NEW CHALLENGES IN EARTHQUAKE DYNAMICS: OBSERVING AND MODELLING A MULTI-SCALE SYSTEM.
Letter from Stavros T. Tassos; notes from the European Science Foundation Conference. (Posted with permission from the author).
Emphasis (bold) added by me.
Tassos, S.T., The ESF Conference, personal communication, received Nov 11, 2008
In the ESF Conference on ‘New Challenges in Earthquake Dynamics’ in Obergurgl, a small ski resort at 1900 meters altitude, and about 50 km from Innsbruck, Austria, some of the ‘big names’ among the about 100 participants, in the field of seismology presented their work. After the ESF conference I went to Leuven, for a lecture to about 20 PhD students and staff members. As an ‘observer’, but also as an ‘involved participant’ I will try to present the general themes and highlights of these two events, as well as their reaction to my ideas, and my reaction to their ideas.Kanamori, H., The Energy Release in Great Earthquakes, Journal of Geophysical Research, Volume 82, Issue B20, p. 2981-2988, 1977
-- Although the title of the conference was ‘New Challenges in Earthquake Dynamics’, the general framework of plate tectonics and elastic rebound was not challenged. Only my presentation titled ‘the challenge of the cause and effect relationship between faults and earthquakes’ challenged the fundamental assumptions of plate tectonics and elastic rebound.
-- The earthquake dynamics within the mainstream plate tectonics and horizontal movement framework refer to horizontal stress, mostly static, i.e., the one that does not change, or changes very slowly with time, but the horizontal dynamic stress, i.e., the one that changes quickly with time, was also considered and debated. Thus in the conventional framework rocks are an elastic medium, at least partially, and static stress changes along future fault planes produce elastic strain accumulation, i.e., bending, frictional sliding, then rupture, and finally an earthquake.
-- My thesis is that rocks are a plastic medium, i.e., they cannot accumulate elastic strain through bending, and an earthquake is the primary elastic mandatory effect of a sufficient dynamic stress, as in free-fall, from a height of the order of 10^-5 to 10^-2 m, that forces an otherwise inelastic medium to respond momentarily elastically, and a fault is the secondary possible post-seismic inelastic effect if the stress is sufficiently high to cause rupture. In other words I concentrate on understanding, and proposing a comprehensive and physically possible deterministic model of the physics of the earthquake source, and not on statistical modeling.
-- Within again the mainstream framework the validity of statistical models was discussed and debated. In one case an invited speaker presented the case of nine (9) different models that all fitted the data from a particular earthquake very well. It is obvious that most likely neither one of them corresponds to the physical actuality and all are mental artifacts. In all cases most of the work presented was on statistical models and on how static stress accumulates and transfers, and not about the physics of the earthquake source, which is still unknown as it was unanimously recognized.
-- The deadlock of the mainstream approach was shown on several occasions. I do not mention names, first because the views expressed by most if not all speakers more or less reflect the general feeling, and second because my intention is only to discuss and criticize ideas:
1.One of the key speakers presented his statistical model on how aftershocks can be triggered by either static or dynamic horizontal stress transfer from the main-shock. My question was: OK let us accept that the aftershocks were triggered by the main shock, but then what triggered the main-shock? Because if the laws of nature are the same regardless of frame of reference, as they are, and your model corresponds to the physical actuality the main-shock should be triggered by an even stronger, but unknown shock His answer was “I do not know. I have only made a statistical model about aftershocks”. I think this is one of the main weaknesses of the main-stream way of thinking. Isolate a case and build ad-hoc mathematically perfect statistical models, which nevertheless usually contradict other ad-hoc models, and most likely have nothing to do with the physical actuality.
2.On another occasion a speaker presented an interesting theoretical and experimental work on the effect of fractured rock on seismic wave velocity. Making also a statement, I asked him, that the real issue was if fracturing could produce seismic waves, and if he had done any experiment on that. His answer was that he had not done any experiment on that, but others had done. But, all those who have experimented with rock rupture under high confining pressure have only recorded sound waves, the speed of which is more than one order of magnitude lower, of the order of 340 m/sec, than the speed of seismic waves, and of course they are transmitted in the air, not in solid rock with about 10^11 Pa rigidity. On the contrary as it was shown experimentally with projectile impacts by Freund (2002, 2003), at 1.45 km.s^-1 impact velocity, P and S waves propagating at ~6 and 3.4 km.s^-1, respectively, were generated that soon faded away within 0.2 ms after impact. At 4.45 km.s^-1 impact velocity fissures began to form 2 ms after impact, i.e., ten times later in time after the seismic waves faded away, and at 5.64 km.s^-1 the block ruptured into three segments along the formerly formed fissures. Thus the dynamic stress had two effects; a primary and a secondary. The primary is mandatory and co-seismic, and refers to the transient elastic response of an otherwise non-elastic rock block, and the generation of seismic waves. The secondary is possible and post-seismic, and involves inelastic slip and the generation of a fault, and occurs there and when the rock’s strength has been exceeded to the degree to cause rupture, and not only creep or slip.
3.Nevertheless few scientists, especially the younger ones but not only, in their private discussions with me expressed a view which could be summed up as “you got a point”.
4.On the overall, the reaction of the majority to my proposition and my reaction to their reaction in both the ESF conference and Leuven University is contained in the e-mails exchanged by Prof. Rudy Swennen, at Leuven University and myself after my talk there. They are as follows: «Dear Stavros, Thank you once again for the nice presentation. Your presentation certainly stimulated some of the discussion in my department, however most scientists are very sceptical about most of your ideas. Kind regards, Rudy», and my reply: «Dear Rudy, It was my pleasure to meet you again and to present my ideas to your department. The reaction of your colleagues is the expected one, and more or less typical of geological audiences, whereas the engineering audiences are more receptive. Of course I insist on my ideas, because I did not hear any scientific objection, for example about the earth's interior getting more rigid as depth increases, because otherwise the observed seismic wave velocity increase with depth cannot be explained. If this is a fact, as I think observation and logic indicate it is, the implications are unavoidable. For one thing the ambient temperatures in the mantle cannot be high, and more so increase with depth. Therefore although I can understand the psychological reaction because I put under question literally all the fundamental assumptions and notions of mainstream science, I cannot consider it equivalent to a scientific argument. I try to come up with a comprehensive set of ideas so that there is no need to adhere to ad-hoc interpretations that usually contradict each other, for example treat the earth as a solid body in seismology, and as a melt in volcanology, in order to explain the various physical phenomena. Nevertheless I really appreciate the opinion of people like you. So since you have my presentation, and of course at your early convenience, study it, reflect on it, and then I would be more than happy to hear your scientific objections, and try to answer them. Thank you again for the invitation to present my provocative ideas to your department. Best regards, Stavros»
Freund, F.T., et al., Mid-Infrared Luminescence Observed During Rock Deformation, AGU, 2002
Freund, F.T., Rocks That Crackle and Sparkle and Glow: Strange Pre-Earthquake Phenomena, Journal of Scientific Exploration, Volume 17, Number 1, Pages 37-71, 2003
Freund, F.T., et al., Stimulated IR Emission From The Surface of Rocks During Deformation, AGU, Volume 84, Number 46, 2003
Tassos, S.T., and Ford, D.J., An Integrated Alternative Conceptual Framework to Heat Engine Earth, Plate Tectonics, and Elastic Rebound, Journal of Scientific Exploration, Volume 19, Number 1, Pages 43-90, 2005