Has it really been four weeks? I have been processing data and suddenly my last day is tomorrow. When I first looked at my source gathers I was amazed at how clear it was and how many hyperbolas it had. (I need hyperbolas for a reflection survey) But they soon became very dirty.

Here you can see shot gathers from positions 1, 37, and 74. The lable bars refer to these numbers as FFN 1001, 1037, and 1074.(FFN stands for field file number) The vibe started at the south point of the line at position one and moved north. Later in the morning, when the vibe was at shot point 16, the wind picked up and started to rattle all of the pin flags that we had the shot points marked with. I wanted to go behind the vibe and pull out all the pin flags that we didn't need anymore so at least the left half of the data would be clean. But Sandra wouldn't let me because she wanted me to learn how to deal with bad data.

I used Adobe Illustrator to finish up the maps for my poster. I have marked where source gathers above were taken in this figure. They are labled s1, s37, and s74.

Sandra bulk shifted the seismic file and then I used SPW to kill the pilot channel at 24, make a cmp (common midpoint) velocity semblance, pick velocities with the semblance, pick early and tail mutes, make a cmp stack, apply residual static shifts, and deconvolute the stack. I had problems with my semblance so I ended up revising and repicking for quite a few days. In the end all of the noise from the pin flags did not show up in my final stack so I did not need to use any filters.

Now that I have the data processed I am working on the interpretation. I am comparing my stack with the stack from a line parallel to mine on the other side of the fault. Hopefully, since this is a strike-slip fault, I will be able to find underground features, such as channels, that match in both lines and then figure out the lateral displacement of the fault by measuring the distance the same feature is offset in the other stack. These are some possibilities I have come up with so far:

My line is Line 2. Since the fault between the lines is right lateral, features in Line 3 should be further right in Line 2 by the way I have them set up. The reason that I am looking for the displacement of the fault is because it indicates how active the fault is. Faults with larger displacement are more likely capable of a strong earthquake.

    Last week I went out to the field with a team to run a seismic survey.  I had to get up at 4 am each morning because we had to get the survey done before it was too hot.  We started out by throwing out geophones every five meters and then we layed out cables to connect the geophones and geodes.  When all was set up right the Vibroseis would start at one end of the line and "vibe" three times at intervals of ten meters.  Because we were using a vibroseis instead of a hammer we had to put the survey lines along roads, and some of them were not very straight.  While the vibe was moving along, I used a Trimble GPS to record positions of the geophones and the squashed circles made by the vibe.

  I downloaded the points and put them on this map in ArcGIS.

    For my project I will analyze the red line.  It is nice and straight because it was on a flat place with no vegetation.  The line had about 144 geophones at 5m spacing so it was 720 meters long.  If you notice there are some pink dots extending south of the red dots.  These are where we vibed beyond the geophones to get every last bit of data out of the line.  Where ever possible we tried to extend the lines and shot points so that the four lines could overlap like a tic tac toe board.  The whole project aims to find where a strike slip fault is and see how far it has moved.

    We think that the strike slip fault runs along the tree line which you can see as black spots in the aerial photo.   The two east-west lines that cross the tree line should find the fault because they are perpendicular to it.  My line and the other north-south line will not detect the fault but will hopefully find some underground features that can be compared to see how much displacement the fault has caused.  

    Overall the field work was a lot of fun.  One of the land owners rescued wolves and coyotes and kept them in with a big fence.  Every morning they would all howl at dawn for about a minute.  And one morning it rained.  It was short but it was the only rain I have seen since May.  Lots of things broke or would not work so the first few days we had to stay late in the afternoon when it was hot.  The vibe popped three air bladders and leaked hydrolic fluid.  Fortunately Sandra was able to fix it every time.

Next week I will start processing the data with SPW. 

I can’t believe almost four weeks have gone by already. This week I am starting to learn seismic software. I am going through SPW tutorials every morning. Though I know how to use them, I am still having trouble comprehending colorful semblance plots. I also need to better understand how the Common Midpoints come together in a siesmic reflection survey.

Next week I was supposed to go out to the field to survey, but we could not get the permits in time. Hopefully it will happen the week after that. I am also learning how to use a Trimble, which is a big fancy GPS that makes funny noises. I will take points with the GPS to import into a map on arcGIS. My skills with arcGIS have improved allot. The hardest part now is finding free data on the internet. I had the same problem when I was looking up phone numbers for the owners of the land we will survey on. There were plenty of websites that could do just what I needed for $20 to $40, but I spent hours trying to find the information for free.

I finally went to the Las Vegas strip. Unfortunately nothing interesting happened. You really need to waste a hundred dollars in order to enjoy the strip. Then I went to the Kelso sand dunes in Mohave National Preserve. They were neat because the sand would make a rumbly humming noise when I got allot of sand to start sliding down the dune. It is a somewhat rare phenomenon that happens at only 30 sand dunes in the world.

A view of the Las Vegas strip from Red Rock Canyon.

A view of Death Valley from Golden Canyon

Some normal fault scarps in Death Valley

On top of a ridge at Lake Mead.

Sandstone from Jurassic sand dunes at Lake Mead.

I finally figured out arcGIS and made a map in time for us to scout out a survey location in the town of Pahrump NV. On Friday Sandra, I, and some geologists drove out to a near by valley where there is a right-lateral strike slip fault. Strike slip faults are significantly harder to see than normal faults because they don't have a scarp. In addition, my arcGIS map was no help because I found several different fault maps on the USGS website that each disagreed on the position of the fault by at least 350 meters.

The best clue that we found was a wash that jagged off course for a ways and then continued as if it had followed the fault line. There were also a lines of trees and shrubs that suggested fault lines. There is something about the fracture at a fault line holding more water. We also noticed that the ground was bumpy due to distortion in the fault area.

The next step will be to get permission from the people living in the valley to conduct the survey. Cathy has now notified me that this was three years ago but the engineering department got in trouble because they ran the vibrosize near the physics building and misaligned all of their lasers. We also want permission to dig a ten foot deep trench. Hopefully it will show exactly where the fault is and give us a better idea of how to interpret the data when we run lines of geophones. We plan to get permission by telephone. Supposedly there are drug operations in the area and it is common for locals to pull shotguns on strangers.

I took the weekend of and went hiking at Lake Mead. There was even more Jurassic sandstone. I can't complain because it weathers into all sorts of cool formations that are fun to climb on. Then I went to a lava field. I found a lot of large calcite crystals, most seemed to have formed around bubbles in the lava. Hopefully someday I will remember to bring may camera connector so I can post some pictures.