A8. Report on 2011Earthquake in Japane

Investigation of the forces responsible for the Earthquake in Japan 11 March 2011

Project Engineer R. Maurer MSc CEng F. InstMC

Information received 18 July 2020. Japan trench (2) Marianna trench (3, 4, 5 pp, 6pp) Diagrams of faults & (7) video showing the March 11, 2011 Earthquake movement sequence

The sketches (3, 4, 5, 6) show with various explanations the fault scarps off Japan as it faces eastwards towards the Pacific Ocean. This observation helps give credence to the proposition that the continental crust is driven over the Pacific oceanic crust as distinct from subduction of the oceanic crust under the continental plate. The video (7) shows the individual directional movements of the four major Japanese Islands immediately before, during and after the earthquake.

lateral movements ☆fixed point.wmv

This investigation is to try and determine if the circumferential forces related to the rotational velocity of the earth have a direct effect on volcanic and earthquake activity on the Japanese and Philippine island arcs. At present the Atlantic Ocean is expanding at the expense of the Pacific Ocean into which the American plates are moving from the east and the Eurasian plate is moving in from the west. Under ideal conditions, the subduction of the oceanic crust should be balanced by its production elsewhere on the planet. However, the Heezen -Tharp 77 map, despite its limitations does show a very crumpled Pacific Basin east of the Eurasian plate and west of the Hawaiian -Emperor volcanic chain. This area has the appearance of the ocean floor being under compression. The slow but relentless ingress of the Australian plate may also be adding to the magnitude of compression Under these circumstances the Pacific basin convergent margins are put under compression. The latitude -aligned Aleutian trench fracture in the northern Pacific is presently explained as being due to the subduction of the Pacific plate under the North American plate.

Prior to the earthquake, the video shows the displacement arrows across the Japanese chain from northern Hokkaido down to Kyushu pointing northwest. However, to the south along the Okinawa trough, the displacement arrows point south east. The change in the direction of the displacement arrows to an anticlockwise movement is first noted on Hokkaido at position ‘8’. At ‘6’ the displacement arrows at Kyushu start to turn clockwise. At this juncture both ends of Japan appear to be taking on an ‘S’ shape. At position 2.5 the bottom two islands of the Japanese plate are starting to turn clockwise in opposed to the anti-clockwise movement of Hokkaido. The above-mentioned movements at both ends of the Japanese arc would put Honshu under a severe bending moment which will result in fracture in the direction of the bend and the sudden outward movement of a segment of Honshu island. This action is similar to the breaking of a cane as it is bent into a hoop

Alternatively, and the most probable explanation (as shown below), is that the Japanese arc is being pushed eastwards, with Honshu moving preferentially eastwards. As Honshu with its fault line is moved forward the adjacent islands will turn inwards, one end turning clockwise and the other end anti-clockwise. In the engineering world, this is what the stress pattern may look like when sheet steel is deformed on being punched into a depressed square type ‘U’ shape such as a basin.

This preliminary investigation will consider the possible sources of the eastward push of Japan.

The area in question is stated as being approximately 300 km long by 150 km wide: it lurched 50 metres to the east-south-east and was thrust upward about 10 metres.

Fig A.8.1

Brief Google literature survey on the evolution of the Japanese and Eurasian plates

Rather than simply accept that subduction by the Pacific basin under Japan as the prime cause of the earthquakes on the mainland, it was decided to investigate the possibility that faulting within the Eurasian plate may have a greater effect than hitherto anticipated. As such it was decided to first investigate the historical makeup of Laurasia to look for areas of possible crustal weakness.

Laurasia was the combination of Laurentia and Eurasia during the Carboniferous. During that period, Eurasia comprised Baltica, Siberia, Kazakhstania and N & S China and peri-Gondwanan microcontinental blocks. Previously, in the Devonian, Laurentia was combined with just Baltica and the peri-Gondwanan blocks as Laurussia. Siberia, Kazakhstania and the Chinese blocks were still separate at that time. In the late Carboniferous, Gondwana amalgamated with Laurasia to become Pangaea. Laurasia split into North America (including Greenland) and Eurasia when the North Atlantic opened from the late Cretaceous into the Paleogene (about 80 Ma onwards). The Central and South Atlantic were well developed by this time. At the start of the Miocene (23 Ma), Japan was part of Eurasia. By 15 Ma, as the Sea of Japan opened, Japan was pivoting away from China but still attached to it (as a peninsula) at the southern end. This end of Japan (Kyushu) separated from China in the late Pliocene. Hokkaido was uplifted from below sea level. For Japan to move (or pivot) away from Eurasia it must have been moving at a faster rate. (Section researched by Allan Wheeler)

Looking at the main Japanese islands, at present, the northern island of Hokkaido and northern Honshu are on the Okhotsk plate; southern Honshu, Shikoku and most of Kyushu are on the Amur plate (a sub-plate of Eurasia). Northern Honshu and Hokkaido are bounded by the Pacific plate to the east and southern Honshu and the southern islands are bounded by the Amur plate to the west and the Philippine Sea plate to the east, which is in turn bounded on the east by the Pacific plate. The plate boundary between Amur and the Okhotsk plates cuts through the central part of Honshu island. The boundaries between the North American and Okhotsk plates are now deemed to be separated by a strike slip fault. The exact position of the plate boundary between the Eurasian and Amur plates has still to be agreed.

