 eEQP-2024: eEQP-LinkedIn-3-PrecursorPhenomena |
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Earthquake Prediction (EQP) Research Based on the TRIZ Philosophy: |
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Toru Nakagawa (Emeritus Professor, Osaka Gakuin University） |
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Posted: Jul 21, 2024 |
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Editor's Note (Toru Nakagawa, Jul. 11, 2024)
This is the 3rd part of my introductory article on "Earthquake Prediction Research" posted on LinkedIn, especially in "TRIZ and Innovation" Group. This series is based, but further refined, on my presentation in Japanese at "Earthquake Prediction Society of Japan: Academic Conference 2023" (Dec. 22-23, 2023) (see
Abstract:
In current seismology, the physical conditions of various earthquakes (EQs) are not yet known, and thus the timing, process, and associated phenomena of destruction, i.e. the EQ, are not predictable. Therefore, research on short-term EQ prediction should follow the approach of "experimental science," which involves searching for possible precursor phenomena, selecting promising ones, and developing prediction methods by observing and analyzing the phenomena. We are now proceeding to the selection and development stage. The figure shows how we select precursor phenomena.
The first category is the mechanical phenomena. They include relative crustal motion, pressure, strain, etc., but they change too slowly to predict when the destruction will suddenly occur . Changes in the moving rate have been observed prior to EQs through analysis of geodetic satellite data (by Kamiyama et al.).
The second category are electromagnetic phenomena. They are generated as a secondary effect, but can be observed with high sensitivity by various methods; this is a well-known advantage of electromagnetic technology over mechanical ones. Various experiments have been carried out on the ground to observe electric fields, electromagnetic waves of different frequencies, radio waves reflected in the ionosphere, etc., but none of them was successful due to interference from various natural and artificial noises on the ground and in the sky.
The data of TEC (total electron content) in the ionosphere observed by GNSS satellite were analyzed by K. Heki to show an increase for a few hours before and after EQs. This method may be applicable to predict imminent large EQs on a global scale in the future.
M. Tsutsui observed the vertical electric field deep underground to detect drastic variations from a few hours before to several hours after an EQ. He obtained a continuous record of every second for an EQ (750 km distant, M6.8) with the S/N ratio over 30 and drastic fine structure. This method is epoch-making to clearly show the possibility of imminent EQ prediction inthe future.
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Earthquake Prediction (EQP) Research Based on the TRIZ Philosophy:
(3) For Selecting "Promising Precursor Phenomena"
[Click the figure to enlarge further.]
Using the criteria discussed in our previous post (2), we should next discuss the selection of earthquake (EQ) precursor phenomena that are expected to be promising as reliable/useful precursors in the future.
Before discussing the variety of precursor phenomena, we should reflect on the origins of the difficulty of short-term prediction of EQs.
(a) The accumulation of the EQ strain energy takes a long time, from several thousand years to several decades, while the EQs, i.e. the destruction with release of energy, occur in several seconds to several minutes. Thus, the timing of EQs is very difficult to know in advance.
(b) The physical situation near the epicenter is different, complex, and unknown.
(c) The rupture process, just before/during/after the EQ, is not well understood.
(d) The phenomena generated just before/during/after the EQs are not well understood.
--- In these situations,
we must first be prepared to search for various kinds of (precursor) phenomena, and
then we must select reliable/useful precursor phenomena
and develop the methods to measure and analyze the phenomena to predict the forthcoming EQs.
We should note that short-term EQ Prediction (EQP) research now faces the transition from the stage of searching for phenomena to the stage of selecting phenomena and developing methods.
The requirements for EQ precursor phenomena discussed in my previous post (2)are used here as the criteria for the new stage.
In the early stage, various phenomena such as anomalous behavior of animals, abnormal shape of clouds, change in underground water level, increase in radon radiation in the air, etc. are reported and studied.
The study of the anomalous behavior of animals may reveal their novel ability, but it will take a long time to turn such ability into a new technical system for EQ prediction.
Observation of underground water levels and radon radiation may not be widely useful for various cases of EQs.
… Considering these factors, I will not select them for further pursuit as candidates for precursor phenomena.
The top figure shows the categorization of various precursor candidate phenomena and the methods for observing them.
The top level shows the general categories of candidate phenomena, namely mechanical phenomena produced as primary effects, and electrical, magnetic, and electromagnetic phenomena produced as the secondary (or higher) effects.
At the second level, the phenomena are further classified in terms of their properties and their situations.
