Benjamin Brophy

June 12th, 2015

This past weekend I took a trip to Salt Lake City to collect seismic data. I had never been to Salt Lake City so when we arrived Thursday afternoon I enjoyed grabbing a sopa from a roadside taco stand and seeing their awesome library, which had its own beehive and an awesome rooftop view!

This summer I am working with Lee Liberty of CGISS at Boise State University. The purpose of surveying Salt Lake City is to image the subsurface and identify the location and extent of the Wasatch Fault which passes right through downtown Salt Lake City. Identifying this fault will be able to help update building codes and assess earthquake hazards in Salt Lake. The fault produces provides a large earthquake about every 300 years and it is overdue!

To complete our survey we needed a van, a trailer with a 500 lb hammer, and a long streamer of geophones. Geophones are incredibly sensitive seismic instruments which apparently turn seismologists into psychics - I have been fascinated the last few weeks seeing people staring at geophone readings on a computer saying "Oh, a car just drove by." or "There must be a train going by about a mile from here." or "Stop walking by the geophones!" or "Look, this reading is from an earthquake in Japan." or "Somebody just did a triple somersault and then a cannonball into a pool in the Mediterranean Sea.". Our streamer is a 60 meter firehose which contains horizontal and vertical geophones every 1.25 m, as well as a lot of (heavy) cables to transmit the geophone reading back to our headquarters - the van. The van drives 2 meters at a time, dragging the trailer and firehose, and then stops to drop the hammer. A mechanism on the trailer pulls the hammer vertical against a thick rubber band until it releases and clangs into the ground with an enormous amount of noise - which is amplified by a steel plate placed underneath to protect the street. The geophones record the echos of the waves produced as they reflect and refract in the Earth's crust. 

Here's a closer look at the geophones - the red one detects vertical motion while the orange one detects horzontal motion.

To get long straight profiles on relatively homogenous terrain, we drove up and down the streets of SLC making out hammer shots.

I had a few different jobs. One was the hammer operator. It seemed simple but took a bit to get into the rhythm of lifting and drop the hammer quickly enough that we can keep moving, but with a few seconds of space to the sensors reset once the van breaks. When operating the hammer I just had to help the van driver make sure they stopped at 2 meters ahead of the last shot. I got to wear earmuffs for this job because, once again, the shots are loud! The job I spent the most time on was manning the streamer - since the streets aren't quite level, it was necessary to lug the firehose back to the center of the street every few shots. And the sweet life is driving the tail vehicle - this job is the drive another truck behind the end of the firehose, listen to the radio, and eat whatever snacks I happened to bring with me... you know, for safety.

We started preparations at 4:00 am on Friday morning in what we believed would be a downtown, non-residential area... but when we started shooting at around 5:20 am it became clear that there were quite a few inhabitants on our first street. Most people came out just to check out what was going on, but a few residents were pretty furious that they had to experience 10 minutes of loud noise passing by their apartment. Some residents insisted there were no earthquakes in Utah! I felt like we were the mad scientists or skeptics in a disaster movie... Trust us! This is for your own good! We are protecting the city from catastrophe!

Friday, we toured many short residential streets in North SLC. I discovered that banging the noise of a hammer on asphalt is nothing compared to the cacophany produced from a shot on concrete. We went up a narrow concrete alley in which the hammer echo was deafening - but it was worth it when we got to the end I got the following awesome snapshot of us driving up to the Capitol. To celebrate a hard day of work, we went out for Ethiopian food, which was a brand new experience for me! We ordered a nice platter for four of spongy bread covered with all sorts of delicious concoctions of lentils and beans which I enjoyed eating with my bare hands.



On Saturday, we went about 5 km straight across 200 South escorted by police officers to help us through traffic lights. We started at 8:00 am due to the previous day's complaints. With the police around we had many curious people but no gripes! We ended the day approaching University of Utah, which you can see below. Sunday, we did about 5 km again down 700 South, ending at the cemetery at the end of the street. To be respectful, we did not clamor through the cemetery with all of our equipment. ...Until Monday morning. Then we wrapped up about 9:30 am on Monday and headed back to Boise!

May 28th, 2015

Hello! I am enjoying my week at New Mexico Institute of Mining and Technology in Socorro! I am enjoying a crash course in geophysics, and enjoying my first forray into the desert. I saw a tumbleweed and a roadrunner for the first time! Saturday I will head to Boise State University to start my internship. This message will self-destruct in 12 seconds.