| The observation based on large-scale broadband dense array can provide important data for the study of underground media information using seismology methods.Since 2011,the ChinArray project led by the Institute of Geophysics,China Earthquake Administration,together with several domestic units,has carried out ChinArray project in Chinese Mainland step by step.The deployment range of the first phase includes Yunnan and its surrounding areas at the southeastern margin of the north-south elongated band in central part of China,the data used for testing cover a period of 3 yr,from March 2011 to December 2013.The array of the first phase has average station spacing about 30 kilometers and consists of 350 broadband stations.The ChinArray phase I is the first large-scale dense temporary array in China with a horizontal coverage range of 1000 x 1000 km,it is important to conduct a detailed analysis and utilization of the waveforms recorded in ChinArray-1.This article analyzes the azimuth deviation of the seismometer using the teleseismic waveform signals recorded by the ChinArray-I,and attempts to estimate the distribution of sedimentary layers below the station using the teleseismic P-wave signals.Precise three-component records is critical in modern seismic studies,such as inversion of focal mechanism,shear-wave splitting,receiver function and the polarization analysis of Rayleigh-wave.The deployment method,local magnetic anomalies,and incorrect magnetic declination correction will impact the deviation of the seismometer’s north direction from the geographic north,In addition,using observational datas from stations for estimation can improving the reliability and enhance practical value of measurement.We utilized P waves from 696 teleseismic events with epicentral distances ranging from 30°to 90°,and Rayleigh waves from 1928 events with epicentral distances ranging from 10° to 170°recorded in ChinArray-I,based on the polarization characteristics of different waveforms,evaluate and analyze the deviation of the seismometer.Specifically,for P waves,we employed a SNR(Signal-to-Noise Ratio)weighted multi-event method to determine the seismometer orientation.Out of the 352 stations,there were 4 stations that had records of fewer than 10 events and thus were not evaluated.Among the remaining stations,281 stations showed deviations of less than 10°,21 stations had deviations between 10°and 20°,while the remaining stations exhibited significantly larger deviations or experienced instrument failure.Furthermore,independent estimation of the deviation angle was performed using Rayleigh surface wave signals with a period of 20-60 s,we obtained orientation estimates for all 352 stations.Among these stations,272 exhibited deviations of less than 10°,31 stations had deviations between 10° and 20°,and 49 stations experienced significantly larger deviations or instrument failure.It is worth noting that the results obtained from the two methods showed a relatively good consistency,indicating agreement between the orientation estimates derived from the P-and Rayleigh-wave analyses.Using the P-wave and Rayleigh surface wave signals recorded within three years,we estimat-ed the azimuth deviation over time using a series of individual seismic event with high signal-to-noise ratio.We found that 5 stations azimuth changes during the observation period.The results also show that gain faults of different components of the instrument can affect the estimation of azimuth deviation,which is difficult to eliminate through conventional data quality control strateg-ies.The study shows that through Conjoint analysis of azimuth deviation measurement and noise power spectral,the corresponding instrument gain error can be effectively analyzed.The results have reference for the accurate use of data from the ChinArray phase I,and the quality evalution value of related temporary arrays.P-wave polarization analysis can obtain smaller measurement errors,while Rayleigh surface wave polarization analysis uses the azimuth of seismic events for more comprehensive coverage,obtaining more stable results.The converted waves of teleseismic P-waves in sedimentary layers exhibit strong energy in the radial component when sedimentary layer under the station,while causing delays in the travel time of vertical and radial P-wave signals.This article is based on the teleseismic signals recording form the temporary stations deployed by ChinArray I,analyzing the delay of P-waves at various stations,It was found that the vast majority of stations did not observe the delay phenomenon,it may be related to the relatively small observation density of stations in the study area and the lack of a large distribution of thick sedimentary layers.In order to explore an optimized processing method for detecting the distribution of large-scale shallow sedimentary layers based on teleseismic waveforms,it is necessary to conduct more in-depth analysis of relevant research. |
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