sedikit excerpt tentang teorinya bagi yg tertarik: The downgoing wavefield in VSP data provides a direct observation of the changing nature of the seismic source wavelet as it propagates through the earth, and is an ideal dataset for the study of seismic attenuation. A Spectral Ratio method was used to estimate the Q factor. This method is based on the assumption that the logarithm of the amplitude of a seismic wave decays at a rate approximately proportional to the frequency, and that the attenuation is independent of frequency. Q is then estimated using the following formula: Ln (Ai (Zi,f)/Ao(Zo,f)) = C - πDtf/Q.
Where Ao and Ai are the Fourier amplitude spectra of a reference trace and another trace of interest at depths Zo and Zi respectively, f is the frequency, t is the one-way arrival time difference between the two receiver depths, C is a constant which takes into account the source function, receiver function, geometric spreading and coupling factor, Q is a measure of the attenuation occurring between the depths Zo and Zi. A least-squares linear regression of the left-hand side of the equation versus frequency yields a slope b = -πt/Q. The spectral ratio method assumes that the source waveform and geophone coupling are the same at all receiver levels, and geometric spreading is frequency independent. In a practical sense, the accuracy of the estimated Q also depends on the methods of trace analysis windowing, spectral analysis, and least squares line fitting. ----- Original Message ---- From: Herry Maulana <[EMAIL PROTECTED]> To: iagi-net@iagi.or.id Sent: Monday, 28 May, 2007 1:56:48 PM Subject: Re: [iagi-net-l] Nanya VSP iya mas, dipakai umumnya untuk mempelajari attenuation, jadi bisa dipakai untuk mengestimasi Q factor. Maaf detil pengerjaanya kurang tahu, tapi kita pake VSFusion untuk processing dan Q estimation. Sependek yg saya tahu, uncertainty dalam Q estimation ini akan tetap ada (depth and formation related) sedangkan Q compensation yg akan digunakan dalam seismic processing cuma 1 number (biasanya diambil angka rata-rata estimasi Q dari VSP), cmiiw. Salam, Herry ----- Original Message ---- From: Leonard Lisapaly <[EMAIL PROTECTED]> To: iagi-net@iagi.or.id Sent: Monday, 28 May, 2007 12:00:53 PM Subject: RE: [iagi-net-l] Nanya VSP Mungkin downgoing wave-nya bisa dipakai untuk estimasi Q yang nantinya dapat digunakan untuk Q compensation di processing? LL -----Original Message----- From: Paulus Tangke Allo [mailto:[EMAIL PROTECTED] Sent: Sunday, May 27, 2007 1:37 PM To: iagi-net@iagi.or.id Subject: Re: [iagi-net-l] Nanya VSP yaps saya setuju. posting saya sebelumnya, karena belum pernah saya lihat penggunaan koefisien transmisi dalam processing VSP. selain itu, saya pribadi, lebih mudah membayangkan koefisien refleksi ketimbang koefisien transmisi. apa memang sudah pernah ada yang menggunakan informasi koefisien transmisi ini setelah running VSP? --pta On 5/25/07, Leonard Lisapaly <[EMAIL PROTECTED]> wrote: > > > Mestinya downgoing primary membawa informasi mengenai lapisan di atas > geophone, tapi dalam bentuk transmisi, bukan refleksi. > > Informasi dari seismik bisa diambil misalnya dari waktu dan amplitudo > seismik. Karena dalam VSP informasi utamanya adalah waktu, dan adalah penting > mengeliminir noise koheren dari multipel, maka tetap direct arrival ini bisa > dimanfaatkan. > > LL ---------------------------------------------------------------------------- Hot News!!! CALL FOR PAPERS: send your abstract by 30 March 2007 to [EMAIL PROTECTED] Joint Convention Bali 2007 - The 32nd HAGI, the 36th IAGI, and the 29th IATMI Annual Convention and Exhibition, Bali Convention Center, 13-16 November 2007 ---------------------------------------------------------------------------- To unsubscribe, send email to: iagi-net-unsubscribe[at]iagi.or.id To subscribe, send email to: iagi-net-subscribe[at]iagi.or.id Visit IAGI Website: http://iagi.or.id Pembayaran iuran anggota ditujukan ke: Bank Mandiri Cab. Wisma Alia Jakarta No. Rek: 123 0085005314 Atas nama: Ikatan Ahli Geologi Indonesia (IAGI) Bank BCA KCP. Manara Mulia No. Rekening: 255-1088580 A/n: Shinta Damayanti IAGI-net Archive 1: http://www.mail-archive.com/iagi-net%40iagi.or.id/ IAGI-net Archive 2: http://groups.yahoo.com/group/iagi --------------------------------------------------------------------- ---------------------------------------------------------------------------- Hot News!!! CALL FOR PAPERS: send your abstract by 30 March 2007 to [EMAIL PROTECTED] Joint Convention Bali 2007 - The 32nd HAGI, the 36th IAGI, and the 29th IATMI Annual Convention and Exhibition, Bali Convention Center, 13-16 November 2007 ---------------------------------------------------------------------------- To unsubscribe, send email to: iagi-net-unsubscribe[at]iagi.or.id To subscribe, send email to: iagi-net-subscribe[at]iagi.or.id Visit IAGI Website: http://iagi.or.id Pembayaran iuran anggota ditujukan ke: Bank Mandiri Cab. Wisma Alia Jakarta No. Rek: 123 0085005314 Atas nama: Ikatan Ahli Geologi Indonesia (IAGI) Bank BCA KCP. Manara Mulia No. Rekening: 255-1088580 A/n: Shinta Damayanti IAGI-net Archive 1: http://www.mail-archive.com/iagi-net%40iagi.or.id/ IAGI-net Archive 2: http://groups.yahoo.com/group/iagi --------------------------------------------------------------------- Yahoo! Answers - Got a question? Someone out there knows the answer. Try it now. ___________________________________________________________ Now you can scan emails quickly with a reading pane. Get the new Yahoo! Mail. http://uk.docs.yahoo.com/nowyoucan.html
