Ruhi Saatçılar

A method of ground‐roll elimination

Amplitude‐ and frequency‐modulated wave motion constitute the ground‐roll noise in seismic reflection prospecting. Hence, it is possible to eliminate ground roll by applying one‐dimensional, linear frequency‐modulated matched filters. These filters effectively attenuate the ground‐roll energy without damaging the signal wavelet inside or outside the ground roll’s frequency interval. When the frequency bands of seismic reflections and ground roll overlap, the new filters eliminate the ground roll more effectively than conventional frequency and multichannel filters without affecting the vertical resolution of the seismic data.

Character of active faulting in the North Aegean Sea

Abstract A re-evaluation of the reprocessed seismic reflection data was made for the investigation of the presumed western continuation of the North Anatolian Fault (NAF) in the Aegean and mapping geometries of active faults in the Aegean Sea. Seismic data collected and processed by various national and international companies were selected from the data archives and they were reprocessed after stacking to bring them to the same processing and signal-to-noise ratio standards. The total length of the selected lines is 8000 km. We investigated the character of active faulting in the North Aegean Sea using seismic reflection data. Moreover, the relations of active faults with earthquakes were examined using earthquake fault plane solutions (FPS). We show that the active faults are dominantly normal in character in the NNE Aegean where FPS for earthquakes with M >5 indicate strike-slip movements along these faults. We propose a simple mechanism that potentially explains this inconsistency. Active normal faults are oriented in a NE–SW direction in alignment with the SW escape motion of the Anatolian block in this region and this orientation facilitates instantaneously strike-slip movements along these otherwise normal faults.

The use of the Hartley transform in geophysical applications

The Hartley transform (HT) is an integral transform similar to the Fourier transform (FT). It has most of the characteristics of the FT. Several authors have shown that fast algorithms can be constructed for the fast Hartley transform (FHT) using the same structures as for the fast Fourier transform. However, the HT is a real transform and for this reason, since one complex multiplication requires four real multiplications, the discrete HT (DHT) is computationally faster than the discrete FT (DFT). Consequently, any process requiring the DFT (such as amplitude and phase spectra) can be performed faster by using the DHT. The general properties of the DHT are reviewed first, and then an attempt is made to use the FHT in some seismic data processing techniques such as one‐dimensional filtering, forward seismic modeling, and migration. The experiments show that the Hartley transform is two times faster than the Fourier transform.

Turkey makes major investment in earthquake research

Following the devastating Mw 7.4 Izmit earthquake on 17 August 1999, major state-of-the-art earthquake studies were conducted in the Marmara region of northwestern Turkey. However, other faults with the potential to generate big and potentially devastating earthquakes occur in a variety of different tectonic regimes in Turkey, and these faults and regions have not received similar attention. For example, the East Anatolian Fault (EAF) is influenced by the convergence of the Arabian and Anatolian plates along the Zagros-Bitlis suture zone. Faults in the Aegean Extensional Province (AEP) are purely normal faults. The main faults in the Marmara region occur within both transtensional and transpressional domains (locations are shown in Figure I). All of these regions pose seismic hazards and also require focused study.

The lattice filter in ground‐roll suppression

Seismic reflections are sometimes masked by Ray‐leigh‐type surface waves that are termed ground roll in seismic literature. An adaptive lattice filter is used to recover reflected signals contaminated by ground roll. Experiments on synthetic and field data showed that the adaptive lattice filter technique is very effective in ground‐roll elimination. In addition, the filter works as a whitening operator, compresses the signal, and increases the signal‐to‐noise ratio.

An environmentally-friendly integrated seismic imaging for coal exploration in the Miocene Soma Basin, Western Turkey

Seismic reflection data from target depths of several hundred metres have been acquired and processed as an aid for lignite exploration in the Miocene Soma Basin, western Turkey. An environmentally-friendly approach was followed by acquiring the data with mini-vibroseisseismic source along crooked lines, using available mountain/forest and village roads; quality control tests were conducted to determine optimal field parameters that would yield dataset with best signal-to-noise (SN) ratio prior to real data acquisition; and stratigraphic interfaces giving rise to reflection events in the seismic data were identified from the vertical seismic profiling (VSP). Stacked seismic sections were successfully correlated with geological cross-sections drawn based on available borehole data. Thus, it is shown that decreasing time and the cost for coal exploration is possible by utilising surface and VSP. Environment friendly approach of the seismic method applied in this study is also beneficial in regard to environmental concerns.

Recursive Q‐filter design and its application to seismic data

A recursive Q-filter (RQF) method has been developed in order to generate synthetic seismograms including attenuation or to remove attenuation effect from seismic data. This method can be applied both in the Fourier or in the Hartley domain. The RQF impulse response is also compared to the analytical result given by Kjartansson (1979). The design of the RQF method in case of time dependent or frequency dependent (scattering Q) quality factor are illustrated using synthetic and real data sets.

Integration of walkaway VSP and surface seismic reflection data for coal exploration in Soma Tertiary Basin, Turkey

Summary Soma Tertiary basin is one of the most important region for exploration and production of coal and has a big potential for the production of coalbed methane. Integrated seismic reflection studies includes multichannel seismic reflection survey and 3C-WVSP survey to develop efficient methodology for exploration of coal and coalbed methane on various coal basins in Turkey. The goal of this paper is to explain the 3CWVSP data acquisition and data processing. Velocity information derived from the VSP shot records was used to convert surface seismic time sections to depth sections. Results showed high compatibility with the drilling logs along the seismic lines. The corridor stack of VSP is highly compatible with surface seismic reflection sections.

Reply by the authors to B. Zhou

The algorithm for fast computation of numerical derivatives using real FFT is a brilliant idea. Due to the halving, it is certainly possible to compute the derivatives of real signals almost twice as fast as the conventional procedure. However, we do not agree with Zhou about the achievement of the same performance of the fast Hartley transform.