GEOL 492/692 - Applied Geophysics
Preparation for Field Exercise
Contents
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Additional Resources
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Objective and Setting
This spring break we investigate the shallow geophysical characteristics of the high-standing parts of the
muddy and sandy V-Line
canal bank within 2.5 miles west of the power plant at the Twenty Six Foot Drop,
west of Fallon
and of the rocky Truckee Canal bank within 1 mile north and south of the Bango Rd. bridge across the canal.
Please make sure the instructors (Louie or Huebner) have a copy of the the
Geology department's emergency contact form
that you have filled out recently. Amr Wakwak has copies and is distributing them.
Each participant must also read the permit application
document, which explains what we have promised to do and not do. If anyone violates any
of our promises, such as driving at more than 5 mph on the canal bank, we risk getting
ejected from our field area.
Since we are close to home, on each of field day will leave at 7:00 AM from
the top deck of the Whalen Parking Garage, and return there each night, probably about 7:00 PM.
I will have parking permits so students driving to the Whalen Garage Monday through Thursday
will be able to park there all day.
Students may bring their own vehicles to the field area, but they must still meet us at 7:00 AM
at the Whalen Garage, or 7:30 AM at Pioneer Way (west end) and US 50 west of Fallon,
and they must do so entirely at their own risk.
Each student will not need to bring any camping or cooking equipment for
our local work, only daily food and drink. You may also need any medications, toilet paper, etc.,
since we will only go into town at lunch time for a restroom break.
Many of the items on the personal equipment
list are still necessary. Be prepared especially for wildly variable weather
conditions.
We may delay our work during fierce storms, but we will have
to make up storm days (or for equipment failure) on Friday and Saturday.
If in doubt about the weather, come that
day to the Whalen Garage at 7:00 AM anyway, and Louie will be there to let you go
home if the weather is too awful. Or call Louie's cell phone at 6:00 AM.
Assignment
Each team of two or three students will take primary responsibility for one of the
5 types of measurements we will take in the field:
- Seismic Refraction and ReMi: Mahesh, Kristin, Sean
- Seismic Reflection: Bryce, Mayo, Danny
- Gravity and Theodolite: Betsy, Annie, Sue
- Magnetics: Wendy, Dan
- Resistivity and EM: George, Scott
Each team is responsible for developing a detailed plan for
how we will prepare the instruments, conduct the field experiment, and
analyze the results. We will coordinate the surveys so everyone gets
experience with each of the methods.
The seismic teams can work with Louie to prepare, and the other teams
can work with Huebner.
Guidelines for proposing the survey plans are below.
Finished plans should include complete and detailed checklists
of every item that will go to the field, data sheets and/or software disks,
instrument operation instructions, maps showing proposed survey locations, and
schedules for work by each team.
Designing a Survey Plan
Each team should develop a detailed plan in writing to guide us
in mobilizing, performing the fieldwork, and sharing and analyzing the
results. In essence, a complete plan would answer all of the questions
below. Starred questions need to be answered by Mar. 7. More questions,
related to each type of survey, are found in the sections below for the various
surveys. Please work with me, other Department faculty, and the other teams
to answer the questions, one by one. You aren't expected to be able to answer
them all by yourself. The written survey plan will naturally help you write
your field report.
Mobilization (all methods)
- **What instruments are needed for the survey?
- **What instruments are available to us?
- **Who oversees the instruments? Are they available?
- **Are the instruments in good order? Have they been recently tested in the lab
and on the ground? Need they be calibrated?
- **What supplies are needed to operate the instrument and record data? Batteries?
Special paper? How are batteries to be charged, or sensitive materials stored?
- **If the instruments need repair or supplies need to be obtained, can this be
done before departure?
- What provision can be made for instrument failure in the field? Would any
tools be useful? Spare parts?
- **How and when are the other participants to be trained in the use of the
instruments?
What manuals are available? Can brief instructions for field use be written?
Data entry forms prepared?
- **What items and procedures need to be put on a checklist that can be completed
during mobilization?
- **How can the instruments be shipped to the field area? Are they especially
sensitive? Do special arrangements need to be made to borrow them from
the Bureau of Mines, DRI, or other Universities?
- **Are there materials or supplies that can or must be obtained at the field
area?
Where and when will this be done?
Fieldwork (all methods)
- What location and elevation accuracy is needed for survey stations? Do they need to be
surveyed in? Could pace-and-compass locations be adequate?
- What site or geologic factors will contribute to successful bedrock profiling
with this technique? Where could these be present in the field area?
- What site or geologic factors will contribute to successful shallow profiling
with this technique? Where could these be present in the field area?
- In what parts of the field area would this technique help to constrain the
interpretations from another technique?
- In what parts of the field area would the use of this technique be difficult?
Are there access or surveying problems?
- How will the instruments be moved to different sites in the field area?
When will vehicles be required? Will some stations have to be reached on foot?
- How many people and how much time are needed for each station, or each
experiment?
- How much area or how many kilometers of profile can we do while we are in the
field?
