great japan earthquake of march 11, 2011: tectonic and ...€¦ · abstract—the tectonic and...

ISSN 0001�4338, Izvestiya, Atmospheric and Oceanic Physics, 2011, Vol. 46, No. 8, pp. 978–991. © Pleiades Publishing, Ltd., 2011.Original Russian Text © I.N. Tikhonov, V.L. Lomtev, 2011, published in Geofizicheskie protsessy i biosfera, 2011, Vol. 10, No. 2, pp. 49–66.

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INTRODUCTION

An earthquake with Mw = 9.0 occurred to the eastof Honshu Island, Japan, on March 11, 2011, at 05:46 GT,or 14:46 LT (Fig. 1). Such seismic events are megae�vents, i.e., earthquakes of a planetary scale. Every cat�astrophic event is traditionally called by a propername. This event still has no final conventional name.

According to data from different sources, it wascalled the Northeastern Taiheiyou Earthquake,Tohoku�Chino Taiheiyou�oki Earthquake, or theGreat Japan Earthquake.

Let us note an interesting regularity. Such seismiccatastrophes are grouped in time (according to seismicmeasures). The last such group was observed in the1960s–1970s, including the Kamchatka earthquake ofNovember 4, 1952 (Mw = 9.0); the Chile earthquake ofMay 22, 1960 (Mw = 9.6); and the Alaska earthquakeon March 28, 1964 (Mw = 9.2).

Forty year later, a new group of earthquakes beganforming; this includes the Sumatra�Andaman earth�quake of December 26, 2004 (Mw = 9.3) and the Chileearthquake of February 27, 2010 (Mw = 8.8). TheGreat Japan Earthquake of March 11, 2011 (Mw =9.03), belongs to this group as well.

It was accompanied by a catastrophic tsunami.Waves 10–15 m (up to 20 m at certain points) in heightswept across the northeastern coast of Honshu, pene�

trating far inland (up to several kilometers) in someplaces and damaging everything in their way. Gushingover a 6�m embankment near the Fukusima�1 atomicpower plant (APP), the tsunami disabled the poweringsystem there, which had been partly destroyed by theearthquake, and initiated technogenic catastrophesunprecedented in consequence.

The islands of Japan are located within the Pacificseismic belt and are characterized by one of the highestseismic level on earth. Nevertheless, no similar earth�quakes had been observed in Japan throughout the20th century or, probably, in all of history. By a fatalconcourse of circumstances, these natural and tech�nogenic catastrophes occurred at one of the most pop�ulated Pacific coasts. This resulted in 13100 dead andinjured, 17?100 missing people, and over $300 billionin damages and material loss (according to the officialdata of the government of Japan). The disaster becamea national tragedy.

It should be also noted that the events occurred ina well�studied region with a dense network of seismicstations, a modern tsunami warning system, a highlyqualified staff, and a population of citizens very pre�pared for natural disasters [Ueda, 1978; Methods…,1984; Mogi, 1988].

A description of any damaging earthquake and itsconsequences is a complex multipronged problem. It

Great Japan Earthquake of March 11, 2011: Tectonic and Seismological Aspects

I. N. Tikhonov and V. L. LomtevInstitute of Marine Geology and Geophysics, Far Eastern Branch, Russian Academy of Sciences, Yuzhno�Sakhalinsk, Russia

Abstract—The tectonic and seismological aspects of the Great Japan Earthquake, which occurred on March 11,2011 (Mw = 9.0), at the Pacific margin of the northeastern part of Honshu Island, are discussed. The structureand seismotectonic data, seismicity, and the return period of the most powerful (M ≥ 7.6) earthquakesthroughout history and in modern times are represented. It is shown that the return period of the most pow�erful events is about 40 years, and that of megaearthquakes is 1000 years or more. A seismic gap of about800 km in length is found in the region under study, located to the south of latitude 39°N and full of after�shocks to the megaearthquake of March 11, 2011. This event is probably connected with the deep thrust alongthe Benioff zone and its structural front (Oyashio nappe at the middle Pacific continental slope). The after�shock sequences of this megaearthquake and the Sumatra�Andaman (2004) megaearthquake are compared.It is found that several of their key characteristics (the number of aftershocks, the magnitude of the mainshock, and the time of its occurrence) for 25 days are comparable for both cases with a significant difference in theenergies of aftershock processes. A probable scenario for the origination of a repeated shock with M ~ 8.0 in theJapan Trench is discussed.

