An Integrated Marine Seismic Approach for Time Efficient High-Resolution Surveys
Authors: Huebscher C. , Spiess V. 
Published: October 2008

At Bremen University we designed an integrated seismoacoustic survey concept for marine environmental surveys. Several seismoacoustic measurements in different source frequency ranges are carried out simultaneously. Hullmounted Hydrosweep multibeam sounders (15.5 kHz) and ultra high-resolution digital narrow beam Parasound echosounder (2.5-5.5 kHz) are available on German research vessels. For multichannel seismics we designed a streamer with a flexibel spatial response function, which can recieve seismic signals from deep penetrating, low-frequency sources as well as high-frequency sources like waterguns (&gt; 1500 Hz). A single seismograph records different, alternating released seismic sources with recording parameters, which change from shot to shot and source to source, respectively.

At the University of Bremen we designed an integrated seismo-acoustic survey concept for high-resolution marine environmental surveys. Several seismoacoustic data sets are collected in different source frequency ranges. Hull-mounted Hydrosweep multibeam sounders (15.5 kHz) and ultra high-resolution digital narrow beam Parasound/ParaDigMa echosounder (2.5-5.5 kHz) are available on German research vessels. For multichannel seismics a streamer design was chosen to allow the adaption of the spatial response function of the hydrophon groups to seismic signals from deep penetrating, low-frequency sources as well as from high frequency sources like waterguns (&gt; 1500 Hz). A single seismograph records the different, alternating released seismic sources with recording parameters, which change from shot to shot and source to source, respectively.

Introduction

Marine sedimentary deposits provide high-resolution historical record of the Earth's atmosphere, hydrosphere and cryosphere. Understanding the sedimentary processes and structures may enable us to unravel the basic relationships and characteristics. Therefore, since three decades the marine environment isinvestigated with a variety of geophysical and geological methods, specifically for seismic and sediment sampling. Seismis profiling measurements with multi-channel seismics or swath sounding elucidate spatial structures of the seafloor and the sedimentary structures beneath. The integratedinterpretation of core analysis and cross-sections allows to extrapolate sedimentological information and provides insight into the structural framework of core sites.

Modem studies of the Earth System and its variability require investigations of 4th order cyclic climate variations (periodicity of 103＿104 years), which correspond to changes inphysical properties of sediment cores on a scale of meters to some 10 cm. It is chiefly the seismic method that reveals structural information about sedimentary layers. However, most of the conventional marine seismic equipment has been developed for investigating hydrocarbon reservoirs. Thus, due to the wavelength of more than 10m vertical resolution of the industrial gear is oftenly not sufficient for the above discussed purposes. On the other hand, high-resolution marine seismic systems with an appropriate resolution reveal no or little information about the tectonic framework of fine-scale depositional processes and related structures due to the lack of deep signal penetration. The trade-off between vertical resolution and penetration depth represents an important restriction for optimized data acquisition.