GEO371
Karen Jennings
Review of Zehfuss et al.
The paper submitted by Zehfuss et al. involves the study of alluvial fan
processes and slip rates along the Fish Springs fault of Owens Valley,
California. 10Be and 26Al exposure ages were calculated from boulders
deposited in five alluvial fans along the fault scarp and the relative
offset of the landforms were used to determine recurrence intervals along
the fault, as well as the vertical displacement rate. Soil profiles were
identified in order to aid age correlation of the fans, and to further
investigate fan processes occurring at the site. The results of the study
reinforce previous findings for the ages of fan deposition and the average
rate of vertical displacement along the fault (0.24 + 0.03 m ka-1). The
paper also presents new information on soil development rates in arid
regions.
In general, the paper is straightforward and well-organized. The
significance of the project is clearly stated on page three with the
mention of the 1872 earthquake, and the nearby LA Aqueduct. Zehfuss
describes the methods used in great detail (sometimes too much detail),
and spends a large part of the paper explaining the results and inferences
of the project. I do feel that the paper would benefit from a few more
rounds of editing, however. The paper as a whole is quite long and I
think the text would flow better if condensed. For example, are the long
tables of data really necessary? It seems that there would be a better
way to represent the results without presenting it in one big table.
Also, is it necessary to mention samples that were not used (see note
number 11 in the manuscript below)?
Another thing I noticed was the number of paragraphs that started with a
discussion on how the data might be inaccurate or invalid (examples: p. 16
last paragraph, p.10, p.8 middle paragraph, p. 22 second paragraph, p. 24
last paragraph). Presenting such a statement at the beginning of the
paragraph tends to focus the reader on the negative and guide them towards
thinking the study might be invalid. Considering that you always have
evidence to validate whatever assumptions are being made, I dont think it
is necessary to mention how your data would have been corrupted if the
assumption was not valid. In other words, just state the assumption, and
explain how the data and results show it to be a valid assumption which
will not influence the conclusions of the study. This approach would
also help to cut down on unnecessary text.
Will figure 2a be in color? I had a difficult time identifying the
features in Fig. 2a that were discussed in the text, however, a better
picture would solve that problem. Figure captions are often choppy, and I
think many could be shortened through rewording.
This paper seems to address three different topics; fault displacement
rates, alluvial fan formation, and soil formation. I had a difficult time
understanding what the exact connection was between the three subjects and
how each contributes to the larger picture of what is happening at the
Fish Springs fault. Those three topics should be more thoroughly
integrated before submitting this paper for publication. On the other
hand, you might consider breaking this paper up into two smaller papers;
one focused on the fault movement, and another focused on soil development
and fan processes.
I would recommend this paper for acceptance to the GSA Bulletin with major
revisions. Zehfuss et al. have shown the significance of this study not
only in assessing the vulnerability of the Fish Springs area to
earthquakes, but also in its ability to demonstrate how cosmogenic dating
methods can be correlated with soil profiles to evaluate alluvial fan
formation processes. Before proceeding to publication, the paper should
be condensed and the three focuses of the paper (fault, fan, soil) more
completely integrated. I believe that a couple more rounds of editing
will clear up these concerns.
Manuscript:
1. Expand to eliminate the parentheses. i.e. The cinder cone has been
previously dated with 39Ar/40Ar at 314+36 ka (Martel et al., 1987).
2. Distinct ages of what? of deposition?
3. Maybe you could draw in some little mountains on the figure? That
would help the reader to see how wide the range is.
4. Will figure 2a be in color? It is hard to read the writing in dark
areas of the picture, or to see the bar and ball in light areas of the
picture. Fault symbol doesn't show up in the legend.
Are the faint white lines roads? And what is the squiggly line by the
north fan A (nA)? An active or abandoned channel? (Note: I found out
later that it was an abandoned channel , but not until near the end of the
paper).
5. It took me a while to orient myself and figure out what I was looking
at in Figures 3a and 3b. Maybe dashed lines would help?
6. Is there a better way to represent the data rather than the use of
long, dense tables?
7. What will the rates of soil development say about fault movement
exactly? Spell it out!
8. Is it necessary to include this (the funding history)?
9. At this point in the paper, I was still unsure about how the soil
profiles would contribute to the tectonic history.
10. This paragraph was hard to follow. I'm not sure how to remedy that
except to suggest another figure showing how faulting cuts across an old
fan surface, and then new deposition rolls in and covers it.
11. I don't know that it is necessary to mention this sample if you didn't
use it. I would suggest either putting this statement in the table
caption, or eliminating it completely.
12. Choppy sentence structure. Is this information necessary to include,
anyway?