Keywords: active margin, trench, focal zone, deep thrust, nappe, earthquake, megaearthquake, aftershocksequence, most powerful aftershock, scenario of aftershock development.

DOI: 10.1134/S0001433811080111

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IZVESTIYA, ATMOSPHERIC AND OCEANIC PHYSICS Vol. 46 No. 8 2011

GREAT JAPAN EARTHQUAKE OF MARCH 11, 2011 979

usually includes a review of the seismotectonics of theregion under consideration, a rank of this event in aseries of similar earthquakes that occurred earlier inthis region, a description of the seismicity anticipatingthe event, a post factum revelation of different fore�

runner effects, an estimation of the parameters of themain shock and development of the aftershock pro�cess, a mapping of macroseismic manifestations, etc.

No doubt a lot of reports, papers, books, and otherworks will be devoted to the Great Japan Earthquake

Hokkaido Island

Honshu Island

Foreshock

Main shock

H, km

8.9

6.5–7.4

5.5–6.4

4.5–5.4

0–10 km

11–20 km

21–40 km> 40

M

NA

EU

AM

PA

Okh

42°

40°

38°

36°

34°138° 140° 142° 144° 146°

Fig. 1. Positions of the epicenter of the main shock of the earthquake of March 11, 2011 (large star), its foreshock (small star),and aftershocks (circles) recorded during the first day according to the NEIC/USGS catalog. The narrow bar is the axis of thedeep trench. The inset shows the regional scheme of platform boundaries in the model [Wei and Seno, 1998]. The platforms areNorth American (NA), Eurasian (EU), Amur (AM), Pacific (PA), and Okhotsk (Okh).

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TIKHONOV, LOMTEV

of 2011. Taking this into account, the aim of this workis to provide for data on the structure and seismotec�tonics of the Pacific margin of northeastern HonshuIsland, i.e., show the cause–effect correlation betweentectonic and seismic processes; then, using data onhistorical and modern earthquakes, give some ideaabout the return of the most powerful (M ≥ 7.6) seis�mic events in this region; and, finally, estimate thescale of the event, the character of the aftershock pro�

cess development, and probable scenarios for its devel�opment based on the online seismic data received dur�ing the first 25 days after the megaevent occurred.

TECTONIC STRUCTURE OF THE REGION

The bathymetry and tectonic structure of thePacific margin of the Honshu arc (Tohoku) and theJapan Trench (900 km in length and 100 km in width)

41°

40°

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ific

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ORI 78�3

ORI 78�4

JNOC 2

438

439

441

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OC

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436

1500

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5500

5500

6000

6500

7000

6500 60

00

5500

7000 6500

3735

7000

Fig. 2. Bathymetric map of the region under study with the positions of the Japan National Oil Company (JNOC) RM�CDP pro�files and holes of the 56th cruise of the Glomar Challenger [Initial…, 1980].

5

10

10 20 30 40 50 60 70 80 90 100 11001

Oyashio nappeallochthon autochthon

WE

km

Fig. 3. Interpreted JNOC 2 depth profile [Lomtev and Patrikeev, 1983a]. AP is the accretionary prism; FA is the accretion front.The light gray color at the top shows the water layer of the Pacific Ocean, the Cenozoic sedimentary cover, the accretionary prism,and the acoustic basement of the allochthon and autochthon. The dashed lines with arrows show the reflecting areas marking thecontraction faults and assuming the shifts along them. The thick arrow shows the direction of motion of the mid�QuaternaryOyashio nappe (allochthon) and Honshu arc to the adjacent floor of the Pacific Ocean.



