Marine 2D and 3D Reflection Seismics

Reflection seismics are a common tool to explore the seafloor and deeper geological structures. This method takes advantage out of situation that acoustic waves are reflected at geological interfaces. 2D reflection seismics enable us to produce geological cross sections.

The marine 2D-Reflection seismic method produces seismic images of geological structures from reflected acoustic waves. Commonly air guns are used as seismic signal source. Dependent on the geophysical task one can use single airguns or arrays of more guns. The seismic signals will be reflected from geological interfaces back to the sea surface. In order to detect and record the reflected waves a seismic cable (so-called “streamer”) with a length of up to 4000 meters will be towed behind the research-vessel. This setup enables us to cover every subbottom point multiple times. This multiple coverage improves the signal to noise ration significantly. Further, it enables the determination of the seismic sound velocity.

Fig.1: Ray path of seismic signals within a sketch and a data example from the eastern Mediterranean. It shows a cross section of the Eratosthenes Seamount and the Levant Basin Source: BGR

Figure 1 shows the ray path of seismic signals within a sketch and a data example from the eastern Mediterranean. It shows a cross section of the Eratosthenes Seamount and the Levant Basin. It was possible to resolve sediment horizons up to 12 km depth.

Fig.2: Selected steps of the data processing sequence from a single shot gather (A) and seismic velocity analysis (B) to the final stacked and migrated seismic image (C) Source: BGR

Figure 2 shows selected steps of the data processing sequence from a single shot gather (A) and seismic velocity analysis (B) to the final stacked and migrated seismic image (C).

Marine 3D-Reflection Seismics

The marine 2D reflection seismics is only able to image a cross section of the underlying geology. In order to image all three dimensions of the geology it is necessary to acquire 3D reflection seismic data. In comparison to 2D reflection seismic data acquisition 3D reflection seismic data acquisition uses several seismic sources and seismic cables (please compare Fig. 3 and Fig. 4). BGR develops since 2010 a mobile 3D reflection seismic data acquisition system that can be mobilized on different research vessels. The 3D reflection seismic data acquisition requires higher precision and a dense seismic line grid. The survey of a 10 km by 10 km area (100 km²) needs approximately 3 weeks. This is why we usually do a 2D seismic pre-site survey in order to locate the precise target area followed by a 3D survey. Video documentations of test surveys of our 3D seismic system aboard the research vessels METEOR and SONNE are provided by the links.

Fig.3: (A) Sketch of a 2D reflection seismic setup. (B) Implementation aboard the research vessel Source: BGR

Fig. 4: (A) Sketch of a 2D reflection seismic setup. (B) Implementation aboard the research vessel Source: BGR