Fig A.8.2

Fig A.8.3

Fig A.8.4: Regional map showing the location of the Baikal Rift Zone in southern Siberia and the associated lithosphere plates and microplates that compose the tectonic framework of central Asia. The dashed square marks the study area of the BEST project. After Zonenshain and Savostin [1981] and Moore et al. [1997]

The Rifts in the Eurasian plate that are possibly associated with the 2011 Earthquake

Despite various theories/claims including one that cites the slippery clay lining at the fault boundary was the cause of the earthquake, the change in the direction of the displacement markers as noted on the video shows that significant forces are needed to twist an Island chain like Japan. As such several alternative possibilities need to be considered.

  1. The late Cenozoic Baikal Rift Zone (BRZ) in southern Siberia is composed of several individual topographic depressions and half grabens with the deep Lake Baikal at its center. A 350km section of the 2000 Km long feature has been interpreted as resulting from mafic intrusions. It is also suggested that the BRZ is formed by passive rifting in the rheologically weak suture between the Siberian Zone and the Amur sub-plate. The BRZ is one of the four major Cenozoic continental rift systems, and it shows most of the characters associated with continental rifting: elongated sedimentary grabens, elevated margins, volcanic provinces, normal faults, and high seismic activity. The BRZ one of the most seismically active continental rifts in the world.

  2. It is also suggested that ‘Intracontinental rifting is assumed to be the initial stage of a development, that eventually may lead to breakup and separation of lithospheric plates and formation of new oceanic plates, unless extension ceases and the evolution changes into formation of wide sedimentary depressions or grabens' [Turcotte and Emerman , 1983; Olsen and Morgan , 1995]. Although this feature is 2000 km from the Okhotsk plate it nevertheless butts up against the intermediate Amur plate.

  3. More importantly extension rifts which are not a function of subduction are evident along the Eurasian plate from Iran to China. This was noted in the webinar given on June 30, 2020 by Prof Richard Walker of the University of Oxford.

Earthquakes of the Silk Road – reinterpreting the historic and prehistoric ruptures of central Asia. Summary of Extract given below

In contrast to plate boundaries, where earthquake hazard is usually confined to narrow zones around the edges of the oceans, active faulting within continental interiors is spread across very wide regions, and with intervals of hundreds, or even thousands of years between large earthquakes in any one area. The long recurrence intervals in continental interiors poses challenges for the identification of active faults, and means that we have ancient and modern, across the interior of Asia. Our study encompasses a region spanning from Iran in the west, through the ex-soviet Central Asian republics, to China in the East. Many of our large late-historical examples are from the Tien Shan region of central Asia, as represented by the cluster of earthquakes in 1887, 1889, and 1911 in the vicinity of Almaty, Kazakhstan. These examples allow us to address the relationship between rupture length and amount of slip, and the potential for large earthquakes to occur due to complex rupture across multiple short faults. Many of the prominent faults of central Asia have no documented historical record of earthquakes near them, and yet display evidence in the landscape for rupture in the recent past.

  1. Development of stress faulting and continental plate elongation by radial forces

In the same way that the Atlantic ocean/basin is growing at the expense of the Pacific basin by the westward movement of the American plates, the Indian Ocean is also growing at expense of the Pacific Ocean by the slower eastward movement of the Eurasian plate. In its eastwards movement the Eurasian plate has to move along a tortuous elongated area latitude boundary between 150 and 600 N, This would involve the stretching of the fluid viscous mantle into thinner but nevertheless continuous section and the cracking of the brittle oceanic layers. The paper given by Dr R. Walker (noted above) describes many such faults and volcanically active regions along the major plate.

Although the distances involved with these faults and their extensions are small, the total integrated extension may in fact be of significant proportions to push against the Japanese and Philippine island arcs at the Pacific end of the Eurasian plate. The frictional resistance offered by the forcing down of the oceanic crust would put the converging margins under compression with the resultant cracking perpendicular to the line of force. If the cracking extends down to the mantle, then magma will issue forth as volcanoes. Ultimately it would appear that the oceanic crust underlying the Sea of Japan would absorb any elongation by rifting caused by the geometric changes of the Eurasian Plate.

