Dear Dr. Desai,

it is not an easy task to differentiate between the two types of soft-sediment deformation. You have to take a closer look at the sedimentary features and also keep an eye on the overall-geodynamic setting, in other words: Is the region prone to earthquakes?

I attach 2 papers, one from the "Lesser Himalaya" and another from the "Dead Sea Transform Fault"  where the so-called seismites are shown and proven by the still lingering seismicity.

The question is still unanswered. What triggered such beds and made them show up in stacked patterns of convoluted bedsets others than tremors and shock waves caused by  seismic pulses ?

Slumps and soft-sediment deformation in shale-hosted metal deposits and flysch sediments may at the very end also be related to such processes

I hope it will help you.

Best regards

Harald G. Dill

Dear Dr Desai,

It is a complex topic, and there are several papers dealing with this problem (see links below). Many researchers differentiate triggers that are related to sedimentary processes (called autogenic/autokinetic, such as the action of breaking and pounding waves, shear stresses and turbulence related to subaqueous currents, such as tides, rapid sediment loading, glaciotectonics, groundwater seepage, and biogenic processes) and allogenic, or external, triggers (such as earthquakes). Deformation features formed by the former processes should show a connection between the sedimentary facies and the occurrence of sedimentary deformation features. Such linkage is non-existent in the case of external triggers.

To deduct a most likely trigger one should study the deformation features (morphology, deformation mechanism, rheology of sediment upon deformation, and timing in terms of burial, etc.) and the sedimentary facies (sedimentary processes, environmental factors - e.g. degree of slope, likely autogenic triggers). Earthquake-triggered deformations are expected to be laterally extensive, but deformation is controlled by rheology and, as such, deformation might affect specific facies and die out laterally (good examples are the modern EQ-induced liquefaction features affecting only channel sands on floodplains in Japan or New Zealand). There are also autogenic processes that may affect large areas, and, thus, deformation can be extensive. In a low-energy, low-gradient (

I think if we locate the deformations along lithostratigraphic units, we can have two cases : i) deformations related to one unit (formation or member) and ii) deformations related to several lithostratigraphic units. The sismogenic source must be rapid (discontinous) in time but longevity of the sismic source make that several units are affected by deformation.

In other way, if the geographic correlation shows that the deformations are limited to one formation and very extend geographically, it may be related to load causes. The essential features may be the discontinuity in time but longevity of the sismic source compared to ponctual deformations (slides, collapse, loaded strcutures....)t hat affect only restricted lithostratigraphic unit that may be related to burial causes.

Dear Dr Desai,

An interesting question - and a difficult one to answer! The main points have already been suggested - look at the overall context of where the soft sediment deformation (SSD) occurs in relation to a) seismicity, b) palaeogeography (and angles of slopes), c) stratigraphy and sedimentological variations. SSD is much easier to analyse in younger settings as some of these unknowns and variables are better constrained. Some recent work in the Dead Sea Basin where seismicity along the Dead Sea Transform causes SSD in late Pleistocene sediments is attached. This is one end member where there is good control on the causes of deformation ( slow sedimentation, very low angle slopes, but high levels of seismicity) and has therefore been treated as a case study of seismogenic deformation.  

Article Soft-sediment deformation within seismogenic slumps of the D...

Article Seismogenic slump folds formed by gravity-driven tectonics d...

Try magnetic methods as discussed in the paper below.

best wishes

Nils-Axel Mörner

Dear Dr Desai,

You mention a great issue!

I would also recommend magnetic methods, especially magnetic susceptibility tests. In addition i provide to you one paper which i think would be very helpfull to you.

Best regards, Spiros Sergiou

Dear Dr. Desai,

As others have commented, indeed an ambiguous problem. To a large extent, the answer to this is in my mind 25% subjective and 75% objective.

Primarily, for any soft sediment deformation to be linked to seismicity, it is necessary to show that there is an 'active fault' in the vicinity in the first place.

For ancient sediments (as against Recent / Holocene sediments), the demonstration of active faulting during the sedimentation history of the horizons becomes difficult. Very often it has to be conjectural and hence becomes subjective. I may be convinced, but the next person need not be.

It is more logical to conclude that the SSD features demonstrate 2 clear things (1) that the compaction history of the sediments was not a smooth one, rather one where abrupt disruptions took place and (2) that the sedimentation rate was rapid, to enable entrapment and lithification of the SSD horizons within undisturbed horizons.

I add two of my students' works that may help you and may also provide you with some citation links.

Best wishes,

Start with a reference book such as Maltman (1994). Myself, I have published only on seismogenically-triggered soil liquefaction. Mörner has published an entire book full of pictures on swedish Holocene liquefaction, for which I contributed. The magnetic properties is an answer (look at Beck's and Mörner's work). Obermeier has largely discussed the subject!!!!!

