Developments in microprocessor technology are having considerable influence on the way engineering seismic data is collected, processed and analysed. Case studies of two seismic instrumentation systems and their applications are described.

A microcomputer enhanced engineering seismograph, Geoseis-Merlin, has been developed as a portable repackaged Apple unit with a 5 inch monitor, internal printer, bubble memory and disk drive to give on-site processing and results. The unit includes a multi-channel, 12 bit analogue to digital converter card with programmable gain amplifiers, and the system is designed to operate in the field as a self-contained, six channel, seismic processing system. Menu-driven software operations include: data capture incorporating a pre-trigger memory facility for blast monitoring, concatenation and editing of files, display of seismic time data, seismic refraction analysis of up to 24 channels, power spectral computation, display of power and attenuation spectra, spectral smoothing, and digital filtering of waveforms. The system can also be used as an interface to existing seismographs or to the radio telemetric seismic monitoring system.

A 24 channel, radio telemetric, seismic monitoring system has been developed, consisting of six portable outstations which can be positioned up to 2 km from a base station located in a Land Rover or site office. Each microcomputer controlled outstation has one air overpressure and three ground vibration channels for recording up to 16 sec of pre-and post-trigger data. Communication between each outstation recorder and base is via a UHF duplex telemetry link which is used to activate and program each outstation, to maintain synchronization and to transfer data from each recorder to the microcomputer controlled base station. Here the captured seismic event can be stored on cassette, displayed on a 5 inch monitor, or transferred to an Apple II microcomputer (Geoseis-Merlin) for processing.

The case studies outline the application of these systems in engineering geology to bedrock depth determination, rock mass characterization, and the monitoring of quarry blasting.

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