Fig A.8.5

Fig A.8.6: After Heuret and Lallemand (2005)

Fig A.8.7

5. Possible force exerted on Honshu by rollback (Heuret and Lallemand (2005)

The Japan sea basin could also be extended by the slab rollback mechanism. This extension occurs where a denser older slab begins to sink relative to the overlying plate as depicted below in the figure. Heuret and Lallemand (2005) show several variations which would result in back arc extension and rifting. The illustration shown is based on their work

6. Differential circumferential stress in the Earth’s rim

The calculated differential circumferential stress induced in the Earth’s rim by considering the centre of mass of the Earth being off centre from the principal axis of rotation by as little as 1km in the 6400Km radius, will have sufficient force to push the American plates westward and the Eurasian plate eastwards towards the Pacific basin. The rotational velocity based radial forces will add to the eastward aligned circumferential forces in trying to both move and elongate the Japanese Sea basin latitudinally in an easterly direction. This action would be felt all along the western edge of the Japanese Island Arc which would be pushed eastwards and which in turn will cause stress faulting in the underlying oceanic crust.

At present the geological structure and composition of the islands are not fully mapped and understood. A major complication in understanding the make -up is occasioned by the islands being formed at different times and thus having different ages. Furthermore, the younger plates with greater volcanic activity appear to face the oceanic basin while the sides facing the Sea of Japan show evidence of heavy faulting and sedimentation. The presence of thick Quaternary accretionary deposits inhibits the study of the complete make-up of the Japanese Island system, but gravitational anomaly mapping, seismic surveys and borehole evidence can make up for this. Understanding may have advanced by the time of the publication of 'The Geology of Japan' in 2016, which updates research done 20 years ago.

It is this very make up that allows a constant force applied to the whole western side of Japan to preferentially move the weakest parts the furthest distance, This process is likely to continue until such time as the Island system is either completely broken up or welded into a unitary configuration. The question arises if the islands are connected at depth or are independent terranes. Furthermore, were the islands connected when the sea level was up to 120m lower during the Quaternary ice ages? Under these conditions the associated push force would be sufficient to force the Japanese island eastward. The circumferential forces would meet little frictional resistance at the Izu Collision Zone from where the Honshu island could lurch forward thus creating the Earthquake.

7. Discussion and Conclusions

The absence of detailed knowledge by the author of other major earthquakes both along the convergent margins and along the central Asian complex on the Eurasian plate makes it difficult to offer general conclusions regarding the forces responsible for earthquake activity.

It is also difficult to reconcile what appears to be a variable direction subduction process of the oceanic plates as being solely responsible for all the earthquake and volcanic activity along the Pacific basin rim. This area is generally referred to as the Ring of Fire. The conclusions and discussion points offered are thus limited in scope and subject to correction.

The first indication that the continental crust is moving over the oceanic crust is given by the eastward facing scarps of the Japanese arc. Using this as the starting point, various tectonic activities were investigated to determine their contribution to this situation.

  1. The variable shaping of the Eurasian plate by extension or compression as it is being pushed eastwards by its passage through different diametral surface areas of the bulge is unlikely to be translated as a physical push force against the Japanese arc. The oceanic crust of the intermediate Sea of Japan would most likely absorb the limited preferential extension by possibly buckling and cracking and possibly give rise to magma intrusion. However, this action of stretching and/or compression may be considered as a prime force for the opening of the Baikal and other rifts on the central Eurasian plate as noted by Dr R Walker.

  1. Extension of the Sea of Japan by Rollback

The observation on the Heezen-Tharp 77 oceanographic map which displays a very cracked and crumpled Pacific oceanic crust, makes the Rollback action a probable source for initiating earthquake activity. The faults (Figs,3,54,5,and 6) induced in the subducted oceanic crust whilst being forced under the continental crust can obviously lead to segments breaking away and causing rollback , The absence of detailed information limits the discussion on this point. Collaborative evidence is needed to pursue this line of discussion

  1. Circumferential Rim Forces

The video (Fig 7) suggests the earthquake occurred after a sustained 14-year application of an eastward ‘push’ force over the whole of Japan’ This finally caused the weakest held section Honshu to move the furthest eastwards.