have been studied for more than 100 years [Ueda,1978]. Modern ideas began forming in the 1970s–1980s after the run of the drilling geobeam GlomarChallenger ship (Figs. 2, 3) and RM�CDP multichan�nel seismoprofiling (reflection method: commondepth point) [Shiki and Misava, 1980; Initial…, 1980;Matsuzawa et al., 1980]. A geological and geophysicalsurvey of the undersea outskirts of the Japanese Archi�pelago carried out by the Japan Geological Serviceheaded by Prof. E. Honsa, became an important addi�tion [Geological…, 1978, etc.]. The materials pre�sented below and ideas about the structure and seis�motectonics of the region are based on the results of ageological interpretation of the MOV and drilling datain this region [Lomtev, 1989, 2010; Lomtev and Patri�keev, 1983a, 1983b, 1985; Lomtev et al., 1997, 2004,2007].

A narrow shelf and a wide continental shoulder aredistinguished in the relief of the Pacific margin of thenortheastern part of Honshu Island (hereinafter, NEHonshu). The latter includes a slope top bench; a mid�dle slope with a broad top terrace and a step at depthsof 1–2 and 5 km; respectively; and a lower bench, orinner slope, of Japan Trench based on its accumulativefloor composed by Tsugaru turbidities (Figs. 2, 3).

The V�shaped 8�km�thick prominence of theacoustic Oyashio basement covered with the Cenozoicsea basin is clearly pronounced in the structure of themiddle slope in the JNOC 2 depth profile. This prom�inence is composed of Late Cretaceous basic sedi�ments and exposed by hole 439 and, probably, moreancient complexes [Choi, 1987]. With accounting forthe data from hole 436 on the marginal swell, byexposing Late Cretaceous rocks (opaque horizon oflayer 2 [Initial…, 1980; Patrikeev, 2009], we can con�clude that the acoustic basement of the middle slope isdoubled between the top terrace and the step (Fig. 3).

Such flat sloping allochthon wedges are callednappes or thrust nappes [Lomtev and Patrikeev, 1985].The intermittent slope reflecting areas inside theacoustic basement mask overthrust faults, which areconnected with friction at the base during the eastwardmotion of a nappe up to the superface of stratum 2(autochthon). According to drilling and RM�CDPdata, the 25�km�wide inner slope of the Japan Trenchis composed by dislocated Cainozoic rocks of anaccretionary prism of up to 4 km in thickness, oftendoubled along the western dipping thrusts (holes 434and 441 [Initial…, 1980; Lomtev and Patrikeev,1983a, 1985]).

50

100

150

200

12 34 56

78

P1

P2

C20

1I II

WE

P1

1C1 C2

Fig. 4. Combined longitudinal profile of opposing focal zones and the JNOC 2 RM�CDP profile [Lomtev and Patrikeev, 1985]:(1) the accretion front in the basement of the Pacific slope of the Honshu arc, (2) the volcanic front, (3) the aseismic front, (4)the basement of the Sea of Japan slope of the Honshu arc, (5) the Oyashio nappe front, (6) the nappe root and the position of thethermal minimum, (7) the superface of the movable autochthon (stratum 2), and (8) the accretionary prism. Black dots and theirclouds are the earthquake focuses in the Benioff and Tarakanoc zones, the region of shallow (crust) seismicity under the Honshuarc, and the adjacent part of the trench of the Sea of Japan. The accretionary prism, the Japan Trench, Honshu arc with theOyashio nappe in front, and the underlying crust�mantle substratum are distinguished.

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TIKHONOV, LOMTEV

Young thrusts and fold thrusts of the autochthonare eastern dipping due to creeping strata 1–4; they fixthe tectonic mobility of the autochthon. Since theramps on the western edge are dipping in oppositedirections, the trench should be considered a contrac�tion structure of the ramp�graben type (more pre�cisely, semigraben) with accounting for its latitudeasymmetry.

