Interferometric OBS imaging for wide-angle seismic data

Abstract

Marine wide-angle seismic data obtained using air guns and ocean-bottom seismographs (OBSs) are effective for determining large-scale subseafloor seismic velocities, but they are ineffective for imaging details of shallow seismic reflection structures because of poor illumination. Surface-related multiple reflections offer the potential to enlarge the OBS data illumination area. We have developed a new seismic imaging method for OBS surveys applying seismic interferometry, a technique that uses surface-related multiples similarly to mirror imaging. Seismic interferometry can use higher order multiple reflections than mirror imaging, which mainly uses first-order multiple reflections. A salient advantage of interferometric OBS imaging over mirror imaging is that it requires only single-component data, whereas mirror imaging requires vertical geophone and hydrophone components to separate upgoing and downgoing wavefields. We applied interferometric OBS imaging to actual 175 km long wide-angle OBS data acquired in the Nankai Trough subduction zone. We obtained clear continuous reflection images in the deep and shallow parts including the seafloor from the OBS data acquired with large spacing. Deconvolution interferometry is more suitable than correlation interferometry to improve spatial resolution because of the effects of spectral division when applied to common receiver gathers. We examined the imaging result dependence on data acquisition and processing parameters considering the data quality and target depth. An air-gun-to-OBS distance of up to 50 km and a record length of 80 s were necessary for better imaging. In addition, our decimation tests confirmed that denser OBS spacing yielded better quality and higher resolution images. Understanding crosstalk effects due to the acquisition setting will be useful to optimize methods for eliminating them. Interferometric OBS imaging merged with conventional primary reflection imaging is a powerful method for revealing crustal structures.

Seismic reflection imaging of deep crustal structures via reverse time migration using offshore wide-angle seismic data on the eastern margin of the Sea of Japan

“…On the other hand, imaging shallow structures, such as sedimentary layers in the Yamato Basin and deformations of the fault-fold belt in the Sado Ridge to the Mogami Trough (Sato et al 2014), is difficult by using only primary reflections because of spatial aliasing of migrated reflections from wide-spacing OBSs (e.g., Zelt et al 1998). RTM with surface-related multiples (e.g., Grion et al 2007;Liu et al 2011;Shiraishi et al 2017Shiraishi et al , 2019 could be useful for imaging internal structures of the thick crust and sedimentary layers. Updating velocity models by waveform inversion involving reflection phases may also be helpful for further improvement of the reflection profiles (e.g., Sirgue et al 2010;Shiraishi et al 2019) with better spatial resolution and reliability of velocities within the thick crust than that by traveltime tomography, especially in the thick crust with the shallow complex fault-fold belt (the eastern side of Figs.…”

“…To overcome these problems, subsurface imaging by directly using reflections recorded in airgun-OBS data is important. In most cases of crustal-scale seismic exploration using OBSs with wide spacings of more than a few kilometres, not only reflection imaging by using primary reflections (Dessa et al 2004;Qin et al 2020) but also using multiple reflections by mirror imaging (Grion et al 2007) and interferometric imaging (Shiraishi et al 2017) are useful methods for obtaining reflection profiles, including shallow subsurface profiles, from nondense OBS data to better understand crustal structures in addition to detailed profiles by MCS surveys.…”

Structure and mechanics of the subducted Gorda plate: constrained by afterslip simulations and scattered seismic waves

“…These methods can be used to retrieve body waves and generate reflection images of the subsurface. They has already been used to retrieve body waves using dense array in both local scale (Nakata et al, 2015) and global scale (Poli et al, 2012), with a few attempts in subduction zone environments (Ito and Shiomi, 2012;Tonegawa et al, 2015;Shiraishi et al, 2017).…”

Application of deconvolution interferometry to receiver ghost reflection in vertical cable seismic survey

“…Despite all this, ghost reflections can be used for sea surface imaging to improve the resolution of marine seismic data (Laws & Kragh, 2002;Orji et al, 2010). If the receiver is deployed at adequate depths so that receiver ghost reflections can be distinguished from primaries, ghosts imaging come true, such as ocean-bottom seismometer (Dash et al, 2009;Wang et al, 2012;Shiraishi et al, 2017) and vertical cable seismic (VCS) (Hondori et al, 2019;Wang et al, 2019;Chen et al, 2022;Wang et al, 2022).…”