drop down menus. Four of the menus (File, View, Time Domain, and Measurement) are for data utilities and previewing and pre calculation data filtering and measuring. The other three menus (Frequency Domain, 3-d component, and Location) are for calculation of earthquake physical characteristics.
View Menu Commands Overview
This menu provides for manipulation of seismogram preview settings for the user. The menu commands of the View menu manipulate the display of the data to optimize visual analysis to determine the data’s importance to the user. The display data can be changed with the following menu items:
Time Domain Menu Command Overview
The Time Domain file covers the following broad operational topics which include data filtering, and pre-calculation parameters for use to determine earthquake physical characteristics:
Frequency- Domain Menu Command Overview
The Frequency-Domain menu of the COMPASS software covers the following broad operational topics, some which are used to quantitatively characterize the earthquake:
3-d Component Menu Command Overview
The 3D-Component menu of the COMPASS software covers the following broad earthquake characteristics:
Measurement Menu Command Overview
The Measurement menu of the COMPASS software covers the following selections of measurement functions used in the calculation of the earthquake characteristics. The Pick Time and list are used to calculate the earthquakes location.
- Pick Time— The pick phase arrivals on the current seismogram are determined by the location of the cursor:
- Pick A/T— Magnitude estimates require the user to supply an amplitude and period estimate for the desired phase.
- Pick Polarization— This menu is ONLY applicable during the 3-d component polarization study.
- Auto Time— This command uses an STA/LTA Auto detector used to automatically detect ‘P’ wave arrivals.
- Auto A/T— Use the Auto A/T command to automatically pick waves with maximum amplitude of the signal inside the preview interval.
- List— To manipulate marked arrivals, amplitudes and polarizations use the List command.
Location Menu Command Overview
The Location menu of the COMPASS software covers the following broad operational topics. An Operator report can also be generated from the Location Command menu:
- Hypo Location— After all necessary arrivals and amplitude measurements are done, use the Hypo Location menu to determine the Earthquake hypocenter and energy parameters.
- Predicted Travel Times— To check how the theoretical travel times table fit the located earthquake use the Predicted Travel Times command.
- Waditi Test Plot— To check the quality of “P” and “S” wave arrivals by linear fit to Vp/Vs ratio (for regional events it is close to 1.73):
- Operator Report — Use the Operator Report command from the location menu to save all measured and computed information about the picks and earthquake location to an ASCII file
After all necessary arrivals and amplitude measurements are done use the Hypo Location menu to determine the Earthquake hypocenter and energy parameters.
Strong Motion Processing
Process records obtained on REF TEK Accelerometers
COMPASS processes simultaneously the following Strong Motion parameters:
- Maximum Acceleration – Peak ground Acceleration.
- Spectrum Intensity – for 5% damping. It is defined as the integral of the pseudo-Spectral velocity curve within 0.1-2.5 seconds.
- Predominant period – period corresponding to the peak value of FFT acceleration spectrum.
- Mean period – period corresponding to the average of the weighted values of acceleration spectrum.
- 2PI*Vmax/Amax – period calculated from the (Peak Ground velocity to Peak Ground Acceleration ratio).
- Maximum Velocity – peak ground velocity
- Maximum Displacement – peak ground displacement
- Cumulative Absolute Velocity
- Arias Intensity
- Arias Duration of strong motion within (5-75%) of Arias charging curve.
- Arias Duration of strong motion within (5-95%) of Arias charging curve.
- JMA Intensity – as Instantaneous Instrumental Seismic Intensity = log (A*V) +0.94.
- MMI Intensity – as = JMA*11/7+0.5.