The 2005 modification of GIT geologocal map of the ocean floor - an effective tool for the prediction of the most powerful earthquakes
Published in: Institut Cartográphic de Catalunya, Institut Geológic de Catalunya, 5th Europan Congress on Regional Geoscientific Cartography, Barcelona, 2006
A broadened version of the original paper is presented below.
Correlation between powerful earthquakes and the distances from their epicentres to the ocean floor isochrones
N. Parubets Granton Institute of Technology, 263 Adelaide Street West, Toronto, M5H1Y3 Canada, nicolas.parubets@gmail@com
Abstract: An overall analysis of the occurrences of the most powerful registered earthquakes – of a magnitude 8.5 and higher – makes it possible to trace the geological similarity of the areas where they appear. Namely, all of them occurred at the continental crust or at least at the very edge of it. Significantly, most of them occurred near very specific parts of the subduction zones, just where the oceanic floor’s isochrons corresponds with magnetic anomalies 29, and the continental crust meet, or where the Mesozoic crust, and Cenozoic crust are nearby.
Table 1 presents an up-to-date list of the most powerful registered earthquakes (MPREs) and shows the approximate distances from their epicentres to the nearest Mesozoic oceanic crust (chron 29 and progressively higher chrons) and Cenozoic oceanic crusts (chron 29 and progressively smaller chrons), and also distances to the edges of the continental crust.
* Compiled from UNESCO GMW (UNESCO, 2000); GMOF 3rd Ed. (2008 Modification of GMOF, 2008); PDE (2008); Bolt (1993); Kanamori (1997); Lomnitz (1994)
** Any data related to earthquake magnitude prior to the introduction of the Richter scale were commonly evaluated using other scales or by calculations stemming from the observed destruction, which were often inaccurate. Only two such earthquakes are listed in this table
*** Disputed magnitudes
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Fig. 1 – The 2008 modification of the 2004 Geological Map of the Ocean Floor (2008). The map includes bathymetry of the ocean floor, chronostratigraphic ages of the oceanic crust, locations of MPREs, and the areas with the highest probability of MPREs in the foreseeable future.
In addition, Fig. 1 provides an opportunity to visualize the above mentioned conformities, such as the relation between the localities of the MPREs and their distances from some of the planet’s geological structures, particularly from the subduction zones and from the Mesozoic and/or Cenozoic oceanic crusts.
The proposed way of classifying the MPREs reveals that almost 65 percent of them did occur near – from 25 km to 750 km – areas that have a specific geological similarity, that with the presence of oceanic floor’s magnetic anomaly 29 (Müller, 1997; McElhinny and McFadden, 2000), and where there are subduction zones nearby – from 100 km to 325 km (category I in Table 1). Significantly, all of the MPREs occurred at the continental crust.
A total of 16 of the 17 most powerful registered earthquakes did occur at or under the continental crust, and only one, that is, off the coast of Ecuador in 1906, happened at the oceanic crust (Fig. 1). There is a question about whether the 1906 data is accurate. Earthquake detection equipment at that time was not a sophisticated as it is now, and it is highly probable that errors could have occurred. Hence, it seems that most, perhaps all of all of the MPEs did happen at or under the continental crust and mostly at the edges of it.
Figure 2 represents an area where two such earthquake happened; one in December 2004 at the northwest coast of Sumatra island and generated the greatest post-earthquake tsunami in human memory, and a second one – in 2005.
Fig. 2 – The 9.0 magnitude earthquake (2004) and 8.7 magnitude earthquake (2005) off the West Coast of Sumatra island, with the epicentre located approximately 150 km and 75km north of the Java-Sumatra subduction zone and approximately 350 km and 500km from the triple junction of the Mesozoic oceanic crust, the Cenozoic oceanic crust, and the continental crust, respectively (refer to legend in Fig. 1).
Fig. 3 – Two MPREs – near the Andreanof Islands in 1957 and near the Rats Islands in 1965 – happened on a relatively thin segment of the continental crust, which is situated between the Mesozoic oceanic crust on the north (the Aleutian basin of the Bering Sea) and the Cenozoic oceanic crust on the south (part of the Pacific Ocean, south of the Aleutian subduction zone). The Rats Islands’ earthquakes were also located very close - a distance of no more than 200 km – to the triple junction of the north part of the Pacific Mesozoic oceanic crust, the Cenozoic oceanic crust, and the continental crust (refer to legend in Fig. 1).
Figure 3 shows another typical geological structure of a MPREs area. Two MPREs did occur in this area. Another nine of the seventeen MPREs also fit into the above category of earthquakes, that is, the category I classification in Table 1. The remaining six MPREs can be included in one of the following three categories:
■ Category II – earthquakes in the Himalayan-Tibetan region – 11.7 percent;
■ Category III – earthquakes that take place near the subduction of the Cenozoic oceanic crust under the continental crust – about 17.6 percent;
■ Category IV – earthquakes that are close to the triple junction of the continental crust, the Cenozoic oceanic crust, and the Plio-Quaternary oceanic ridges – only 5.8 percent.
It is hard not to concur with a common view, which has been aptly voiced by G. Beroza (2002), that, given the “limited knowledge…and [given the fact that we] lack comprehensive understanding of earthquake behavior,” maybe, even in theory, earthquakes cannot be predictable (see also the Nature web debate; http:// www. nature. com/nature/debates).
It seems, however, that the possibilities latent in the way of classifying MPREs that has been presented may provide a small but significant chance to approach a bit nearer to the prediction of earthquakes. That might seem to be the case if such a large percentage – almost 65 percent of MPREs – belonging to Category I in Table 1’s classification, did occur in areas with such specific geological similarities.
