Seismic warning system using RF energy monitor

US4628299A · kind A · utility

Assignee

• David Pressman · US

Inventors

• Joseph B. Tate · Sausalito, US
• David E. Brown · Pleasant Valley, US

Key dates

• Filing date: Jan 28, 1985
• Grant date: Dec 9, 1986
• Expiry date: Jan 28, 2005

Classification

• Technology area (CPC G): Physics
• CPC primary: G08B21/10
• WIPO field: Control
• WIPO sector: Instruments

Abstract

The ambient broadband radio frequency field strength from broadcast stations is monitored (FIG. 4) by periodic sampling (50, 52). A warning indication is provided if the field strength drops significantly. Drops in such field strength have been correlated empirically with the occurrence of seismic activity, usually several days later. Thus the indication serves as an early warning of an impending earthquake. In one preferred embodiment, a broadband, horizontal, very long monopole antenna (40) was connected to a rectifying and smoothing circuit (FIG. 3) to provide a dc output proportional to the ambient rf field. This voltage is digitized (50), and using a suitably-programmed computer (52), the digital version of the field strength signal is sampled once per minute (78). A cumulative or running average of the minute samples is calculated (80) and held. Once per hour the latest running average is stored (84) and a standard deviation (SD) of the last 24 hourly stored running averages is calculated (88). If the SD exceeds a predetermined value, 0.3 in one embodiment, an alarm is triggered (92). The use of the SD eliminates the effect of day-to-day changes in the amounts of the variatio…