13. What is the purpose of this procedure? To isolate the Al and Be?
14. Production rates of what? Nuclides?
15. What kind of sedimentological characteristics?
16. What was the purpose of comparing the soil development in Owens Valley
to elsewhere? How does that contribute to the study?
17. This last sentence could use further explanation.
18. What's the source for the north fans? Are they derived from Birch
Creek as well?
19. I can't find the channel levees or the notch on figure 2a, but that
could be because I have a xerox to look at.
20. I'm confused - on page 15 you say that "We are unable to distinguish
how much of the 4.3m of scarp height is a result of fault slip post-dating
the deposition of north fan B." But here on page 16, you say that there
has been "1 m of offset since the deposition of north fan B." That seems
contradictory.
21. Is it necessary to mention this boulder since it was not included in
the average?
22. I don't understand what this contrast has to do with your study of
fault movement on the Fish Springs fault.
23. Which model fits your data and observations better and why?
13 April 1999
Review of "Slip rates on the Fish Springs fault...."
By dating fan surfaces Zehfuss et al. present a long, detailed chronology of faulting rates along the Fish Springs fault. Their cosmogenic isotope data improve and support existing estimates of fan surface ages and displacement rates. The Be and Al age estimates support the relation of fan deposition to glacial episodes. Soil development rates on the debris fans are also presented, suggesting relatively slow rates of soil formation for fan surfaces at Fish Springs or modification of the soil by surface processes.
This paper is very well written in terms of grammar and sentence structure. The paper is loaded with data and descriptive figures. The logic behind the interpretations is presented better in some spots than others. This paper is very near being ready for publication. However, if feel the paper could be strengthened by 1) providing a stronger explanation of what the main purpose of introducing the soil development data is (augmenting cosmogenic data by supporting age estimates?, introducing soil development rates on fans in Fish Springs?, providing insight into fan deposition?, all three?), and 2) shortening or major revision of the West Fan portion of the paper. For me, it seems like there are two data sets: isotope dates and soil development data. You present both data sets and interpret both well, but I was left wondering exactly why both are presented in the same paper, the link between the two is still sketchy for me. The title only mentions Be and Al age analysis, but half the ms is soil development analysis. Throughout the paper (see sections marked with *) I was led (or hinted) to believe that the soil development data help to augment the isotope dates, but I was left at the end of the paper only believing that the soil development data could be used to determine that development rates are slower at Fish Springs than elsewhere (and that the cosmogenic data augmented soil development interpretation, not the opposite). I was also confused by the rather lengthy explanation of the West Fan (p. 23-25), which I feel left me wondering what exactly you were trying to get across to the reader. It seems that there are some major discrepancies encountered at the West Fan, and the two models you present do a good job of offering possible explanations of those discrepancies. However, I would have rather seen a clearer/shorter section detailing what YOU think the answer to most probable explanation (or 'Model') for the West Fan is. I was left wondering that no model could ever work.
SPECIFIC SUGGESTIONS:
1) Is this paragraph really necessary? Can you cite someone else's techniques?
2) How about adding a little explanation of how comsogenic isotopes work? Is everyone reading this going to know what is going on with cosmogenics? Some readers (like me) could probably use the explanation.
3) Again, a cosmogenic overview would help here.
4) I think this is the first mention of a 'model'... and the glacial epochs have not been mentioned for a while (the intro?). This sentence makes sense after finishing the paper, but when reading it for the first time I was a little confused. (see suggestion 5, below)
5) Page 23 is the first (or second) mention of glacial epochs. It is not clear until p. 29 Implications, how glaciers fit into the picture. Can you add a little more to the Intro so that glaciers will fit into the picture sooner.
6) Figure 1 just looks like a bunch of words on a page to me. The DEM will probably help here.
7) Figures 3a and 3b were the least effective for me. Adding labels (on the picture) will improve them.
8) Figure 4b... vertical spelled wrong.
Review of "Slip rates on the Fish Springs fault, Owens Valley, California:
10Be and 26Al exposure age analysis" by Zehfuss and others.
Zehfuss et al. use a combination of cosmogenic isotope analysis and soil
development along at the Fish Springs fault. Cosmogenic isotope analysis
was used on samples taken from large boulders at the surface of different
mappable alluvial fan units. The cosmogenic isotope ages provide limiting
ages for fan emplacement. Zehfuss et al. used the PDI method for
relatively dating soil development. Both methods correlated fairly
accurately in the relative sense. Previous research by Martel provided
the age of the Fish Springs cinder cone. Using Martel's work and their
cosmogenic isotope ages of offset fan units, they determined slip rates
along the Fish Springs fault (0.240.03 m ka-1). Zehfuss et al. also nobly
try to determine recurrence intervals for the fault (3200 to 6500 yrs).