A refinement of the accretionary prism to the westfrom 4 km to 100–150 m and less with accounting fordrilling data is caused by the stripping and swirling ofthe Cenozoic sea basin during the nappe motion;therefore, they are combined into the blanket “regionalnappe–accretionary prism” tectonic pair. Taking intoaccount the position of the thermal minimum, the blan�ket deposition balance, and the cross point of opposingfocal zones, the position of the Oyashio nappe root wasdetermined at a distance of 90 km to the west of its front,i.e., under the top terrace (see Fig. 4). If the westerndip of the autochthon is kept, then the root depth is10–20 km. Therefore, the significant autochthonplunge is caused by an increasing lithostatic load to theautochthon (the tectonic pair).

Dating the structures of the Pacific margin of NETokhoku and the Japan Trench is a complicated prob�lem. Thus, the age of the Japan Trench is determinedfrom Holocene to Cretaceous–Jurassic periods[Lomtev, 1989]. In addition, the discovery of relict�Neogene–early�Quaternary fans of canyons and theirvalleys on the floor of the NW Pacific [Lomtev, 2010],formed by turbidite underflow [Lomtev et al., 1997,2004; Patrikeev, 2009; Mammerickx, 1980], reliablyfixes a mid�Quaternary (about 0.5–1 million years)age of the Japan and other trenches, as determined

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from a complex of independent signs. Let us note thatthe Tsugaru canyon, starting in the Tsugaru Straitbetween Honshu and Hokkaido islands, has the Nakvevalley and a large fan after the trench to the south ofthe Tuscarora fault bench [Lomtev et al., 1997, 2004].The drift of terrigene sediments from the island arcsand the eastern margin of Asia is dated, according todrilling data, by mid�Miocene or, probably, early�Miocene in grabens [Lomtev et al., 1997, 2004]. Thus,accounting for the data [Geologicheskoe…, 1968], wecan conclude that the history of the Honshu arc goesback to the beginning of the Miocene. It obducted tothe floor of NW Pacific to about 90 km with formationof the middle (Oyashio bench) and bottom (accretion�ary prism) slopes and the Japan Trench in the mid�Pleistocene during the Pasadena revolution. Theabsence of a rift graben (or fault) of comparable widthon the Honshu arc higher than 8–9 km in the adjacentdepth of the Sea of Japan [Geological…, 1978] capa�ble of compensating for the tectonic doubling of thecrust along the Oyashio nappe points out to its alloch�tonous occurrence and, hence, tectonic mobility.

THE MOST POWERFUL PAST EARTHQUAKES IN THE EPICENTER REGION OF THE

MEGAEVENT

According to [Usami, 1979], seismic eventsoccurred before 1892 are considered historical earth�quakes in Japan. In 1893, the Gregorian calendar wasintroduced there, changing the lunar calendar ofJapan; seismographs began to be used for earthquakerecording. The works [Musya, 1942–1943, 1949] arethe main source of data on more than 6000 historicalearthquakes in Japan. For Europeans, the work

Table 1. List of earthquakes with M ≥ 7.6 in the seismically active Japanese zone for 869–2010 [Usami, 1979]

No. Date Focal time*,h–min

Coordinates of epicenterDepth, km M

ϕ°, N λ°, E

1 July 13, 869 At night 38.5 143.8 – 8.6

2 December 2, 1611 After midnight 39.0 144.5 – 8.1

3 June 9, 1646 – 37.7 141.7 – 7.6

4 April 13, 1677 10–21 40.0 144.0 – 8.1

5 May 13, 1717 – 39.4 142.4 – 7.6

6 July 20, 1835 04–15 37.9 141.9 – 7.6

7 August 5, 1897 00–10 38.3 143.3 – 7.6

8 March 2, 1933 17–31 39.1 144.7 ~20 8.3

9 November 2, 1936 20–46 38.2 142.2 50~60 7.7

10 November 5, 1938 08–43 37.1 141.7 20 7.7

11** March 11, 2011 05–46 38.3 142.4 24 8.9

Notes: * Greenwich time.** NEIC/USGS data.



