Three-dimensional Q Tomography

The quality factor Q-value is a reflection of earth’s internal substance of thecomposition, crystal structure, states of matter, temperature and material flow ofimportant information, and is also one of the main parameters for describing thecharacteristics of the earth media. The Q-value research is one of the most importantway to study the earth’s internal structure and its dynamic system.The study area of this thesis is the southeast of Gansu province and adjacent areas.We use great numerous micro-seismic waveform records from the Gandongnanportable seismic array. We obtain phases waveform of Pg and Sg by using of phaseidentification. We handled3273earthquakes,65486P and57839S seismic phases.The total Q-value was calculated on the earthquake-station path. With the totalQ-value as observation value, combined with ray tracing to obtain the3-D blockmodels T-matrix.Damped least square method for3-D inversion calculation ofQ-value, and then we can get the3-D Q-value structure of different frequencyp-waves and s-waves. Above the25km depth, the rays number is more than5in themost of region, and distinguish better. During the whole Q-value calculation process,we rigorously eliminate the effect of geometric attenuation coefficient, reflection andtransmission coefficients and the0of source function. This method is strict tocalculate the Q-value by P-wave. We use the Nakamura method to calculate the siteresponse of Q-value calculation by S-waves.The results show that:1.Q-value distribution: The top of the lower crust (about25km) Diebu the vicinity of the Q-value is relatively low. The low Q-valuedistribution east or northeast shallow extension, forming the Alice tongue, this isconsistent with the “Channel-flow” point of view. The Q-value distribution isdifferent on both sides of Xiqinlingbeiyuan fracture. It shows the changes in seismicwaves through the fracture. Within10km-25km depth, south of local area WushanQ-value is relatively low. It maybe due to the area distribution of the upwelling hotmaterial from the crust-mantle. The Q-value of Guangyuan-Qingchuan area isrelatively low because of the frequent seismic activity.2. Seismic depth and Q-valuedistribution: The Q-values distribution on both sides of the most earthquake strips are different. The most regions that Q-value is relatively low or sudden change areearthquake-intensive.3. Profile velocity and Q-value distribution: They have aconsistent distribution pattern. Velocity where there are obvious differences, Q valuedifferences are also apparent. Further notes the Q-value and speed are reflection of thedeep structure.The innovation and research results:1. Improved the calculation method aboutQ-value, increasing its calculation accuracy. And we computer program about thismethod.2. We firstly obtained the Gandongnan region’s3-D Q-value structure of Pand S waves with the portable seismic array observation data.