| The study of observation with various measuring methods on underground water levelmeans supervising its dynamic state, and researching the process of its physicalproperty transformation. The physical or chemical property of the underground fluidsalways be altered by the violent earthquake. Net of underground water level is aimportant constitution of underground fluids observation network, China EarthquakeAdministration. As projects “Ninth Five-Year plan”,”Tenth Five-Yearplan”,”Eleventh Five-Year Plan” put into effect, the size of underground water levelnetwork has become the largest and broadest in earthquake precursory monitoringnetwork, which playing a role more and more important.Considering the current situation of underground water level observation, it is aurgent problem that developing the regular analysis method and digging moreinformation from water level data. Spectrum analysis method could decomposes acomplicated time series into singular harmonic by Fourier Transform, and receives thefrequency and phase formation of the original signal. By this way, we can explain thesignal quantifiable. Spectrum analysis is widely applied in the seismic science.Especially, it plays a dominant role in the earthquake engineering, geophysicalexploration, and nuclear detection. Spectrum method is also applied in theunderground fluids field, and the application concentrates upon fields extracting cycleterm, the state of water level response to barometric pressure, and tides study.This study adopted spectrum method, with Wenchuan, Yushu, and Lushanearthquakes for example, which were violent earthquakes. The data came from wellsin Gansu, Sichuan, Yunnan, Chongqing and Tibet. Most of these wells are locate innorth-south seismic belt, and adopted digital monitors. We selected10series for eachearthquakes to analysis the differences of the spectrum before and afterwards theearthquake, and tried to explain these differences preliminary. Specifically, theperiodogram method was adopted to analysis the spectrum character.There are six sections in this thesis. The first section begins with introduction of thebackground, draws forth the object and method of the study. The second section states the object of study, that is underground water level dynamic condition, and introducesthe monitor methods, static water level and dynamic water level, which is vitalimportant to the study. The third section recommends the spectrum methodssystematically, and makes a probing analysis of the spectrum by different events.This thesis stresses on the fourth and fifth sections. In the first part of fourth section,the background of study region and series is introduced; the way and step ofcalculation is declared in the second part; the results of the calculate on threeearthquakes is provided in the third part, which followed by brief discussion. Thecontent of the fifth section emphasizes on analyzing the rules systematically in bothobservation method and geology structure. The sixth section is the conclusion andoutlook, which might be significant.We found these new discoveries:1.The study of the spectrum of slide and earthquake supposed that spectrum featureschange depending on different kind of events.2.This study take Wenchuan, Yushu and Lushan earthquakes for example, find thatearthquakes alter the fluctuation cycle of water level, which intensify the the lowfrequencies.3.Dynamic underground water level distributes all periods of fluctuation meaner thanstatic water level, but is more sensitive to earthquakes, especially in low frequencyfluctuations. Moreover, dynamic water level lays emphasis on high frequencyfluctuations. This suggest that dynamic water level observation method perform betterthan static method in reflecting earthquake.4.Wells in different tectonic district have different spectrum pattern, but the samedistrict result in similar pattern. Besides that, the rock of aquifer and depth of wellscould also impact the spectrum features of water level. |
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