[Usami, 1979] is more accessible; it was written inEnglish and includes a catalog of historical (M ≥ 5.9)and instrumentally recorded earthquakes for 599–1975.

A large number of powerful earthquakes in Japanand around the Japanese islands forces us to limit our�selves by a small area 5 × 4° in size, including the epi�center region of the earthquake under study (see Fig. 1)with the coordinates ϕ = 35.0°–40.0°N and λ =141.0°–145°E. According to the catalog [Usami,1979] and data of the Japan Meteorology Agency[JMA…, 2011], 11 events with M ≥ 7.6 were recordedin this seismically active region from 869 to March2011 (Table 1).

According to Table 1, the most powerful past earth�quake in the region of the megaearthquake of March11, 2011, was the event of 869 with M = 8.6. Usamiestimates its magnitude according to the Richter scale,which has a threshold at M ~ 8.6 and higher. The mag�nitude of the event of 869 could be higher if he uses theKanamoti scale [Kanamori, 1983]. No such eventswere observed in the next 742 years, while 10 similarearthquakes occurred during the following 400 years.The present megaearthquake has continued the cycleof seismic activity. Thus, about a 40�year return periodof the most powerful earthquakes is observed in theregion under study in the activation phase.

MODERN SEISMICITY OF THE REGION UNDER STUDY

The Pacific margin of NE Honshu relates to theactive regions due to its seismicity. A decrease in theerror (to 1–2 km) of the earthquake hypocenter detec�tion in the 1970s allowed Japanese seismologists[Hasegawa et al., 1979] to reveal here the two�layerstructure of the Benioff focal zone dipping westward todepths of 130–200 km at an angle of 30° (Fig. 4) anddifferent types of seismic dislocations in its upper(thrusts) and lower (faults) planes. In Fig. 4, theBenioff zone (its upper plane) crops out at the middleslope in the Oyashio nappe belt. Hence, this zone canbe considered a deep thrust and the nappe can be con�sidered its structure front [Lomtev and Patrikeev,1985].

In the same period, Sakhalin seismologists headedby R.Z. Tarakanov revealed the bogen structure of theKuril segment of the Benioff zone and a shallow (50–100 km) opposing focal zone dipping eastward underthe marginal swell [Gnibidenko et al., 1980; Tara�kanov et al., 1977]. Kropotkin (1978) suggested callingit the Tarakanov zone. The outcrop of this zone at thePacific coast of Honshu Island is called an aseismicfront [Yoshii, 1975]. Thrusts oriented along the zonedipping dominate in focuses at the outcrop of this zone[Hasegawa et al., 1979].

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Considering the geography and depth of the mainshock of the catastrophic earthquake of March 11,2011, and its aftershocks, as well as the structure of thePacific slope, we can conclude that this event wascaused by a deep thrust along the Benioff zone,including its structure front (Oyashio nappe). Its scaleand energy turned out to be so large that faults of theautochthon [Lomtev, 2001] and opposing Tarakanovfocal zone activated. Let us note that the seismicity ofthe outer slope of the Japan Trench and marginalswell, especially according to seismograph data, isquite high at some places, though it is studied insuffi�ciently, especially as a part of shallow earthquakes[Gnibidenko et al., 1980; Lomtev, 2010].

As follows from Fig. 4, the Benioff and Tarakanovzones intersect under the middle slope, forming arhombic seismically active structure [Lomtev andPatrikeev, 1983b, 1985]. According to the parallelo�gram rule, combined shifts of the top terrace in itsfocuses (in the form of steep and near�vertical thrusts)are capable of exciting tsunami waves by the pistongear scheme, including the last catastrophic events ofMarch 2011 (see the inset in Fig. 4).

