Julius - lookup:

Baer, G., Schattner, U., Wachs, D., Sandwell, D., Wdowinski, S. and Frydman, S., 2002. The lowest place on Earth is subsiding—An InSAR (interferometric synthetic aperture radar) perspective. Geological Society of America Bulletin, 114(1), pp.12-23.

Amotz

Please check the following link and PDF attachments.

https://www.researchgate.net/publication/235346918_Late_Quaternary_faulting_and_subsidence_in_the_central_Dead_Sea_basin

Article Late Quaternary faulting and subsidence in the central Dead Sea basin

Thanks @Amotz, I was reading exactly that paper and comparing with Nof, 2012. Nof place the locus of uplift directly at the Dead Sea (and asoc. to isostatic rebound). But to me there is problem in the Nof paper, the pattern of uplift from INSAR may also fit a classical elastic model of normal faulting.

Thanks @Arvind, I have seen these papers before, however none of these papers discuss this apparent paradox between vertical deformation at different time-scales.

Seems that the history of the Dead Sea involve complex patterns of vertical deformation through time.

Dear Julius,

The long time-scale subsidence is well documented and apparent. Pronounced faults and elevation differences are limited to the rift area. The mentioned InSAR studies cover a fraction of the geological record and are limited to ~10 years of observations. The subsidence documented by InSAR is limited to the edges of the Dead Sea and is related to dissolution of a salt layer underlying the lake's shores. It is limited to a few km of the shore. The observed uplift is of much longer wavelength of tens of km and is best explained by the upper crust response to the water level drop (elastic rebound). These are not contradicting phenomenas, rather two sides of the same coin, and a result of the ongoing water level drop of the Dead Sea. One is local and the other is of regional scale.  

Hello Ran, thanks for your reply

I must say that I' am a novice in the Dead Sea, I started studying some publications since a few months after a fieldtrip to Jordan. There are a lot of papers but yours captivates my interest. I'm attempting to unify observations of vertical deformation at different time-scales.

Thanks for the clarification about InSAR deformation. I agree with you, subsidence is limited to the rift area (refs) in most cases, and the pattern of decadal uplift by InSAR is at much larger regional scale. As I pointed out in the question, the interpretations seems to be the paradox, not the observations. Tell me if I'm wrong, but I understand that the InSAR used in your study lack of estimates just on the Dead Sea, the area that suppose to be subsiding at longer time-scales. According to your paper, to replicate the deformation pattern from InSAR the maximum uplift from elastic model should be directly at the Dead Sea, which is logic if isostatic rebound is involved; but if we see the structure this is the hanging-wall block subsiding at long-term also Bartov 2006 estimates 1m/ka subsidence at the center of the basin at millennial scales. Sorry for attaching your figure but help to clarify, the  model is similar to a bell and has its maximum is just at the Dead Sea, dashed line and arrows.


If the model is correct, then how to conceal these observations? You  mentioned the similarity between topography and InSAR pattern beyond the edges of the Dead Sea. (See figure attached). Are these vertical isostatic displacement purely elastic? or a part of this deformation stay in the crust as permanent uplift counteracting subsidence at longer time-scales?.

Thanks again Ran for your reply, and your opinion would be very appreciated

Julius

Dear Julius,

"Tell me if I'm wrong, but I understand that the InSAR used in your study lack of estimates just on the Dead Sea, the area that suppose to be subsiding at longer time-scales."

You are correct. The InSAR observations are limited to areas that are not covered by water or does not undergo rapid changes like the mud flats around the lake.

I would suggest you to read a very good summary of the Dead Sea history and observations/interpretations:

Shamir G., 2006, The active structure of the Dead Sea depression, Geological Society of America Special Papersm v 401, p. 15-32.

According to your paper, to replicate the deformation pattern from InSAR the maximum uplift from elastic model should be directly at the Dead Sea, which is logic if isostatic rebound is involved;

We assume the uplift is a result of an elastic rebound due to the dead sea water level drop. If you use the most simple model, you can use the center of mass of the dead sea water body as the removed load. This center is marked as X in Fig. 8 in the paper

but if we see the structure this is the hanging-wall block subsiding at long-term also Bartov 2006 estimates 1m/ka subsidence at the center of the basin at millennial scales.