The same analysis that was presented above, but only with reference to the five most powerful earthquakes – magnitude 9.0 and higher – does not transgress the conformity that was observed.
This analysis still does not provide important clues for the prediction of earthquakes in time; however, it at least provides a reason to earmark the areas with the highest probability of the occurrence of MPREs in the foreseeable future. A list is provided below of the cities and islands that are located in the world’s most dangerous areas. Most of the areas with the highest probability of the occurrence of MPREs are located near subduction zones, with the actual presence there of the Mesozoic and Cenozoic oceanic crusts (Fig. 1).
In addition to the areas where MPREs have occurred and could happen again, a list of the planet’s most dangerous areas should include:
■ the west coast of Sumatra from the Nicobar Islands to the Mentawai Islands, down to the northern coast of Java. In the case that an earthquake in this area triggers a postearthquake tsunami, the Cocos Islands and the Christmas Islands could also be affected by the tsunami.
■ the Andreanof, Kuril, and Rats islands and the east coast of Japan. An MPREs in these areas would have a specific peculiarity. All the earthquakes in this area have occurred on a relatively narrow strip of continental crust that is situated between the oceanic crusts of two eras – the Mesozoic and the Cenozoic. Some aspects of the 1938 quake at the Banda Sea suggest that it can be placed in that category of earthquakes.
■ in addition, the Aleutian, Komandorskiye, and Kuril islands; the Hokkaido, Honshui, Izu, Bonin, Volcano, Marianas, and Guam islands; areas south of Java island; Bali, Lombok, Sumba, Sumbara, Savu, Rote, Alor, Flokes, and Timor islands; Manus, Mussau, New Ireland, and New Britain islands; Bougainville, Choiseul, S. Isabel, Guadalcanal, Makira, Santa Cruz, New Hebrides and Matthews islands; Vava’u, Tonga, Tongatapu, Kermadec, the Banks islands, and New Zealand’s northern island. All of these islands are located in those specific dangerous areas. The island of Samoa and the Solomon Islands could be affected by the accompanying tsunami in such a case.
■ it is especially necessary to note that the overpopulated island of Honshu, the location of the cities of Tokyo, Nagoya, Osaka, Kyoto, Kobek, Moriaka, and Sendai, and the island of Java, where Indonesia’s capital Jakarta is located, are subject to the greatest danger. All of them are extremely close to the high danger area that would possibly be affected by one of the predicted MPREs.
■ the South Sandwich Islands near Antarctica. They are also located in the high risk area, and, if a major earthquake happened in this area, South Georgia Island could also be affected by a major tsunami.
■ the north end of Masirah Island. A triple junction of the continental crust with the Mesozoic and the Cenozoic oceanic crust occurs at this location. The South Iranian subduction zone is 425 km north of this triple junction. Hence, the east coast of Saudi Arabia and the shelf of South Iran to some extent could be considered potentially very dangerous areas seismically. In this case, the south coast of Iran from the city of Sirik to the city of Chahbar could be affected by a major tsunami.
■ antigua, Nevis, Guadelupe, Martinique, St. Lucia, St. Vincent, Grenada islands, and the west coast of Mexico south of Acapulco could also be considered very dangerous areas according the method suggested above of determining the areas with the highest probabilities of the occurrence of MPREs.
Only 11.7 percent of all MPREs happened far from the coastline, in the interior of a continent. Both earthquakes of this type occurred in one area – the Himalayan-Tibetan region. The first one was in the foothills of Tibet, and the second one was right at a subduction zone in the Himalayas that was assumed to be nonactive and extinct. Hence, if the relatively small size of this region, as compared to the size of all seismically high risk regions, is taken into account, then the Himalayan-Tibetan region should also be included in the areas of highest seismic risk.
All of the areas of highest seismic risk, with the highest probability of occurrence of MPREs, have been marked on the GMOF presented (Fig. 1).
Discussion
The phenomenon of earthquakes has been analyzed in this work by drawing a correlation between the occurrence of MPREs and the distances of their epicentres from the Mesozoic and Cenozoic oceanic crusts. Such an earthquake prediction method may not be effective yet for the prediction of the time of earthquakes. This method has already achieved some positive results, however, and has been an opportunity to at least demarcate the planet's areas of highest seismic risk. It is important to note that the method presented not only marks areas, localized in zones, where MPREs have already occurred, but also highly dangerous areas where MPREs had not yet occurred. It is especially necessary to highlight the island of Honshu - which is the location of the cities Tokyo, Nagoya, Osaka, Kyoto, Kobek, Moriaka, and Sendai; the island of Java, where Indonesia's capital Jakarta is located; the east cost of Saudi Arabia, and the shelf of South Iran from the city of Sirik to the city of Chahbar; and the west coast of Mexico south of Acapulco. These areas are subject to the greatest danger because they are extremely close to the high risk areas that could possibly be affected by one of the predicted MPREs.*
It is important to note that the propounded earthquake prediction method reveals the relationship between the occurrence of earthquakes and the ocean floor isochrons, and perhaps establish a foundation to create a global model correlating the occurrence of earthquakes with the digital isochrons of the world’s ocean floor.
*The text above highlighted in red was written years prior to the earthquate at Honshu (Parubets, 2006).
References
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Parubets, N., 2006. The 2005 modification of GIT geological map of the ocean floor - an effective tool for the prediction of the powerful earthquakes. Insitut Cartographic de Catalunya, Institut Geologic de Catalunya, 5th European Congress Du Regional Geoscientitic Cartography, Barcelona, 2006, Vol. I, 421-423.
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