Sunday, September 18, 2011
It was my third time, if I am counting right, went through the Seismic Data Acquisition. As many sources mentioned, there are actually 2 kinds of Seismic Methods regarding to the imaging and profiling subsurface.
Reflection seismology (or seismic reflection) is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth‘s subsurface from reflected seismic waves. The method requires a controlled seismic sourceof energy, such as dynamite/Tovex, a specialized air gun or a seismic vibrator, commonly known by the trademark name Vibroseis. Reflection seismology is similar to sonar and echolocation.
Seismic refraction is a geophysical principle (see refraction) governed by Snell’s Law. Used in the fields of engineering geology, geotechnical engineering and exploration geophysics, seismic refraction traverses (seismic lines) are performed using a seismograph(s) and/or geophone(s), in an array and an energy source. The seismic refraction method utilizes the refraction of seismic waves on geologic layers and rock/soil units in order to characterize the subsurface geologic conditions and geologic structure.
The definition from the Wikipedia above will make you understand clearer, hopefully. This time, the seismic type we have done is the Reflection Seismic one.
We gathered in Museum Geologi (Geological Museum) in Jalan Diponegoro, Bandung at 12.00 PM. There are Wadya and Aulia, as the lecturer’s assistant (final-year student of Geophysical Engineering ITB), Mr. Wiyono and Ms. Bernadette (Ph.D student from Stuttgart University, Germany), also Mahardika, Manda, Dyna, Ellena, Meisa, Nurul, Ricki, and me (the 4th-year student of Geophysical Engineering ITB) who are coming to participate in the data acquisition. Mr. Wiyono was also one of the first batch-former member of TERRA ITB (Geophysical Engineering ITB Student Organization). Using two cars, we departed at 12.15 PM, directly to the location decided. Through Jalan Dago, Jalan Dago Giri, Pagerwangi area, we arrived at Gunung Batu area at about 13.15 PM. It was one hour far from the museum.
The scenery I looked along the travel from the museum to the location was incredibly amazing. Not that amazing, where the natural phenomena or anything else, but, it is amazing in the way you stare at them one by one. It surrounds you in daily, but, there were no moment for us to take a look at the beautiful scenery, and admire them in deep. So, this was amazing.
Started with the arrangement of all the equipment. Locating the 40s five-meter-interval-geophones along the line, connecting the geophones to the analog-to-digital-converter to the power source to the frequency generator, and so on, is the always very first step after we arrived at the acquisition site. It took energy more than we thought before, but it was fun, after all. I don’t remember how many geophones were in this project exactly.
So, those equipment with many other tools together operated to get the frequency of the wave travelling through the layer of the subsurface. Each layer, each components of the layer will have their own characteristic for every seismic wave travel pass through it. So, the character will describe a different imaging or interpretation regarding to the structure of the subsurface. The vibroseis generated every 10 meter (4 vibrating times each point). In the short time, we will have many data, more than the conventional way.
At 16.00 PM, we already got all of the data needed, and the project for today is done. Thank god for the calm weather. It helps us a lot.
And finally, here they are, the team for today: