Tom Wilson, Department of Geology and Geography Environmental and Exploration Geophysics II tom.h.wilson Department of Geology and Geography West Virginia University Morgantown, WV Intro Wave Types and Travel Paths - Example Applications

Tom Wilson, Department of Geology and Geography Environmental and Exploration Geophysics II Course Syllabus Prerequisites Grading Exploration Project Term Report Computer Software/ Computer Labs

Tom Wilson, Department of Geology and Geography Grading 25% on computer labs, 30% problem sets, 10% mid term exam, 20% (Expl project – IB or other)/term report and class presentation, 15% final exam.

Tom Wilson, Department of Geology and Geography For more information on the IB competition see & Exploration Project Option vs. Term Report An exploration project option is centered around the AAPG Imperial Barrel data set used in their annual competition. If you wish to join other students in this competition it is possible to fashion a term report effort around the IB data sets that focuses on prospect development with an emphasis on seismic interpretation. If you wish to do that then you can sign up for the Imperial Barrel Seismic Lab. Lab participation requires that you attend the Barrel meetings and the regional competition in Pittsburgh (late March/early April). The data sets usually arrive early in January. Section and regional competition will be held sometime during the month of March. It all happens pretty fast and will consume a lot of your time.

Tom Wilson, Department of Geology and Geography Imperial Barrel Seismic Resources

Tom Wilson, Department of Geology and Geography Imperial Barrel Component Note that while Geol 554 will accommodate student interests to participate in the competition. IB competition is not a requirement and the class content is not focused on analysis of IB data sets.

Tom Wilson, Department of Geology and Geography Course Objectives I. Provide discussions of basic principles in reflection and refraction seismology and ground penetrating radar. II. Provide experience with the application of these principles to non-invasive investigations of subsurface conditions important to environmental assessment of hazardous waste sites and groundwater exploration, engineering studies, and resource exploration. Student choice of term project and term report help the student focus geophysical applications on their primary interest whether exploration or environmental assessment III. Provide an introduction to computer modeling as a problem solving tool. IV. Develop oral-presentation and report-writing skills.

Tom Wilson, Department of Geology and Geography format of the course, course content, grading … etc? Check your final exam schedule at

Tom Wilson, Department of Geology and Geography How are seismic data sets like those shown below created?

Tom Wilson, Department of Geology and Geography We’ll be covering a lot of the basics. Looking inside the box > Seismic Ears or ground vibration sensors Audible frequency range is about 20 to 10,000 Hz. When you look at a seismic section you are seeing ground vibrations that for conventional seismic data fall in the 10 to 120 Hz range

Tom Wilson, Department of Geology and Geography See Audible frequency range

Tom Wilson, Department of Geology and Geography Translating up and down surface vibrations into electromagnetic signals Class Demo

Tom Wilson, Department of Geology and Geography These signals are sampled at discrete points. They are not continuous or analog recordings

Tom Wilson, Department of Geology and Geography Counting in base 2

Tom Wilson, Department of Geology and Geography Although recording is no longer done on magnetic tape, the tape analogy is a good way to visualize binary idea.

Tom Wilson, Department of Geology and Geography The 8 bit recording range corresponds to a -128 to 127 range of integer values – no decimals!

Tom Wilson, Department of Geology and Geography To see additional detail in the ground motion - to measure the “fractional” motion - you need to increase the dynamic range of the recording system. The engineering seismograph we demonstrated in class today is restricted primarily to the shallower applications since events that have traveled great distances will have very small amplitude (less than 1on the scale of ±128). Dynamic range refers to the number of bits available to store information An 8 bit (1 byte) record allows one to store numbers in the range -128 to 127 A 32 bit record allows one to store numbers in the range -2,147,483,648 to 2,147,483,647. Dynamic Range

Tom Wilson, Department of Geology and Geography Liner and Liner, 1995 Profile data - Processed GPR profile

Tom Wilson, Department of Geology and Geography Miller et al Seismic and GPR methods both record waves that have been reflected from subsurface interfaces. In the one case (GPR) these waves are electromagnetic (and much faster), in the other (Seismic) they are acoustic or mechanical waves (and much slower).