One technical way is delineated in the linked paper

https://www.researchgate.net/profile/Amotz_Agnon/publications?sorting=newest&page=4

All the mechanisms mentioned here (I am not specialist) could be accompanied by another specific effect of seismic areas, given by the transformations produced over time by electric currents of the electrical / electromagnetic fields, of ultra-low frequencies, generated by the high values ​​of tectonic stress from seismogenic and adjacent areas.

Perhaps the changes are small in the short term, but in a long time the circulation of these currents would have unexpected consequences. For example, after 20 years of uninterrupted functioning of a small electric cell consisting of two different electrodes (a few centimeters long and 1-2 mm in diameter), initially situated in sand saturated with water, it was necessary to destroy the glass vessel because the sand had become dry and with a gritstone look (!). Everything under laboratory conditions! I'm really curious if there are references to the electrical aspect of your problem.

The more basic question may be as to which soft-sediment deformation is tectonic and which is non-tectonic at all. Read this paper in the attached info.

Interesting question, and the solution of this problem is probably through having sufficiently large observation scale to observe the SSD either related to faults or to non-tectonic local dewatering. The latter can be in the form of subsurface water flow, locally compacting sediment etc. If the SSD is related to package sliding, as occurs on subaqueous slopes of deltas and submarine fans, I think one must ask whether the sliding results from tectonics or from local liquefaction (due to wave loading, rapid deposition etc.) and merely consider the dewatering as a consequence of the slide event.

An interesting and commonly asked question on SSDS is that by looking at a single structure, whether we will be able to classify it to be seismically or aseismically generated. One word answer would be 'No'. Professor George Postma mentions in his comment that the scale of observation has to be large in order to identify the correct trigger agents (seismic or seismic), that is, a detailed facies analysis of the Formation within which the SSDS are present and the tectonic history of the basin, must be evaluated in order to interpret the correct mechanisms responsible for the formation of SSDS, the driving forces for the development of the structures and the trigger agents. Using facies analysis as a tool, the mechanisms and the driving forces must be identified first. Then based on the facies analysis, using the process of logical elimination, the trigger agents responsible for the development of the structures in the study area must be identified. Thus, only after a detailed review of the seismic and aseismic trigger agents in the study area, we can conclusively establish the origin of the SSDS. I am attaching our paper which will help in understanding the methodology to review the triggering agents.

It has increasingly been popular to identify deformation structures as due to seismicity, yet uncritically. However, some of these structures are deep with sedimentary succession that are consolidated. Notably often the deformations do not extend upwards or downwards through bedding planes. Major deformation should disrupt bedding planes. Restriction of deformation to individual units only indicates that deformation was shortly after the deposition of the unconsolidated unit. Consolidated sediments cannot readily deform but slowly, but will fracture if subject to significant seismicity. Many so-called seismic-induced deformation structures are due to local gravity slumping, rapid loading from above due to rapid sedimentation, or stressing due to fluid overflows or debris flows etc when the sediments were still very wet and unconsolidated. Seismicity can result in slumping of recently deposited unconsolidated sediments on steep slopes which may load sediment deposits down slope. However, it is very unlikely that seismicity will significantly deform deeply-buried unconsolidated sediments where lateral and vertical movement is inhibited by sediment mass.

As noted by the previous posts, its very difficult to determine if SSD structures were created during seismicity or by other processes. What is becoming apparent is that deformation linked to downslope movement (potentially triggered by seismicity) may form within the buried (but unconsolidated) sedimentary sequence as well as at the sediment surface. Criteria to distinguish surface versus sub-surface deformation of soft-sediments have been catalogued and described in a publication (free to download) at: https://authors.elsevier.com/a/1eHcbhdGqYvIw

Thanks

Ian

Numerous possible trigger mechanisms have been described for SSD structures. The most known are (i) sediment loading (ii) turbiditic currents, storm current (iii) collapse structures (iv) liquefaction through preexisting cracks (v) seismic.

The SSDS can be formed by all these five trigger mechanism. For conclusion need to study these all trigger mechanism broadly and the close interpretation of all SSDS is required.

Article Soft Sediment Deformation Structures in Quaternary Sediments...

It is not easy answer, but probably it depend on water saturated within the sedimentary rock..

Apparently, from all the feedback, the answer would be: no, nobody has a reliable diagnostic criteria. If we focus on soft sedimentary deformation structures strictly caused by shock waves from seismic events, perhaps it would be a good idea to focus on microfacies analyses. Maybe there are some textures and grain-to-grain spatial relationships that are only produced by any of the body and surface waves. Maybe someone has already looked at that??