This paper is extremely well written. There are only few minor marks on
the manuscript regarding grammar. There are also a few locations in the
manuscript in which vague or confusing sentences could be improved upon.
Illustrations compliment the text well. Conclusions are scientifically
sound.
This paper should definitely be accepted for publication with only minor
revisions. Besides clarifying a few vague sentences the only item that I
strongly believe should be included is pre-debris flow inheritance of
cosmogenic isotopes. This could be done in one paragraph or even in a
couple of sentences. Also, a statement of what remote sensing was used
for would be helpful. This could be one sentence saying what they did and
how it supports you field work. Lastl,y I feel as though you should
re-title the paper. The paper is more on the dating (definite and
relative) of the fan deposits, modeling fan emplacement, and determining
fault offsets. Slip rates get half a page all the way back on page 26,
this is less air time than the recurrence intervals and that is not in the
title.
I do not have specific comments on the manuscript, rather I have thoughts.
Here is my rambling on pre-debris flow inheritance:
I feel the authors do not regard pre-debris flow inheritance of cosmogenic
isotopes as a problem. This would mean that all boulders had to come from
greater than 2 m in depth to be isotope free at the time of emplacement.
This seems highly unlikely and it seems as though some boulders would have
to come from the surface at the initiation of debris flows. If source
areas are large you may have many surface boulders from the source area.
Another possibility is storage in the valleys could pump up the
inheritance. In anycase I don't think you are getting isotope free
boulders. If you feel as though you are, tell the reader why you think so
(small source areas, no storage in valleys, or as Paul later told me about
the glacial moraine debris flows which I could buy, etc.). Inheritance
could also account for some of the noise in the ages, even though you are
pretty internally consistent.
It would also be more clear if the you stated that no samples need
geometric corrections. I think I remember reading that most samples were
taken from flat surfaces. But what about the other samples?
There is one sentence stating that you also used remote sensing. Well
what did you use it for? lithologies, weathering? This is an interesting
check or support for you field work. Tell us what you looked for and why
you did it. Or even leave it out all together.
You mention erosion of the fan surface. For this to mess with your
cosmogenic ages it would have to erode up to a meter or more (you could
determine the exact erosion depth which would start to significantly
change your boulder ages). What range of erosion depths do you think are
possible for this area? Would this change the boulder population? Do the
old fans have more boulders at the surface?
You talk about cosmogenic isotope measurement uncertainties. What can you
assign as absolute uncertainties for cosmogenic analysis as a whole (alt,
long, magnetic field and production rate)20%, 30% or even 50%? I don't
know if this is important at all.
Finally are there really fish in the springs around there?
Kyle Nichols
003 Perkins Hall
Department of Geology
University of Vermont
Burlington, VT 05405
802-656-3398
Review of Zehfuss, et al.
April 13, 1999
"Slip rates on the Fish Springs fault, Owens Valley, California: 10Be and
26Al exposure age analysis," by Zehfuss et al., involves determining the
ages of some alluvial fans using cosmogenic isotopes and soil development.
>From these ages, and from measurements of a fault scarp that crosses the
fans, they have calculated long-term slip rates on the Fish Springs fault.
I am still undecided on whether this paper will be accepted in its
current format by GSA Bulletin. I realize they allow huge papers, and
that is where people publish if they want to be able to include every last
little detail of their research, but this paper seems awfully long and has
so many very different concepts worked into it that it is difficult to get
through. One idea would be to break it into two papers, one dealing with
the cosmogenic dates for fan surfaces and the displacement rate on the
fault, the second paper would be shorter and discuss the soil development,
as calibrated by the cosmogenic isotope ages.
Another problem I had was that I felt pummeled with an abundance
of data and observations. In some places it reads more like a thesis than
a journal article (especially in the sections where they describe every
fan unit with loving detail). It seemed that some sections could be
shortened into tables (a table of fan unit descriptions, of scarp
characteristics, of cosmogenic ages on each fan, soil descriptions).
Again, I realize that GSAB lets people write long papers, but I think
shortening some sections into tables would make the information more
accessible, and easier to compare between fan surfaces. I also never
really understood how exactly you turn fan ages and scarp heights into
displacement rates. It could entirely be that I missed it, but I still do
not understand how that all works.
With that all aside, this paper is for the most part well-written,
includes a lot of information, and will be useful for people trying to
determine faulting rates from displaced fan surfaces, and those who need a
calibration of PDI with numerical (rather than relative) age estimates.
It will be a valuable addition to the fan, cosmo, and soil literaturebut
it would help if it were in a more user-friendly format.
That's what I said before class. Now, after class, I have a few more
comments:
Figure out what the central theme is, and build all your evidence around
that theme (I got messed up on the soils stuff because I thought you were
using it to figure out _ages_ and support your cosmo data. I know now
that it was to figure out how the fans were deposited and what the
relationship between deposition and faulting may be). Don't worry about
splitting it into two papers, if you can integrate the soils work better.
