I really wanted to thank IRIS for this experience.  As a result of my internship I have decided to become a Ph.D. student at the University of Wyoming.  I am working in the marine seismology group under Professor Steven Holbrook.  To start I will most likely be working with some aspect of the reflection/refraction data gathered in Costa Rica over the last 2.5 months.  I look forward to seeing many of you again at many future AGU's. 

It has been a while so I thought I would post the text of my AGU abstract.

In July 2007, the U.S. Geological Survey acquired a 60-m-long seismic reflection and refraction profile across the main trace of the Hayward fault in Fremont Central Park, Fremont, California. The profile was designed to determine the geometry, seismic velocities, and possible structural complexities of the fault. The study was along a part of the surface rupture of the 1868 M 7.0 Hayward earthquake. We used single-element, 40-Hz vertical geophones placed at 1-m intervals along the profile with 0.5-m lateral offset from the shot points, also with 1-m intervals. Seismic sources were generated by multiple sledgehammer blows at each shot point. Data were recorded unfiltered in the field on a Geometrics Strataview RX-60 seismograph at a sampling rate of 0.5 ms for 2 s. Geophone locations were measured in 3D using differential GPS. We developed a velocity model using the Hole (1992) code to invert P-wave first arrivals of the refraction data. Seismic P-wave velocities range from about 200 m/s near the surface to approximately 800 m/s at a depth of 13 to 16 m. The velocity model was then applied to the reflection data to develop an unmigrated common depth point (CDP) stack. The reflection data indicate the presence of at least three fault strands in an approximately 20-m-wide zone. We believe the three strands define an upwardly flaring ‘flower structure’, with the central strand being the main strand of the Hayward fault. The three strands project to merge at a depth of about 150 m; the overall dip of the fault zone in the upper 100 m is to the northeast, at about 88 degrees.

I just got settled into my new apartment in Minneapolis and I go back to work tomorrow. This weekend was very busy for me. I flew out of LAX at 11:40 PM on Friday after working 64 hours M-F in 85-100 degrees in Pasadena CA. I arrived in Chicago on Saturday and moved in to my apartment on Sunday in Minneapolis.

The fieldwork in Pasadena was lots of hard work but was fun. We had several logistical and other problems that made us shorten the second seismic line. We were so busy digging over 240 14 inch deep holes in incredibly rocky terrain for our besty seisgun survey that I was unable to take any pictures. One of the advantages of the project was that we compared multiple seismic sources at the same site to see which gets the best data. We tested sledge hammer, accelerated weight drop, and betsy seisgun. It was our opinion that the betsy seisgun propagated the furthest and generated the best data. In the week previous to our field work I assisted in servicing all of our seisguns and learned the inner workings so I would be able to repair them in the field if needed.

I am still currently working on my abstract for AGU and continuing working on my poster. I will keep my blog updated over the course of the school year as things progress.

As my official IRIS internship ended on Friday I thought it would be appropriate to reflect on my goals I set at the start of the summer.

• Conduct actual research to supplement my classroom studies

Acquired data on 9 (7 in 2 months) seismic lines and used PROMAX to make first break picks.

• Gather enough data to produce an AGU poster and then a senior thesis

My poster is about half done and I have a great project to start a senior thesis on.

• Experience the lifestyle of a graduate student

On most weekends I was with Stanford graduate students and have decided that that is what I want to do for the next 3-6 years.

• See the Stanford campus and meet students, faculty, and possible advisor's

I have been to the Stanford campus several times and have met students and faculty.

• See the Bay Area

My parents came out for a 5 day vacation and I saw Alcatraz, Yosemite, Redwoods National Park, and lots of the Bay Area.

• Find graduate schools that conduct active source seismology

Talking with Mike and others I have a list of schools that conduct active source seismology and acquire their own data.

• Decide if I want a Masters or PhD

From what I have observed by talking to people I am know leaning toward getting my PhD.

• Make contacts with people in active source seismology

I have made many friends at the USGS and at Stanford.

• Find out what I want from graduate school

Still really don't know.

• See if this is what I want to do for the rest of my life

I could foresee myself doing this as a career.

Overall I am very pleased with my summer experience and since the USGS is going to continue my internship for an extra two weeks they must be pleased with my work also.

Since my last post I have jumped head first into my project. These past few weeks Mike and I have been going over my abstract and other written parts of my AGU poster. It has been very enlightening to me to exchange ideas off of Mike to see how our ideas are different.

We have also collected all the field data for my project. Just a refresher I am doing a 60 meter long seismic line with 58 valid channels. My project is dealing only with the P-waves while we did collect both P and S waves. My field site is located near Lake Elizabeth in Fremont Central park in Fremont, California.

The seismic line is outlined in red

I have helped preprocess the data by sorting through bad shots and determining which shots should be stacked on top of each other to reduce noise. Stacking the shots was difficult than I anticipated because of the subtle variations in the timing of the initial first break. This proved rather difficult and required lots of guessing and checking because of how high resolution this survey is (1 m spacing).

Below is a stacked image of the data at FFID 1028

After stacking the shots we made some interesting discoveries. We first decided to take a shot and compare how the shot looked at various frequencies. I decided the best frequency was 55-110-220-440 because it was the highest frequency that the reflectors were still obviously present. Then we did our normal 60-Hz notch filter to knock out background noise. This unveiled and interesting scene because our velocity was so low that for parts of the section the airwave arrived before the first breaks. To correct for this I first picked the airwave for every shot and then we applied a high frequency filter at 0-0-80-160 to remove the airwave. After the second filter I was ready to make first break picks. I would first show the picks I made for the airwave so I would not pick at the same location now that the airwave has been filtered out.

The airwave picks are in blue and my first break picks are in red.

After making first break picks we ran several programs to test if I had made any obvious mistakes. After the first round I had 17 shots that needed to be corrected after two more rounds of adjusting picks I had it down to 3 shots. It basically tested if I had any major jumps between picks and if the velocity in one direction was the same as its inverse eg 1-14 had the same velocity as 14-1 of a different shot. After some careful consideration I was pleased enough with my picks to give the go ahead and a colleague created a velocity model based on the inversion code written by John Hole.

My velocity model was plausible but did not give me the obvious low velocity zone I wanted.

Here is the first plot of the unmigrated reflection common depth point (CDP) stack.

Please note that most of the valuable information in this stack is in the first 50m and is obscured in this view.

Many of you already know what is involved in a high resolution seismic survey but for those who do not this is for you.

First, we measure a straight line and place flags in the ground where we will place geophones.

Then we layout the cable placeing a takeout next to each flag.

Then we plugin the geophones into the takeout of the cable.

Then we layout the trigger cable and start the P (Up/Down) wave survey.

Then we hit a metal plate with a sledge hammer to generate our energy source.

Then we begin the S (side to side) wave survey by switching to S wave geophones and using a S wave genertor and sledge hammer.

Then a weight (me) is used to anchor the generator into the ground and then the generator is hit with a sledge hammer to generate theenergy source.

Then we setup a differential GPS base station to determine our exact location.

Then we measure the exact location of every geophone with the GPS.

Then we packup and enjoy the scenery after a 13 hour day.