Pacific Coastal & Marine Science Center
Coastal and Marine Earthquake Studies
|Central California/San Francisco Bay Earthquake Hazards Project, 1998
Common Midpoint Method
The MCS method derives its benefits from data redundancy and multiple raypaths. The diagram shows four successive shots along a survey line, and the resulting raypaths for reflections from the seafloor. At each shot, a reflection from a common mid point on the seafloor is recorded on increasingly further channels. The increasing travel times can be corrected for geometrically, and the resulting traces stacked together with a resultant increase of signal to noise proportional to the square root of the number of traces stacked, also refered to as the fold. The MCS method also improves the lateral resolution. Note that the CMP distance is half of the distance between channels, and independent of the shot interval. The MCS data from the San Francisco Bay was collected with a 6.25 meter channel spacing, resulting in CMP's that are 3-1/8 meters apart. The shot interval varies between 6.25 and 12.5 meters, but that affects only the resulting fold.
Conventional MCS (research)