I don't have numbered comments--but I've marked up the text considerably.
Review of Zehfuss, et al:
"Slip rates on the Fish Springs fault"
4/13/1999
The authors present evidence from three data sets (cosmogenic
isotope data, soil data, and topographic data) to determine time-averaged
slip rates on the Fish Springs fault in southern California. They use the
age constraints provided by cosmogenic isotope analysis, mostly in
conjunction with the topographic data of alluvial fans offset by faulting,
to infer the average slip rate of the fault. Their data from analysis of
several soil profiles on the fans in conjunction with the age constraints
imposed by cosmogenic nuclides allow the determination of rates of soil
formation on the fan surfaces.
This paper is well-written, with few grammatical or typographical
errors. By my reckoning, the science is robustand rather impressive, given
the amount of work done in the amount of time used. However, I believe
that the paper itself would be strengthened considerably by three major
kinds of revisions:
1. Edit and condense the paper considerably in certain sections. Many of
these problem areas provide too much detail, and create the feel of a
thesis document rather than an article in an academic journal. These
sections are noted on the manuscript with marks for deletion or revision.
2. Clearly separate observations/results from your own interpretations in
your "Results and Interpretations" section. I found it difficult to
extract the facts from the inferences in some of these sections; putting
each under separate headings would clarify your argument considerably. In
most parts of the paper, these sections are more clearly separate.
3. Focus on what you do know and on those things that you can make
reasonable speculations about, and spend less time explaining the
difficulty of arriving at those conclusions. As your paper stands, you
shoot yourself in the foot by going into such detail regarding
uncertainties. After I read that section of the paper, I found myself
wondering: a) why do this study at all if the uncertainties are so huge,
b) why report your results in a journal if you cant really say anything
conclusive, and c) can I believe that any of the rest of your work has
credibility. However, I know that these questions are too extreme and your
uncertainties arent really that huge, but my immediate gut reaction was to
dismiss your work and it would be a shame if other people reacted
similarly once your article is published. I appreciate the effort you put
into wrangling mentally with these difficult processes, but Id rather not
read about the nitty gritty of it in your paper. If nothing else, just
bracket the values youre trying to determine so precisely, and leave it at
that.
Additionally, reconsidering the need for such extensive modeling of the
fan processes might also improve the paper. This consideration needs more
exploration, and depends largely on the ultimate goals of the paper. These
goals are too broadthe many threads that are woven into this article
distract from the significance of each individual strand. I would suggest
more narrowly defining your goals, and letting some of the pieces become
supporting evidence, rather than projects unto themselves.
Review of Zehfuss et al., Slip rates on the Fish Springs fault.
Overall, this is a greatly improved manuscript since my last reading. It is very well-written, superbly illustrated, and rich in data except...for several pages at the end. Excepting these pages, it is better than most GSAB manuscripts to which I am subject as associate editor.
The manuscript is long, even by GSAB standards, so I have tried to indicate places where it might be shortened by removing sentences or paragraphs that seemed less germane -- my biggest target is as you may guess..the pages near the end.
There are sparse minor edits on the ms. Otherwise the ms is quite clean and by all means ready to get out the door, except of course....you know! You will need a cover letter and list of suggested reviewers. Alan can certainly help with such a list. Steve Reneau at Los Alamos come to mind as a good crossover person who knows both isotopes and soils. Merith?. Milan Pavich?
The entire section rambles and after three readings I still cant figure out exactly what you want to get across to the reader. You need to distill this section into a set of meaningful paragraphs that are logical and lead the reader through a cogent argument. As it stands, this section will alienate most readers and severely risk rejection in review. It is nowhere near the quality of the rest of the paper.
I would start the section with a statement of data and if needed, a statement of what you feel the contradictions are or the problem is. Be blunt. Then, on the basis of those contradictions and data develop one or two models to explain what you see. . As a reader, I have no idea why you are going through this "song and dance" because you have not pointed out exactly what the problem is, just that it is insoluble. Remove all the waffle words and uncertainty and self-pity that now permeates this section and simply and straightforwardly tell the reader what your best educated guess is as to something you will never know...how the west fan really works! I favor one integrated model is we can create it.
Model paragraphs A and B are better than the intro but I still wonder...can you come up with one, short cogent explanation?
I would cut out everything you have written and start simple. See if you can get away with just a few succinct paragraphs that point out the problem and then attempt to solve it.
Overall, my feeling is that you have two very strong data sets. You need to interpret them but don't dilute the data by getting so far off into geo model fantasy that reality gets left behind. Keep tying your hypotheses to data!