Seismic Reflection Lab, Offshore California


What is the water depth in these profiles?  How can you compute this, and does it match what the records show?

Compare the thickness of the Miocene (Tm) in the MSCH-1 with the other holes in Figure 3B of Bohannon and Geist (1998, GSAB).  Using the sound velocity profile measured in OCS-CAL 75-50 (Figure 3A, Bohannon and Geist (1998, GSAB)), estimate the TWTT that you would expect for the Miocene rocks in MSCH-1 on the four seismic lines that surround it.  What assumptions do you have to make about this?

What is the maximum depth in the rock shown on the four seismic profiles, and what assumptions do you have to make to answer this question?

On line 103, what happens at about shot point 1250?

On line 102, what happens at about shot point 1320?

Do you see evidence for the basalt flows seen in Figure 3A OCS-CAL 75-70 in these seismic profiles?  What would you be looking for?  Was it found in MSCH-1?

How well do the four intersections of lines correspond, and how do they help you to see the 3D structure in this area? What reflections can you match on each line where they intersect, and how are those reflections dipping? 

What is the dominant fault type in this area?  Does it match the plate tectonic setting?

Navigation map extract, showing the four lines we have (green highlight on map to left).

Fig. 2 of  Bohannon and Geist (1998, GSAB) shows the location of a series of drill holes, including #8, the MSCH-1.  Figure 3B  shows the thicknesses of the rock units in the holes, and Figure 3A the velocity profile from one (OCS-CAL 75-70).  There are links to this paper on the course syllabus.


The Mobil San Clemente core hole No. 1 (MSCH–1)  was spudded on the shelf in the middle of the 4 seismic lines, and penetrated (Crouch and Suppe, 1993).

  • 930 m of upper Miocene sandstone and shale,
  • 480 m of the middle Miocene Monterey Formation
  • 430 m of the early Miocene San Onofre Breccia
  • Total 1840 m (6037 feet)

Review Labs introduction.

Background Data Opened via File, Geology labs, California Offshore

Faults and earthquakes

  • Filter both the focal mechanisms and the regional faults to show just the region of this map.  Use Map query, and   Rectangular region or Current map area.
  • Color code by string field using "SLIPSENSE" for the faults.
  • Plot the beach balls for the focal mechanisms.
  • Frequency table will give a count.


Create a 3D fence diagram in Paint
  • Use Extracts of the 4 lines, or
    • Show seismic line at defined zoom level in Adobe  (must be the same for both lines)
  • Find the intersection with the second line (“crossover”) , shown along the top margin.

  • Screen capture into Paint
  • Cut at the crossover
  • Repeat for the second line, in a second Paint window
  • Skew the two images (Image, Stretch/Skew), about 30 for a starting value, one positive and the other negative
  • Paste the two images together in Paint
    The reflections should match in the two lines, and you should be able to see the dip of the bedding.

Last revision  1/28/2017