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geology (Fach) / seismic reflection and satellites (Lektion)
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- seismic relfection method general measurement of acoustic impedance contrast between the layers Z, which influences the reflection coefficient - seismic velocity (pwaves) x rock density = Z
- scales of use of seismic reflection 10s of meters for ground water research and enginnering kms for oil exploitations = expensive
- angle of incidence normal angles of incidence have a lower amplitudde and are harder to detect wide angles are a lot easier for detection as the amplitudes are higher
- ray path path from the layer back to the OBS
- general method of seismic reflection ship with airguns sneds out sound waves which travel to the substrate. Different substrates with different densities reflect the waves with different velocities. The waves hit the hydrophones on the chain behind the shhip at different times By this a layered model the desnities can be made
- analysis of the TWT Structurtal = faults, uplifts stratigraphic = Facies , ages Material stays unknown
- boreholes methds boreholes confirm the findings of the seismic relfection by either a) geological logs -bringing substrate to surface and have optical analysis b) geophysical logs: physical measurements are taken underground
- what is an ocean bottom seismometerq OBS is a seismometer that detects man madde and naturall earth motions under water short period OBS: detects high frequencies eg small and short period earthquakes (100x/s) long period OBS: detects broad frequencies relating to large earthquales which are further away from the instrument (10x/s)
- what are wide angle relection methids wide angle reflection uses a wide angle trajectory of the ray path to the vertical -gives information about major variations -gives information about crust and sediment structure (deep to 40m) -produuces model of velocity structre -long range seismic reflection =measures acoustic impedance contrast of layers =shows more details =short range
- what does satellite altimetry measure it measures the sea surface height which gives clue about the seabed below as eg mountains influence the gravitational force which can then be measured on the sea surfce by the radar has a low resolution (depth 2-5km with errors of 200-300m)
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- multi beam sonar echo beams reflect of the seabed high resolution (25-100m with low error 1-2m)
- multi beam sonar echo beams reflect of the seabed high resolution (25-100m with low error 1-2m)
- Turbidites turbidites are caused by gravitational force - sediments from the continental shelfs undergoe big land mass movements and cause turbidite currents perpendicular to the shelf -turbidites are layerd beddings with symmetrical deposition on the left and right side. The grain size decreases from the bottom layer to the top = Downslope ,ass transport
- contorites contorites form due to bottom currents along the continental shelf. They are thick elongated sediment depositions which are instable due to their granular structure and their location near the slope the sediment deposition is assymmetrical and thinnes out the further away from the current