Microseismic Observation in the Vicinity of Hakusan Volcano
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Microseism
Microseism
Swell
Seismogram
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The simulation experiment of the vehicle action on pavement was carried on. In the progress of the experiment, HZ-MS48 microseismic monitoring system was used to collect microseismic waves. And these microseismic signals were disposed and analyzed. It introduced the scheme and the process of the data collecting experiment. After that, several types of microseismic waveform were compared and discussed. Also shock waves for transmitting characteristic in pavement base were studied. At the same time, taking a typical microseismic event location as a case, the precision of microseismic event location was confirmed, which put forward a new way for monitoring traffic vehicles.
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Base (topology)
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Microseisms are ground vibrations caused largely by ocean gravity waves. Multiple spatially separate noise sources may be coincidentally active. A method for source separation and individual wavefield retrieval of microseisms using a single pair of seismic stations is introduced, and a method of back azimuth estimation assuming Rayleigh‐wave arrivals of microseisms is described. These methods are combined to separate and locate sources of microseisms in a synthetic model and then applied to field microseismic recordings from Ireland in the Northeast Atlantic. It is shown that source separation is an important step prior to location for both accurate microseism locations and microseisms wavefield studies.
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Rayleigh Wave
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Three series of simultaneous wave and microseism records are examined. They give a clear indication that bands of microseismic waves from different sources can be distinguished by submitting seismograph records to frequency analysis. The agreement between the results of analysis and the theoretical expectation from the prevailing meteorological conditions appears to justify the assumption that microseismic waves of different periods travel independently. Under the simple meteorological conditions that have been studied, each band of microseismic activity can be identified with a band of sea waves of twice its period. The existence of this two to one ratio between the period of waves and microseisms affords some confirmation of the theory that microseisms are produced in a region of interference between similar wave trains travelling in opposite directions either near the coast or in deep water.
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Seismometer
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In general, microseisms are a nuisance.It is n9w quite widely agreed that microseisms are channel waves, similar in nature to the Lg and Rg waves.It is not at all unusual to observe microseisms which have traveled over distances of continental proportions.In order to determine the direction from which the microseisms come and to investigate in more detail the characteristics of microseismic disturbances, we established a tri-partite system on Mount Palomar.The array consisted of three stations, located at the vertices of a triangle, which was about 2,500 feet on a side.Two Benloft strain seismographs and one Bentoff vertical pendulum seismograph were installed in a strain vault at one location.One vertical pendulum seismograph was installed at a second location, and two horizontal and one vertical pendulum seismographs were installed at a third location.Portions of the records which were obtained on two consecutive days are included in Figure 1.The direction of approach can be calculated from the displacement between the peaks on the three verticals.These observations indicated that the waves practically always come from the coast.The direction of approach generally lies between north-northwest and south-southwest.The horizontal pendulum traces in record (a) are parallel.This indicates'that the horizontal motion is in a northeast-southwest direction and vice versa.Everything on record (a) points to a Rayleigh type motion.Shear waves predominate on record (b).The fact that the horizontal pendulums are opposed to each other indicates that the motion is in a northwest-southeast direction.The horizontal component of displacement is, therefore, perpendicular to the direction of propagation.The sum of strain components is practically zero, as it should be for a horizontally polarized shear wave.The vertical pendulums show some stoa1!motions.This is to be expected, since some Rayleigh type motion is always present.Both of these waves are character~ ized by six-second periods, but usually the Rayleigh type motion predominates.Among the many other types of microseisms which are observed are the twosecond microseisms with wavelengths between about one-third and one-half the wavelength of the six-second waves and practically the same velocity.These waves originate near the coast--probably on the continental shelf.it is generally believed that they are generated by turbulent air masses over the continental shelf.The horizontal pendulum and the horizontal strain seismographs show practically only the six-second waves and very little of the shorter waves.We were puzzled by the [act that here we had a wave which traveled with the Rayleigh wave velocity but possessed mainly a vertical component.Fortunately, Dr. Press could give us the probable solution.Drs.
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