Lec: 8/26 | Course Introduction
Please go over the syllabus/schedule to make sure you have field field trip dates on you calendar. If you have any camping gear needs, let me know. Sharing of equipment (stoves, tents, etc) is good too for keeping the amount of gear reduced we have to transport.
Make sure to sign up for the Overleaf account and related items that I sent to you in recent emails.
Some main points from my babbling today:
geophysics cannot be divorced from an understanding of the site geology and having a geologic model from field reconnaissance and studying previous work.
There are a lot of geophysical methods, some are better than others in different situations.
Many geophysical methods generate data that is necessarily a smoothed or smeared version of the actual geologic structure. This is a statement about the resolution the data can provide. We saw this in our conceptual discussion of the gravity data in the Pine Valley Fault article. Electrical resistivity data also exhibits this characteristic, and we will work with such data a lot.
As we saw, you can still correctly interpret it but it takes judgment. In the article they compared their data curve to pre-calculated "master curves" of gravity data for different densities, fault throw, density contrast, etc. Very tedious, but that's what they had. This would be called forward modeling of the data. Nowadays we can also do inverse modeling, or just inversion, of the data. In either case, interpretation pitfalls exist - so it's up to acquiring geologic judgment.
One geophysical method may be able to detect a geologic contact that another cannot: a simple example to keep in mind.
Measured geophysical values of geologic materials can overlap, even for very different materials. This makes interpretation difficult, and underscores the need to know as much about the geologic environment as possible ahead of time.
We will start to talk about electrical resistivity methods next week. But in the meantime, trying to read the printed chapter I handed out today would be very useful, even if you don't understand some of it.
Lab: 8/27 | Cable Management
Some take home points from our cable management activity:
Electrical cables
Avoid dragging cables
Avoid putting tension on the cables.
Avoid winding up cables over your shoulder or on your arm - this puts tension on the cables as well as "rolls up" winds and kinks in the cables.
The cables can display both short wavelength "kinks" and long wavelength winds. Don't just tug on the kinks, manually unwind them into longer wavelength winds, then carefully rotate them out (like a careful jump roap swing) to the side of the cable that is not being used to coil up from.
Be patient. Roll up the cable clockwise or counter clockwise as needed. Or from the other end.
It's not a race. Be patient. Ask for help. Ideally a group of three people works well.
Etc.
Seismic cables
While these are bit more forgiving than the electrical cables, use the same careful attitude towards them
One difference is that we do coil them up on the circular orange garden hose holders.
Be careful about undoing the winds in the seismic cables, but usually those are easier to deal with than the electrical cable winds.
Etc.
Summary
Field equipment, including cables, are designed to be tough and resilient. But, you never want to the test that they actually are.
The cables, and all the equipment, are expensive! Be deliberate when working with the equipment.
Other Notes:
For our class meeting next Wednesday please start reading the chapter I handed out to you in class on Wednesday, which is also posted here. It's ok if you don't get it all, it's still useful to have looked at some material ahead of time.
Also if you haven't done the Overleaf signup, etc., from my previous emails, please do so