Research On Comprehensive Application Of Hotan Seismic Array Data, Xinjiang

Xinjiang Hotan small aperture digital seismic array (Hereinafter is called HotanSeismic Array) has been constructed in August,2007, and work normally fromJanuary,2008. This seismic array has accumulated continuous waveform data morethan two years. The configuration of Hotan Seismic Array is ring-shaped and theaperture is about3km.Hotan Seismic Array has one center site and two rings, threesubstations in the inner-ring with a radius of about600m. Five substations areinstalled in the outer-ring with radius of about1500m. Hotan Seismic Array has9substations with three-component short-period seismometers. Center substation hasinstalled a set of three-component broadband seismometer. Using digital seismicwaveform data recorded by the Hotan Seismic Array, and combining with thewaveform data recorded by Xinjiang digital seismic network, we have done thecomprehensive application research. It involves earthquake location, the phaseidentification from reflection (depth seismic phase) and the application of teleseismicreceiver function method in Hotan Seismic Array. The main conclusions are asfollows:（1） Earthquake location in the south of Xinjiang with the data from sparseseismic network and Hotan Seismic Array dataBy analysing the Hotan Seismic Array waveform data applying broadband f-kanalysis method, we can precisely estimate azimuth and apparent slowness parametersof seismic signal. With Hotan Seismic Array epicenter azimuth parameters, andseismic phase arrival time parameters of Hotan Seismic Array and part stations ofXinjiang regional seismic network, We relocated Yutian Ms7.3earthquake，whichoccureed in Kunlun mountains in the south of Xinjiang, on March21,2008andaftershock sequence with the liner inverse seismic locating method with seismic phasearrival time and azimuth. There are obvious differences between the results ofrelocation and from Xinjiang regional seismic network. The relocation result indicates that the dominant direction of the epicentre distribution of Yutian earthquake sequenceis NS, which is consistent with the surface rupture belt surveyed by field work. Theresult shows that combination of the data recorded by Hotan Seismic Array and partof stations of Xinjiang digital seismic network, may be available to precisely locateearthquakes with a sparse seismic network. It may provide the basic data for thefundamental research and seismic tendency judgement. We also found that applyingreliable azimuth parameters to the earthquake location is efficient and helpful toimprove the location accuracy in the region with unreasonable seismic network layoutor sparse seismic network.（2）Identification the pP or sP phases from reflection wave using Hotan SeismicArray dataThis thesis applied beamforming method with seismic array waveforms data toimprove the SNR of seismic signal. Based on the seismic array beamforming methodand F-Detection algorithm, we applied F-Detection Algorithm to identify pP or sPphases of regional earthquakes and teleseism recorded by the small aperture digitalseismic array in China for the first time. Appling F-Detection algorithm, this thesisidentified pP or sP phases for3earthquakes, whose epicentral distances are22.1°、6.44°、39.62°respectively. The conclusion indicates that applying the_F-DetectionAlgorithm to analyze the Hotan Seismic Array data may be relative accurate inidentifying the pP or sP phases. Accurate identification the pP or sP phases of surfacereflection wave is an effective way to improve the precision of focal depth.（3） The application study of teleseismic receiver function method in HotanSeismic ArrayFirstly, this thesis applies the time domain iterative deconvolution method tocalculate observation receiver functions of9sub-stations (including1set ofbroadband and9sets of short-period seismometers) of Hotan Seismic Array. Secondly,applying H-κ method to analyze observation receiver functions of Hotan SeismicArray, and obtain the crust thickness and Poisson’s ratio beneath Hotan Seismic Array.Finally, using linear inversion method to obtain the S wave velocity structure withinthe depth of100km beneath Hotan Seismic Array. We comparatively analyzed andstudied the observed receiver functions, crust thickness and Poisson’s ratio, and S wave velocity structure beneath each substation of Hotan Seismic Array. The researchresults indicated that taking2.5as the value of the Gaussian filtering factor tocalculate observation receiver function is appropriate for broadband seismic station,and1.5is appropriate for short-period seismic station. Observed receiver functionstudy on each substation of Hotan Seismic Array indicated that the converted waveseismic phase (Ps) at Moho is clear beneath Hotan Seismic Array. The results ofH-κ method indicated that the crust thickness beneath Hotan Seismic Array is53.8km, consistent with previous research result (about55km) form explosion seismicexploration, deep seismic reflection and broadband seismic exploration in the beltsouthwest of Tarim and the west of Kunlun Mountains. The Poisson’s ratio beneathHotan Seismic Array is0.2403. Comparing the results form H-κ method of9sub-stations of Hotan Seismic Array, we concluded that the azimuth coverage ofobservation receiver function is very important to the stability of the results ofH-κ method. S wave velocity structure beneath Hotan Seismic Array shows thatapplying observed receiver function of40T-CMG-1short-period seismometers caninverse the S wave velocity structure within the depth of40km beneath the station.This thesis also studied the crust thickness, crust Poisson ratio and S wavevelocity structure beneath Aksu seismic station, with the same receiver functionmethod in the middle segment of south Tianshan, Xinjiang. The observed receiverfunctions of Hotan Seismic Array and Aksu seismic station are obvious difference,there may be exist double crust or Moho surface is not a sharp discontinuouity, andcomposed of thin layers bunch or transition zone of velocity gradient beneath Aksuseismic station. The crust thickness beneath Aksu seismic station is about45km, andPoisson’s ratio is about0.1922.