Degtra A4 is a Windows-based computer system designed to process ground-motion time histories for seismology, engineering seismology and earthquake engineering applications. It has been developed at the Institute of Engineering, UNAM, Mexico, where it has been used as a professional and teaching tool for more than 10 years. Figure 7.22 shows a typical view of Degtra A4.

Degtra A4 accepts input ground-motion recordings written in several formats: simple ASCII or binary files, SEISAN format and the standard format of the Mexican Strong-Motion Database.

The program has a nice and user-friendly interface, in which several time-histories can be manipulated at a time. It includes zoom-in/zoom-out capabilities that can be used if only a portion of a recording is of interest.

There are two types of operations that Degtra A4 can perform using strong-motion recordings: operations involving a single recording and operations involving two recordings.

Among the first group, the main functions are the following:

- Scaling. Multiplies the recording by a constant
- Decimation. Decimates the recording by a user-given factor
- Base-line correction: Includes several methods.
- Differentiation: Numerical differentiation with respect to time.
- Integration: Numerical integration with respect to time.
- Computation of Arias' intensity.
- Filtering: Includes high-pass, low-pass, band-pass and band-stop Butterworth filters, as well as Gaussian and Futterman filters.
- Computation of elastic response spectra. Computes absolute acceleration, relative velocity, relative displacement and pseudo acceleration response spectra.
- Computation of inelastic response spectra. Computes required-strength response spectra for fixed ductility demand of bilinear systems.
- Computation of Fourier spectra. Computes and (optionally) smoothes FFT of a time signal.
- Computation of response (acceleration, velocity, displacement) of elastic and inelastic (bilinear) single-degree-of-freedom oscillators.
- Computation of the S-wave response of a soil column of given properties assuming that the time-history is the incident wave field at the base of the column.

The main operations involving two recordings are:

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- Spectral ratio. Computes the (Fourier) spectral ratio between two recordings.
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- Odogram. Displays an X-Y parametric representation (time is the parameter) of two recordings, typically ground displacements, in order to observe particle trajectories.
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- Addition/Difference. Computes the sum or difference of two recordings. This is useful, for instance, to identify rocking or torsional motions in buildings.
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- Rotation: Rotates two components of the ground motion to arbitrary angles.
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- Cross-correlation: Computes cross-correlation between two signals.
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- Coherence: Computes coherence between two signals.

Degtra A4 includes an on-line help file with details about the meaning of required parameters, techniques used, and use of Degtra A4 itself. It is available in two versions: one for Windows 2000 or lower and another for Windows XP. Installation is made with a typical Windows executable setup file. The distribution is found in directory SUP.

Degtra A4 is currently in Spanish, English version in preparation.

For questions please contact:

**Mario Ordaz**, Institute of Engineering, UNAM

mors@pumas.iingen.unam.mx