Abstract: A novel method for electronically determining the gross characteristics of he top layer of the earth's crust at a given location by using a passive seismic transducer as a sensing device for sensing background seismic noise in conjunction with as assembly of generally conventional miniature low power electronic components arranged in a system containing analog and logic circuits with a read-out meter calibrated to represent the detected background noise as seismic resonant frequency. The electronic determination of the crust character is in lieu of various conventional soil refractometry tests which are lengthy time-consuming procedures. The seismic resonant frequency has been found to be representative of the thickness and of the property or character of the crust at that particular geographical location.

Abstract: A seismic detection system for detecting persons hidden in vehicles inclu a seismic transducer used as a sensing device and electronic processing circuitry for processing the output signals from the seismic transducer. The electronic circuitry detects output signals from the seismic transducer, and, by counting the number of times the signal crosses a preset threshold during a given time window, makes a logic choice between there being personnel or no personnel in the vehicle. If a person or persons are in the vehicle an output is produced and this output is used to actuate audio and/or visual indicators thereby indicating that a person or persons are in the vehicle.