METHOD AND SYSTEM FOR AUTOMATIC SEISMIC REFLECTION PICKING

摘要

1,219,823. Seismic signal processing. TEXAS INSTRUMENTS Inc. 30 April, 1968 [13 June, 1967], No. 20378/68. Heading H4D. A system is provided for selecting automatically those seismic events which can be followed from one trace to an adjacent trace of a seismogram. Field procedure.-Shots are fired into the centres of geophone spreads at a plurality of points along a traverse to provide a set of multi-trace seismograms digitally recorded on magnetic tape. Signal processing.-The field records are played back, subjected to static and normal moveout error corrections, then stored on a drum from which they are fed to a unit which produces a spike signal for each peak (or trough) on the traces. The spike signals represent seismic " events " and are stored on a further drum. Events are followed from trace to trace by selecting an event at time t I-1 on one trace I - 1 and looking for it on the adjacent trace I in a time gate which is centred on the estimated event time t 1 and which has a width 2# proportional to the mean separation of the spike signals for trace I in the time zone concerned. If more than one event is found in the search, the one nearest to the estimated time is selected. If no event is found the event t I-1 is rejected as spurious. The time t I of an event found and the time t I-1 are used to estimate the event time for the next trace I + 1 and a similar search is made on trace I + 1. If an event is found, the event time t I+1 and the times t I , t I-1 are used to estimate, on a least mean squares fit basis, the event time on the next trace. This search procedure is repeated on further traces until the event can no longer be followed, then searches are made for other events occurring on two or more traces. Events thus found are allotted " grades " G; equal to n#A i , where n is the number of traces across which an event i can be followed and #A i is the mean amplitude of the event i spike signals across those traces. This particular grading rates weak events occurring across a large number of traces as significant as strong events occurring across a few traces. An average value A, of the amplitudes of all events occurring on all traces within a selected time zone is derived and used as a threshold value in the plotting of graded seismograms. Such seismograms are produced by emphasizing or plotting only those events whose individual grades G i exceed the product X.A r , where X is a factor which can be varied to produce different graded displays, e.g. if X is large only strong events will be emphasized or plotted. A r is a function of record time and takes into account the increasing attenuation of seismic signal amplitude with record time. The signal processing may be done by digital computer and a flow chart for such processing is given.