The region of shallow (to depths of about 30 km) orcrustal seismicity under the Honshu arc is of impor�tance in Fig. 4; it is not directly connected with theopposing focal zones. Analogously with Sakhalin[Lomtev et al., 2007], it can be caused by a gravityeastward strip of the earth’s core along the aseismicuppermost lithosphere mantle (bedding strip) with abackcreep zone along the Sea of Japan continentalmargin of Honshu.

Taking into account the small depths of the Benioffzone and the length of the Honshu arc–Japan Trenchsystem, as well as its position in the reentering struc�ture angle formed by the large Mariana and Idzu�Bonin in the south and Kuril–Kamchatka in the northarc�trench systems and their deep thrusts, we can con�clude that the components of longitudinal southernand northern side contraction can play a noticeablerole in the seismotectonics of the Honshu arc andJapan Trench.

It is important to pay attention to the increasingwater consumption from underground sources and theincreasing load to allochtonous crust from numerousobjects and infrastructures, which promote anincrease in its tectonic mobility; local settlements(Honshu Island); and, apparently, an increase in thepreparation length and magnitude of shallow earth�quakes.

Finally, key elements in the structure and seicmo�tectonics of the active Pacific margin of NE Honshuare the focal rhomb, formed by opposing deep thrustsof the Benioff and Tarakanov zones; the youngOyashio nappe; and the broad top terrace (the genera�tion zone of the pistonlike tsunami) in the middle part

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Table 2. Catalog of earthquakes in the region of Japan to the east of Hokkaido and Honshu islands with M ≥ 7.6 for 1900–2010

Date Focal time, JST h–min

Coordinates of epicenterDepth, km M Source

ϕ°, N λ°, E

01.09.1923 11–58 35.1 139.5 60 7.9

[Usami, 1979]

09.03.1931 12–49 41.2 142.5 0 7.6

03.03.1933 02–31 39.1 144.7 0–20 8.3

03.11.1936 05–46 38.2 142.2 50–60 7.7

05.11.1938 17–43 37.1 141.7 20 7.7

04.03.1952 10–32 42.15 143.85 45 8.1

16.05.1968 09–49 40.7 143.6 0 8.2

[JMA…, 2011]

16.05.1968 19–39 41.4 142.9 40 7.7

17.06.1973 12–55 43.0 146.0 40 7.8

15.01.1993 20–06 42.9 144.4 103 7.6

28.12.1994 21–19 40.0 143.7 0 7.7

26.09.2003 04–50 41.7 144.2 71 8.3

Note: The moment amplitude Mw for earthquakes of 1968–2003 is given according to [Kanamori, 1983].

of the slope. In addition, there is the accretionaryprism at the inner slope and strip of strata 1–4 at theouter one (mobile autochthon [Lomtev, 2010]) in theJapan Trench. The peculiarities of the longitudinalcontraction from the Kuril–Kamchatka and Marianaarcs (deep thrust) should be also studied.

Let us consider the most powerful earthquakesobserved in 1900–2010 to the east of Hokkaido andHonshu islands (Table 2). The focal zones of theseearthquakes are shown in Fig. 5a.

As can be seen from Fig. 5a, all the most powerfulearthquakes occurred to the north of latitude 39°N,where the focal zones are dense. The event of 1897(M = 7.6) occurred in the same region; its focus is notshown in Fig. 5a, since it is out of the considered timeframe. An extensive (800 km) region of relative quies�cence was located to the south of latitude 39°N. Thelast powerful earthquakes occurred in this region in1923, 1936, and 1938. In view of this, the relative qui�escence lasted about 75. It is seen from Fig. 5b that theseismic catastrophe of March 11, 2011, took place inthis region. Thus, there were some indications that weshould prepare for a strong earthquake near HonshuIsland, but seismologists did not pay attention tothem.