Then the third level shows their typical methods of observation, and
the fourth level shows some comments on the methods.
The first category consists of mechanical phenomena in general. Since they are the primary effects generated/observed in EQs, they have been studied much in history.
Horizontal/vertical movements of many observation points are measured, once with laborious trigonometric surveys, but recently with geodetic satellites in a much easier, systematic, and precise way. The relative motion of some points (or areas) with respect to neighboring points may cause EQs at some time in the future, but it is not known when.
Accumulation of such relative motion can be observed as pressure and strain in the crust deep underground. The sensitivity of volume strain gauges is on the order of 10 to the -9th.
--- These mechanical properties (i.e., motion, pressure, strain, etc.) can be observed to increase gradually and very slowly, but we cannot tell when they will reach the "unknown" threshold of disruption, namely EQs. This is the reason why EQs are only probabilistically foreseeable in the long/mid term and not predictable in the short term.
Short-term prediction may become possible only when some variation in the rate of change of such mechanical properties is clearly observed. The observation by M. Kamiyama et al. (2023) will be mentioned later.
After EQs, we often learn that we had a series of (smaller) "foreshocks" before.
However, when we have just had an EQ, current seismology cannot tell us whether or not a larger EQ, the "mainshock", will occur very shortly (within a week or a month).
To make such a judgment, we need to know whether some plate boundary or fault in the neighboring area can be triggered to suddenly release even larger energy of accumulated stress in a very short time.
--- Thus, in the current state of seismology, "foreshocks" (or several (small) EQs) are not reliable as EQ precursor phenomena.
The second major category of EQ precursor candidates is electromagnetic phenomena in general.
The piezoelectric effect converts the compressive stress of rocks in the crust into an electric field and further into various forms of electric, magnetic, and electromagnetic phenomena, although the details of the generation processes are not yet well understood.
This electromagnetic energy is much (probably several orders of magnitude) smaller than the mechanical energy.
However, various electromagnetic phenomena can be observed at any place by receiving signals from the whole epicenter area, resulting in significant signal energy.Electromagnetic technologies are much advantageous in detecting/measuring/analyzing the signals, in terms of versatile and sensitive methods in different modes, different frequency ranges, and at places even far away.
It is a well-known fact in history that science and technology have developed much by transforming from mechanical methods to electromagnetic methods. (The Creative Problem-Solving Methodology, TRIZ, emphasizes this evolution in technology.)
Various methods of observing possible electromagnetic precursor phenomena are subcategorized with the place of observation and the phenomena.
"On the ground" is, of course, the most popular and easiest place to observe.
Electric fields have been observed on the ground (or shallowly under the ground) to search for EQ precursor signals, but the attempts have not been successful because of the interference from natural and artificial noise.
Electromagnetic waves in various frequencies have also been observed to try to catch the signals coming from the epicenter region, but also not successful because of much disturbance by noise.
Another method observes FM waves from distant wideband stations, which are not directly reachable but from time to time detectable by reflection at intermediate ionosphere due to some changes in electric properties. Many cases of FM wave reflection have been observed, and after eliminating noise from solar flares, lightning, etc., they are attributed to reflections from meteors, airplanes, etc., but none to reflections clearly related to EQs.
--- In summary, attempts to observe various electromagnetic phenomena at ground sites to see the effects of EQs are mostly blocked by the abundance of unavoidable disturbances due to natural and artificial noise.
The use of GNSS satellites is increasing to observe the disturbances in the ionosphere that may be caused by EQs.
Variations in the Total Electric Content (TEC) of the ionosphere are observed in correlation with EQs (K. Heki, 2011, 2023). The method is found to be applicable almost worldwide for large EQs (M≧7) for a few hours before and after the EQ.
Observation of the electric field deep underground was reported by M. Tsutsui (2022).
He placed his DC dipole detector in a borehole 150 m deep underground in a remote, quiet place to avoid natural and artificial noise as much as possible.
Electric field signals from the epicenter area are detected directly through the geosphere with little chance of mixing with the natural/artificial noise on/above the ground.
Continuous observation with every second reveals the signals from EQs with a high S/N ratio and fine structure, covering a few hours before to several hours after EQs.
--- This report is (outstanding) epock-making with the possibility of Imminent EQ Prediction in the future.
Please see my next post.
Book Review Yoshida |
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Nakagawa Presentation (EPSJ 2023) |
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Last updated on Aug. 31, 2024. Access point: Editor: nakagawa@ogu.ac.jp
