Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2000-02-17
2002-03-12
Lee, Benjamin C. (Department: 2736)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S683000, C340S669000, C340S665000, C340S689000, C073S659000, C073S649000, C073S658000
Reexamination Certificate
active
06356204
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to detection of impending earthquakes and more particularly, the invention relates to a detector and method for discriminating between general earth tremors and tremors which are precursors to an earthquake. Further, the invention relates to a relay-type earthquake detector for relaying a warning signal to remotely located sensors.
BACKGROUND OF THE INVENTION
It is well documented that earthquakes have characteristic wave forms and vibration characteristics which are particularly useful for identifying earthquake caliber vibrations from simple random vibrations which are typically encountered in earth formations. Typically, an earthquake tremor results in the propagation of P-(primus) waves, which are propagated as compression and rarefaction and as well involves S-waves (secundus), which waves propagate an orthogonal angle to the direction of the wave. Generally speaking, the P-waves have a natural frequency of approximately 5 Hertz(Hz) while S-waves have a frequency significantly less than the P-waves. The S-waves have a significantly larger amplitude than the P-waves and therefore are the waves that are principally involved in the destruction to structures. P-waves typically travel at a faster rate from an epicenter to a given locale in comparison with S-waves. Thus, detection of P-waves can serve as a warning of the arrival of S-waves at a given location, in particular a location at some remove from the epicenter.
One of the primary difficulties in earthquake detection relates to the time factor involved in detecting tile P-waves. As will be realized, if P-waves can be detected as early as possible, this provides time for evacuation etc., of a building or area in order to avoid potential human injury caused by the arrival of S-waves which, as indicated above, are the chief destructive waves transmitted by geological formations. Early detection of P-waves has conventionally been difficult.
The art has previously proposed various detectors and other arrangements to measure P-waves to portend S-waves. However, in existing arrangements, one of the primary difficulties is providing sensitivity sufficient to detect P-waves at a distance from the epicenter of an earthquake without incurring large costs. A further difficulty has been encountered in that there is often difficulty resolving false alarms from a real earthquake, due to interference in the instrumentation by extraneous vibrations or other frequencies. It is desirable to provide a detector capable of discriminating between P-waves and ordinary, everyday ground and building tremors unrelated to an earthquake. In particular, detectors mounted to a building should be capable of discriminating between the natural vibration frequencies of the building structure, which are a function of the structure, and frequencies indicative of P-waves. The same may be accomplished by means of an information processing unit that stores vibration data and is programmed to discriminate between frequently occurring frequencies and non-regularly occurring frequencies within the range of P-waves.
Typical of the art that has been patented in this field is U.S. Pat. No. 4,689,997, (Windisch). The reference provides a detector which primarily employs a vertical spring barb mounted on a support. A coupler is supported on the other end of the barb and this coupler is connected through a coil spring to a mass positioned in concentricity with the barb and coupler. The spring and mass components are selected to have a natural resonant frequency corresponding to that of an earthquake tremor or other vibration to be detected. A switching circuit is provided to detonate an alarm once the earthquake frequency is detected. Windisch does not provide an integrated circuit mechanism for detection of earth tremors, but rather relies on a mechanical arrangement in the form of a spring and mass system. As is known, such systems are susceptible to temperature fluctuations which can alter the point at which the apparatus can detect the earthquake frequency. Further, the Windisch arrangement does not appear to provide a system which discriminates between simple extraneous vibration and earthquake caliber frequencies.
Caillat et al., in U.S. Pat. No. 5,101,195, provide a discriminating earthquake detector. The arrangement relies on an electromechanical arrangement having a cantilevered device with a predetermined mass on one end. During movement of the beam, an electrical signal is generated which, in turn, is useful for detection of P- and S-waves. Similar to the above-mentioned detectors in the prior art, the arrangement provided in this reference would appear to have limited utility in that there is no provision for a comparison between earthquake caliber waves and those which are simply extraneous, such as would be encountered in traffic vibration, mechanical vibration in a building, aircraft vibration, etc.
U.S. Pat. No. 5,001,466, issued Mar. 19, 1991 to Orlinsky et al., provides an earthquake detector employing an electrically conductive liquid switch means among other variations thereof.
In view of what has been previously proposed in the art, it is clear that there exists a need for a more sophisticated earthquake detector which is discriminatory between extraneous vibration and earthquake level vibration which is not limited in sensitivity.
A further need is for a detector having the ability to communicate both with other like detectors or servers, in order to improve detection capabilities, and remote locations for coordination of earthquake information.
Accuracy of a detector may also be enhanced by having regard to various P-wave characteristics. For example, it has been found that P-waves are indicative of serious earthquakes if they have a duration greater than a certain value. For most locations, this value is approximately 15 milliseconds, although in some locations this is less. Further, it has been found that earthquakes may be predicted with reasonable accuracy if multiple spaced-apart sensors detect P-waves over tile temporal threshold with temporal overlap existing between the detected P-waves.
SUMMARY OF THE INVENTION
One object of the present invention is to provide an improved earthquake detector capable of detecting earth tremors at a selected frequency and verifying whether the same are indicative of an imminent earthquake. A further object is to provide a detector system comprising a central processor in communication with multiple spaced apart sensors to further enhance advance warning of an earthquake.
Another object of the present invention is to provide an improved discriminatory earthquake detector for discrimination against natural structural vibrations.
Another object of the present invention is to provide a method of detecting vibration signals indicative of an earthquake, comprising the steps of:
providing a vibration detecting means for detecting vibration signals in a structure responsive to ground vibration, the detection means comprising an integrated circuit including a potentiometer circuit;
mounting the detecting means to the structure;
determining the natural vibration frequencies of the structure;
intermittently comparing electronically any extraneous vibration signal different from the vibration signal of the structure; and
determining whether the extraneous signal is within a predetermined earthquake signal level indicative of P-waves.
The step of determining whether the signal is indicative of P-waves may include measuring electronically the amplitude and duration of the vibration signals and determining whether these exceed predetermined minimum levels.
A further object of the present invention is to provide a method for detecting an earthquake, comprising the steps of: providing an earthquake detector having a first sensor for sensing a selected frequency indicative of an earthquake and a transducer means for transmitting and receiving information and an alarm;
providing a second sensor independent of the first for at least receiving information from the first
Guindi Sami
Heidt Robert
Sadri Afshin
Hamrick Claude A. S.
Lee Benjamin C.
Oppenheimer Wolff & Donnelly LLP
Tectonics Research Group Inc.
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