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دکترای ژئوفیزیک – زلزله شناسی


غلام جوان دولوئی

مدلسازی معکوس تابع انتقال گیرنده لرزه ای در حوزه زمان و فرکانس و کاربرد آن در مطالعه ساختار پوسته آپسالا، تهران و مشهد

اطلاع از سرعت لرزه ای ساختمان پوسته و جبه بالایی نقش اساسی در فهم بهتر بخش جامد کره زمین دارد. امروزه بکارگیری مدلسازی امواج لرزه ای براساس تکنیکهای پیشرفته مستقیم و معکوس اهمیت زیادی در تعیین ساختار سرعت لرزه ای و ضخامت لایه‌ها در پوسته و جبه بالایی دارد. یکی از اهداف این رساله بررسی تابع انتقال گیرنده لرزه ای در حوزه فرکانس و توسعه و تعمیم این روش با بکارگیری برای ناحیه آپسالا در سوئد می باشد. هدف بعدی این تحقیق بررسی روش تابع انتقال گیرنده لرزه ای در حوزه زمان ومحاسبه ساختار لرزه ای پوسته ناحیه مشهد و تهران بوده است که نتایج قابل توجهی را برای اولین بار در ایران به همراه داشته است.

Transfer/Receiver Functions and Its Application on Crustal Structure of Uppsala, Tehran and Mashhad Areas

BY: Javan G. Doloei
Supervisors: Prof. Dr. M. Ghafory-Ashtiany & Prof. Dr. L. B. Pedersen
Assistant Supervisor: Dr. M. Mokhtari

Ph D. THESIS In SEISMOLOGY

ABSTRACT
The seismic velocity of the crust and uppermost mantle structure plays a key roll to understand the solid Earth. Nowadays, the seismic P-waveform modelling and inversion techniques are advance procedures to derive the seismic velocity and layers thickness within the crust and uppermost mantle. The main aim of this thesis is to investigate crustal structure around seismic stations of Uppsala (UPP, Sweden), Tehran (IR1-IR7, Iran) and Mashhad (MAIO, Iran) based on teleseismic P-waveform modelling and inversion techniques.
The theoretical aspects of Spectral Ratio Transfer Function’s (SRTF) method have been evaluated through numerical investigations of elastic parameters in crustal structure. The SRTF method is developed based on a new inversion technique. Derived SRTF method is applied to 56 teleseismic events, which were recorded at Uppsala station, to estimate an optimum transfer function. A frequency-domain linearised inversion procedure is taken into account to invert P-waveform SRTF to 1-D velocity model. The Moho discontinuity depth for Uppsala station (UPP) is estimated 39km.
Time-domain teleseismic P-waveform receiver function analysis has been used to estimate the main features of the crust and uppermost mantle structure at the Tehran region. Twenty teleseismic earthquakes that were recorded at the seven stations of Iranian Long Period Array (ILPA) were used to calculate radial component and tangential component receiver functions. The results of inverse modelling of teleseismic radial receiver functions has been identified following three major layers beneath ILPA network: the Upper crust has P-wave velocity between 4km/s and 5.8km/s and 14km thickness. The results representing the uppermost crustal structure indicate a strong dependency on the lithology around each station. The middle crust has a positive P-wave velocity gradient from 6km/s to 6.4km/s down to about 30km depth. A P-wave velocity gradient from 6.4km/s to 7.5km/s characterises the lower crust with Moho at 47±۲km at this area. A low velocity mantle, with velocity gradually increasing with depth down to approximately 60km depth has been revealed beneath the South Western of Tehran.
Results of the radial receiver function inversion at the MAIO station (Mashhad Area) showed that (1) the Uppermost crust has a strong positive P-wave velocity gradient from 4 km/s on the surface to 6 km/s at a depth of 7km. (2) The Upper crust contains a thick layer with average P-wave velocity of 6.4 km/s down to 18km depth. (3) The middle crust has a positive P-wave velocity gradient from 6.8km/s at a depth of 18km to 7.5km/s to a depth of about 26km. However, a thin low P-wave velocity layer can be seen at a depth of 27km. (4) Lower crust has a positive P-wave velocity gradient from 7.2km/s at a depth of 38km to 8.0km/s to a depth of about 52km. An unusual high velocity zone in the middle crust has revealed beneath the MAIO station (Mashhad) similar to the ILPA network area (South Western of Tehran Area) that may imply a double crustal thickening