Study On Three-dimensional Q Value In The Southeast Of Gansu Province

Seismic wave attenuation property is an important issue in seismology. Thereexists an important impact factor in seismic wave propagation path effects (seismicwave attenuation) besides the geometric attenuation with distance. It is the nonelasticmedium attenuation which measured by the quality factor Q. Value Q is one of thebasic physical parameters in the earth medium. Through the study of seismic waveattenuation Q, it can be further understood that the characteristics of the interior of theearth medium, thermodynamic state and the composition and changes of the internalstructure of the earth. Studying value Q is one of the main research direction ofseismology.Southeast of Gansu Province in the northeastern margin of Qinghai-Tibet blockis located in the composite parts of Qilian Mountains seismic belt and the North-Southseismic belt which controlled by force of India plate northward collision with Eurasia,and it is effected by relatively stable Alashan block, Erdos block. The zone is atectonic activity and sensitive stress field area where occurs frequent active fault zoneseismic activity and several medium-strong earthquake took place in the history. Overthe years the area has always been one of the hot areas of the research scientist.Effective time interval of research data is beginning from the November13,2009to November30,2011and the study area (N32.2°-36.0°, E102.7°-107.1°) maintains176seismic stations (150Broadband Stations,26fixed stations). By the phaseanalysis and initial positioning,11051recorded regional seismic events are receivedas the basis of grid search. With the earthquake location method these earthquakeswere relocated, and more than3(including3) seismic events are received recorded for8158; Then by waveform interception and waveform recording of these seismicevents, different seismic stations were calculated the total value Q (phase from thesource to the station on the path). Through the three-dimensional ray tracingcalculation, T time matrix with a total value of Q as the observed value and by meansof damping least square algorithm inversion calculation, the3D Q wave of differentfrequency value structure is obtained. Nakamura method should also be used tocalculate a large number of records, waveform. The1-20Hz site response spectrumsof176stations are obtained.Main progress of the paper is shown as follow:1.8158seismic events with168439P wave seismic phase record and148367theS wave records of in the three dimensional Q value inversion data is the mostabundant data recording station density in one of the biggest flow array records. Byusing these data, the accuracy of P wave and S wave3D Q structure is given.2.3D value Q calculation method is improved. The improved method in thecalculation of the process eliminates the influence of geometric attenuation coefficient,source maximum displacement spectrum value parameter on the Q calculating andincreases the precision of value Q calculation. It is an important innovation of thispaper.3. There is obvious difference of Q in the large fault, geological boundaries of the deep, shallow area. The stronger region, the more obvious difference of Q value isobserved.4. The amplification effect of flow station site response spectrum is much moreobvious than the fixed station site response spectrum has obvious. Fixed stations arelocated in the bedrock and on the other way flow station are mostly in the soil. It isproved that the soil has great effect on the seismic wave.