Tom Wilson, Department of Geology and Geography Shot records – Upshur Co., WV Redstone Coal Very shallow high resolution “hammer” data

Tom Wilson, Department of Geology and Geography Different kinds of waves … Body Waves

Tom Wilson, Department of Geology and Geography Surface Waves

Tom Wilson, Department of Geology and Geography Body vs. “Surface” Waves

Tom Wilson, Department of Geology and Geography In general V R <V L <V S <V P But this is not strictly true. The Love wave is a surface wave and its velocity will be equal to the shear wave velocity in the upper medium. The Love wave like the Rayleigh wave is also a dispersive wave. That means that deeper Love wave motion usually propagates more rapidly since velocity increases with depth. Shear waves beneath the surface layers are generally much faster than those in the surface, so in application, the shear waves that we are concerned with generally have higher velocity than the Love waves.

Tom Wilson, Department of Geology and Geography Love waves tend not to be recorded in the conventional seismic survey where the interest is primarily in the recording of P-waves. The geophones used in such surveys respond to vertical ground motion and thus do not respond to the side-to-side vibrations produced by Love waves. Rayleigh waves produce large vertical displacements and are a significant source of “noise” in the conventional P-wave reflection seismic survey. Single component vertical motion detectors

Tom Wilson, Department of Geology and Geography Breaking seismic disturbances down into their component parts Some nomenclature

Tom Wilson, Department of Geology and Geography time and frequency

Tom Wilson, Department of Geology and Geography wavelength and wavenumber

Tom Wilson, Department of Geology and Geography Changing the sinusoid arguments allows us to translate time or distance of travel into a position on the sinusoid Temporal form Spatial form

Tom Wilson, Department of Geology and Geography The seismic wavelet

Tom Wilson, Department of Geology and Geography The wavelet or pulse is a transient disturbance – it comes and goes

Tom Wilson, Department of Geology and Geography Spatial view

Tom Wilson, Department of Geology and Geography A Wave Packet or Wavelet Time domain and frequency domain a different way of viewing the time series See SumofCosines.xls on the class page

Tom Wilson, Department of Geology and Geography The wavelet Any time series can be represented as a sum of sinusoids

Tom Wilson, Department of Geology and Geography How do mechanical waves get from point A to B

Tom Wilson, Department of Geology and Geography You can go straight there or …

Tom Wilson, Department of Geology and Geography The reflection events we see in a seismic section don’t start off looking like this The geologist usually immediately starts to see layers, stratigraphy, depositional history, structure… Fruitland coals- San Juan Basin, NM The migrated stack

Tom Wilson, Department of Geology and Geography Those reflection events start off looking completely different than you are used to seeing in the migrated stack section

Tom Wilson, Department of Geology and Geography When we bang on the ground, the Earth speaks back in a variety of ways This time-distance record shows everything coming in with different shapes, sometimes almost at the same time and sometimes earlier, sometimes later. A real mess!

Tom Wilson, Department of Geology and Geography The seismic diffraction event may seem different that it’s optical cousin But it all boils down to a point

Tom Wilson, Department of Geology and Geography Ground roll = noise to the exploration geophysicist

Tom Wilson, Department of Geology and Geography I should emphasize that this is not just a seismic interpretation course. Seismic interpretation will hopefully be an enjoyable part of the course, but the class will include considerable quantitative effort. The math level required to do work in this class is basic: algebra & trigonometry for the most part. This effort falls under the first objective of the course and that is for you to walk away from this course with an appreciation of the basic physics of seismic, and to much smaller degree, ground penetrating radar. Please look through chapters 2 through 4 and note that geophysics has substantial quantitative underpinnings.

Tom Wilson, Department of Geology and Geography Things to do Skim through chapter 1 Read chapter 2 – pages 7 through 39 Work problems 2.1 and 2.2 and hand in Wednesday