I agree. The subsidence is estimated (Bartov, 2006) as 1 mm/y and as you said limited to the internal area of the basin. I'm not aware of any attempt to model this subsidence and I assume it will not have a very large-scale effect away of the transform area. That will depend on the mechanism that cause the subsidence of course, but in any case, I assume it would be different than the pattern modeled by elastic rebound as we demonstrate in the paper.

Sorry for attaching your figure but help to clarify, the  model is similar to a bell and has its maximum is just at the Dead Sea, dashed line and arrows.

Attaching the figure is fine, of course. Keep in mined the model only takes into account the effect of elastic response. Ant other deformation mechanism will have to be taken into account and will change the shape of the model accordingly. Depending on the mechanism, this change an be dramatic or minute. 


If the model is correct, then how to conceal these observations?

The model can explain most of the observed deformation which lead us to conclude that the main source of deformation observed by InSAR during the timespan is the elastic response of the upper crust to the water-level drop. Since there are no observations where other deformation mechanism effects are expected, we cannot conclude these are not present or active, but we consider their effect to be neglected away of the transform, compared to the one we model. 

You  mentioned the similarity between topography and InSAR pattern beyond the edges of the Dead Sea. (See figure attached).

One of the challenges in this research was to overcome the correlation between the topography and some of the sources affecting the InSAR measurements (e.g. topographic signal and stratigraphic atmosphere). We think we are demonstrating there is no correlation between topography and the observation/model. If there was correlation, the deformation pattern would be much different outside of the basin area.

Are these vertical isostatic displacement purely elastic? or a part of this deformation stay in the crust as permanent uplift counteracting subsidence at longer time-scales?.

The model assume purely elastic rebound. There could be a long-term visco-elastic effect, but it is beyond the time-scale of the observation to determine. Please see an example of such effect in:

Cavalié, O., M.-P. Doin, C. Lasserre, and P. Briole (2007), Ground motion measurement in the Lake Mead area, Nevada, by differential synthetic aperture radar interferometry time series analysis: Probing the lithosphere rheological structure, J. Geophys. Res., 112, B03403, doi:10.1029/2006JB004344.

and:

Doin, M.-P., C. Twardzik, G. Ducret, C. Lasserre, S. Guillaso, and S. Jianbao (2015), InSAR measurement of the deformation around Siling Co Lake: Inferences on the lower crust viscosity in central Tibet, J. Geophys. Res. Solid Earth, 120, 5290–5310, doi:10.1002/2014JB011768.

I hope this answers some of your questions and help clarify the apparent contradicting motion directions. Think of lifting a sand chunk at the beach with your hands. The whole chunk will be uplifted, but there will be local deformation and possibly subsidence at the center of the chunk. I know its not the best analog (e.g. not elastic at all) but can demonstrate how uplifting can coexist with subsidence.

Cheers,

Ran

Is the Dead Sea uplifting or subsiding? - ResearchGate. Available from: https://www.researchgate.net/post/Is_the_Dead_Sea_uplifting_or_subsiding [accessed Feb 21, 2017].

http://specialpapers.gsapubs.org/content/401/15.abstract

http://onlinelibrary.wiley.com/doi/10.1029/2006JB004344/abstract

http://onlinelibrary.wiley.com/doi/10.1002/2014JB011768/abstract

The Dead Sea water-level has been dropping at an exceedingly increasing rate since 1960...For details log in @ http://onlinelibrary.wiley.com/doi/10.1029/2011JB008961/full

http://onlinelibrary.wiley.com/doi/10.1029/2011JB008961/full

Dear Ran thank you very much for your complete answer ans sorry for my late reply, I have been since the last weeks in Israel working in the Dead Sea.Your comparison with sand chunk  is very clarifying, and due the long wavelength of the deformation pattern is less probably that this deformation may be due activity of local structures. I have been investigating similar scenarios, and I found similarities with the Lake Bonneville and Salton Sea both areas  undergone isostatic rebound like the dead Sea and, these oscillations have been related with activity of local structures, would be interesting to explore similar link in the Dead Sea as well. Thanks also for the bibliography. I hope  keep in touch for further discussion in the future.

All the best.