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Line 26: − − [[file:mapping-with-two-dimensional-seismic-data_fig1.png|left|thumb|{{figure number|1}}False structure (dashed lines) created when misties are averaged. Dots show times of events on seismic lines A, X, and N where those lines intersect line Q. Solid lines show true attitude of beds. If dashed events were mapped, false structure would appear.]] − + − [[file:mapping-with-two-dimensional-seismic-data_fig2.png|thumb|{{figure number|2}}(a) Crude base map illustrating seismic line intersections. (b) Table showing misties at seismic line intersections (times in milliseconds). Circled lines constitute a group having small misties. A group can be used as a base to which times on all other lines are adjusted. For example, times on line A561–80 could be shifted down about 52 msec.]]+ + +
Seismic data - mapping with two-dimensional data (view source)
Revision as of 19:02, 24 June 2014
, 19:02, 24 June 2014→Mapping two-way time
Begin mapping by recording the two-way times of the event being mapped for every shotpoint along each line and for all line intersections. The precision of time picks will vary with the scales of lines, but be as precise as possible. The numbers that are recorded are raw times. It is advisable that the times be recorded on a rough draft base map and in tabular form.
Begin mapping by recording the two-way times of the event being mapped for every shotpoint along each line and for all line intersections. The precision of time picks will vary with the scales of lines, but be as precise as possible. The numbers that are recorded are raw times. It is advisable that the times be recorded on a rough draft base map and in tabular form.
In some cases, the distances between the shotpoints printed on the lines are too large for resolving relatively small structures. In this case, it might be necessary to interpolate a ground position and then record a time. However, be aware that a relative position between two shotpoints on a line may not correspond to the same relative position between the same two shotpoints on the basemap. In short, the only ground positions that you can locate accurately on the base map are those that are printed on the base map. If highly accurate intermediate ground positions are important for your interpretation, refer to the person who drafted the map for help or check the field records yourself.
In some cases, the distances between the shotpoints printed on the lines are too large for resolving relatively small structures. In this case, it might be necessary to interpolate a ground position and then record a time. However, be aware that a relative position between two shotpoints on a line may not correspond to the same relative position between the same two shotpoints on the basemap. In short, the only ground positions that you can locate accurately on the base map are those that are printed on the base map. If highly accurate intermediate ground positions are important for your interpretation, refer to the person who drafted the map for help or check the field records yourself.
===Misties===
===Misties===
<gallery mode=packed heights=200px widths=200px>
mapping-with-two-dimensional-seismic-data_fig1.png|{{figure number|1}}False structure (dashed lines) created when misties are averaged. Dots show times of events on seismic lines A, X, and N where those lines intersect line Q. Solid lines show true attitude of beds. If dashed events were mapped, false structure would appear.
mapping-with-two-dimensional-seismic-data_fig2.png|{{figure number|2}}(a) Crude base map illustrating seismic line intersections. (b) Table showing misties at seismic line intersections (times in milliseconds). Circled lines constitute a group having small misties. A group can be used as a base to which times on all other lines are adjusted. For example, times on line A561–80 could be shifted down about 52 msec.
</gallery>
Usually, raw times do not match perfectly at the intersections between two lines. These differences in time are known as misties, and can range in magnitude from 1 msec to tenths of 1 sec. Misties often result between lines that are processed differently, particularly when different datums are chosen for the statics routine. Small misties may also result because normal migration routines cannot compensate perfectly for the geometry of dipping events. Commonly, misties result from “end-of-line” effect, where one line crosses the poorly migrated end of another line. Misties can also arise from errors in the interpretation or in the reading of two-way time.
Usually, raw times do not match perfectly at the intersections between two lines. These differences in time are known as misties, and can range in magnitude from 1 msec to tenths of 1 sec. Misties often result between lines that are processed differently, particularly when different datums are chosen for the statics routine. Small misties may also result because normal migration routines cannot compensate perfectly for the geometry of dipping events. Commonly, misties result from “end-of-line” effect, where one line crosses the poorly migrated end of another line. Misties can also arise from errors in the interpretation or in the reading of two-way time.