Historically, Japan which was part of Eurasia pivoted away from China at the southern end as a peninsula and the Sea of Japan opened c 15 Ma. Kyushu separated from China in the late Pliocene. Hokkaido was uplifted from below sea level. It is thus feasible that the circumferential forces treated this Japanese section as a separate entity and being smaller it was able to respond by moving at a slightly faster rate than the main Eurasian plate. This point is partly speculative and open to argument as the variable speed movement would need to be accompanied by a simultaneous variable speed subduction process in the same direction. However, a unidirectional circumferential driving force will move objects at different rates depending on the frictional resistance Bearing in mind the continuous westward movement of the American plates and the continuing eastwards albeit slow movement of Eurasia with its fault lines that cannot be attributed to subduction, the most likely force triggering the earthquake will be the circumferential rim force.

Technical Notes used as an aid to the understanding of the processes involved

  1. Centripetal, Differential Circumferential and Convectional forces

Although both named forces are related to the rotational velocity of the Earth, they play different roles. To avoid continuously explaining the differences between centripetal and centrifugal forces, the use of the term Radial force is introduced.

The radial force that is responsible for the earth’s bulged/oblate shape is credited with forcing and spreading the crust into the maximum surface area. In contradiction the circumferential forces are credited with the movement of the continental plates from the heavier to the lighter side of the earth. Presently these movements are east and west of the present African plate. The use of Earth changing forces being related to the rotational velocity of the Earth allows for explanations that are derived on clearly defined unidirectional actions

  1. Shear

The following section on Shear extension is copied from - (Tectonic Evolution of the Japanese Island Arc System -by Ashiko Taira. https://www.gsj.jp/en/ (Geological Survey of Japan). At this early stage, only the major reference works are noted stage.

6.4. Pure or Simple Shear Extension

[53] The evolution of continental rift structures can be explained by three stretching mechanisms: pure shear, simple shear and combined pure shear and simple shear [Ruppel , 1995]. Each mechanism produces its own pattern of thermal evolution, basin formation, subsidence, uplift and sedimentation [Ruppel, 1995]. In the pure shear model, defined by McKenzie [1978], the stretching of the lithosphere is considered to be uniform. Since the upper crustal extension is directly overlying the site of thinning in the mantle lithosphere, the extension pattern of the pure shear model is highly symmetric. In the simple shear model, the lithospheric extension is accommodated along a major low‐angle detachment fault or shear zone which cuts through the crust and mantle lithosphere [Wernicke, 1985]. The spatial distribution of extension in the simple shear model is asymmetric because the extension of the upper crust is laterally displaced in relation to the extension of the mantle lithosphere. In the combined pure shear‐simple shear stretching model, the upper brittle part of the crust is deformed by simple shear, and the ductile lower crust and mantle lithosphere is deformed by pure shear [Coward, 1986]. BEST (Baikal Explosion Seismic Transects)’.

Earthquake locations for events between 1965 and 1995

Notes by Prof. Shigeyuki Suzuki Sent: 18 July 2020 02:11

Dear Bob, I have made simple figures on Pacific trench.

On the ocean side of Japan trench, we have distinct scarps of extensional normal fault. It indicates oceanic crusts do not push continental crust.

The Mariana trench also has the same structure. The figure with extensional faults is found on the internet.

I made a simplified cross section of the trench. Thrusts are developed at the toe of continental crust because continental crust pushes actively to the ocean ward. On the otherworld, oceanic crust has extensional faults. The profile with epicenter indicates that many small earthquakes happened in the area of normal faults.

But the normal faults dips ocean ward not trench ward. I think I can explain why. So, I attached a simple figure. Continental crust moves to the ocean ward by the effect of the rotating earth. Continental crust rides on oceanic crust. The thickness of the toe of continental crust is increasing. By the effect of isostasy, the area of deep trench is a little floating. The floating movement could make the normal fault with the subsiding ocean side.

Discussion of Information given to R. Maurer. See attached explanatory PP illustrations below.

Note 1

I have been thinking about the slides and propose that Flexure of the subducted plate creates extension, hence normal faults are generated with majority downthrown to the east, opposite in motion to the plate forced under Japan to the west.

I also attach here a powerpoint to illuminate the idea.

Note 2

I have reviewed the illustrations sent to R. Maurer and observe that there are normal faults downthrown to the east and located oceanward to the east to the east of the subducting oceanic crust in both Japan and Mariana Trench examples. I had not seen that phenomenon before. As you know, I am not a structural geologist but envisage that the stress regime that has resulted in this unusual setting could be analysed with the use of a stress ellipse. The normal eastward heading faults could be a relaxation phenomenon after a push of the oceanic crust towards the west. Perhaps one of your structural contacts could assist in this.

The move clip is interesting, and I assume that it is a synopsis of structural vectors measured in Japan through recent times. However, I cannot read Japanese and there is no commentary to accompany the movie. Perhaps Prof. S could provide an explanation.

Your centripetal forces theory could help to explain the motions of the crustal plates, but a detailed area specific study will be required.