- How can a schedule be set up so everyone uses each of the instruments in the
field?
- Where will the survey stations be? What profiles or areas will they cover?
In what order will they be measured?
- How will the data be labeled and stored when it is collected
to avoid loss or confusion later?
- What data quality-control procedures can be used? Can data be immediately
reduced or plotted in the field to check for accuracy?
- Can initial results
be used to guide the other techniques? Or to adjust survey plans on the fly?
Interpretation (all methods)
- What procedures will be used to reduce and interpret the data? Would any
results of the other surveys be needed? Would this survey's results be
useful to another's?
- How and when will the data be disseminated to the other students? How will
needed accessory information, such as station locations and instrument
settings, be provided?
- Are there any items or concerns that need to be added to this list?
References
Telford et al., our textbook.
Compton, 1962, Manual of Field Geology, chapters 2, 3, 4, 11.
Dobrin and Savit, 1988, Introduction to Geophysical Prospecting, pages 3-8 and as noted below:
SURVEYING
Instrument overseers and information source: John Bell, Geoff Blewitt,
Nevada Bureau of Mines and Geology
- **What instrument would be easiest to use while providing enough accuracy?
Handheld GPS? Geodetic GPS? Kinematic or stationary? Absolute or differential?
Alidade and plane table? Laser transit?
- **What maps, airphotos, and remote-sensing images are available? In what forms
will copies be needed before, during, and after field work?
- What horizontal and vertical control has already been established in the
field area? Are control points accessible? How will they be tied in?
Ref: Compton, chapters 6, 7, 8.
GRAVITY
Instrument overseers and information source: R. Karlin, G. Oppliger
- **What special precautions need to be taken to assure the stability of the
gravimeter? Are extra batteries needed?
- Are any absolute gravity control stations available near the field area?
When should they be measured?
- What gravity measurements have been made previously in the field area?
How will our survey improve upon that work?
- Where should control stations be established, and how often should they be
measured?
- Are any data reduction or modeling packages available? Can they work
in the field?
- What sources of local rock density measurements are available?
- What accuracy is needed to make a useful interpretation of basement topography?
What procedures will enhance accuracy?
Ref: Dobrin, pages 498-503, 505-506, 528-535, 547-553, 561-586, 602-604,
613-621.
RESISTIVITY SOUNDING
Instrument overseer and information source: R. Petersen; also G. Oppliger, and
Ken Taylor at DRI; .
- **Are the instruments working and ready for the field? What can be rented or
borrowed?
- **What power sources are required?
- What is the maximum electrode spread, loop area, or time gate?
What is needed to sound to our target depths?
- What are the expected depths of penetration for each of the available
instruments?
- Are special procedures needed to properly ground electrodes in materials
such as dry gravels? Measure dipole lengths? To lay out loops of known area?
What tools and supplies will be needed?
- What will be the effect of the water table?
- What interpretation or analysis packages are available? Can analysis be
done in the field? How will data be recorded, or downloaded?
Ref: Dobrin, pages 750-768, 815-831, 833-842.
MAGNETIC
Instrument overseer and information source: G. Oppliger
- **What instruments are available and working?
- **Are recording base stations available? Gradient instruments?
- What magnetic surveys have previously been performed in the field area?
How will our survey improve on them?
- Where should drift control stations be located, and how often should they be
measured?
- What accuracy is needed to detect the target basement topography? What if
the bedrock changes from volcanic to metasedimentary?
- What will be the effect of volcanic materials within the sediments?
- What interpretation or analysis packages are available? Can analysis be
done in the field? How will data be downloaded?
Ref: Dobrin, pages 633-678, 685-710, 723-733.
SEISMIC
Instrument overseers and information source: J. Louie
- **What recorders, cables, and geophones are available? Need any be rented or
borrowed?
- What seismic surveys have been performed in the region? What were their
results?
- What seismic velocity measurements are available for our area? If none,
what are the likely velocities, and their contrasts at the basement interface?
- What line lengths are needed to locate basement refractions for different
target depths? What are the possible dips?
- Which geophones should be used? Can an S-wave experiment be conducted?
- Will hammer blows provide enough seismic energy? Should another source be
considered? At which sites will hammer surveys have the most chance of
succeeding?
- **How will proper operation of the roll-along switch be assured?
- What arrivals will likely be observed? How will they be interpreted?
- What 3-d or pseudo-3-d shallow surveys are possible with the available
time and equipment?
- What fan shots (off-line) will be possible and helpful in interpretation?
- What areas are most conducive to getting good high-resolution data?
What condition of the water table is helpful?
- **Where are the buried colluvial wedges of possible earthquakes most accessible to
reflection surveying?
- **Where are fault offets of buried neogene channels most accessible to
reflection surveying?
- How small a hammer source can be used? What tests will need to be done
in the field on different sources?
- What interpretation or analysis packages are available? Can analysis be
done in the field? How will data be downloaded?
Ref: Dobrin, pages 58-68, 78-90, 450-459, 473-482.