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.