Periodicities synchronizing the occurrence of pow�erful earthquakes in different seismically active regionshave been studied in [Tikhonov, 2010]. The periodicityT = 780 day has been revealed for three regions (to theeast of Honshu and Hokkaido islands, Kamchantka,and the South Kurils) for earthquakes with M ≥ 7.6.According to observation data for about 100 years,time intervals (quiescence and alarm windows) char�acterizing the periods of decreased and increased

occurrence probability of earthquakes with M ≥ 7.7have been calculated. The corresponding curve for thefirst region is shown in Fig. 6; the circle on the curvecorresponds to the occurrence time of the Great JapanEarthquake of March 11, 2011. It occurred in the endof an alarm window (December 24, 2009–March 20,2011); i.e., it obeys the general regularity observableover the last 100 years.

THE MAIN SHOCK AND DYNAMICS OF THE PROCESS DEVELOPMENT

OF AFTERSHOCKS

According to online data from the National Earth�quake Information Center of the U.S. Geological Sur�vey (NEIC/USGS), the hypocenter was located to theeast of Honshu Island at the point ϕ = 38.32°N, λ =142.37°E at a depth of h = 24.4 km (see Fig. 1). Theearthquake resulted from the crust shifts in the contactzone of the Pacific and North American (Okhotsk)platforms [Wei and Seno, 1998] (see the inset in Fig. 1).The focal mechanism according to the data is in agood agreement with that according to the data of theHarvard Scientific Center (http://www.globalsmt.org). According to these definitions, the azimuth ofthe first nodal plane course was 162°, the slope anglewas 17°, and the slide angle was 45°; for the secondnodal plane, these parameters were 28°, 78°, and 102°,respectively. Such a mechanism corresponds to thethrust�type motion in a focus if the second nodal planeis taken as working with accounting for the fact that itscourse azimuth agrees with the first�day aftershockcloud course. According to preliminary estimates



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1931

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1994

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1936

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1938

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TIKHONOV, LOMTEV

received from GPS observations, the horizontal shiftwas about 4.5 m toward the Pacific Ocean.

The initial phase of the aftershock sequence afterthe megaearthquake to the east of Honshu Island wasapparently recorded by remote seismic stations, inparticular, those belonging to the global NEIC/USGSnetwork. Instruments at JMA stations returned off�scale readings or were broken. According to theNEIC/USGS data, about 160 shocks with M = 4.6–7.1 were recorded during the first day after the megae�arthquake (22 of them had M ≥ 6.0; Fig. 1). The after�shock process developed from the north to the southtoward Tokyo. The magnitude of the most powerfulaftershock, which originated 39 min after the mainshock, was 7.1. Looking ahead, let us note that thisvalue was not exceeded for 25 days.

About 130 aftershocks with M ≥ 4.6 were recordedon the second day (seven of them had M ≥ 6.0), andonly 86 were recorded on the third day (one shock withM = 6.0). About 875 aftershocks were recorded in25 days (Fig. 7).

Most hypocenters were located at depths of 20–40 km.The aftershock epicenters covered a large area 650 kmin length and about 350 km in width from the Honshucoast to the deep trench and even behind it.

The general character of the aftershock sequencedamping is shown in Fig. 8. For comparison, there isan analogous plot for the Sumatra�Andaman earth�quake of December 12, 2004, with M = 9.3.

It can be seen from Fig. 8 that the behavior of seis�mic processes with respect to the parameter N is simi�

2

2

lar for these megaevents, except for the first day, whenthe energies, i.e., the numbers of powerful (M ≥ 6.0)aftershocks, differ significantly: 22 aftershocks for thefirst event and only 9 for the second one.

For comparison, let us consider the number ofaftershocks for the Sumatra�Andaman earthquake,which were recorded by USGS over 25 days. Itrecorded about 680 aftershocks with M ≥ 4.6, i.e., aquite comparable number. The most powerful after�shock with M = 7.5 originated 3 h 22 min after themain shock; the fault length in the focus was 1300 km[Kosobokov, 2005]. Thus, the number of aftershocks,the magnitude of the most powerful shock, and thetime of its occurrence were comparable in both casesat a significant difference in the aftershock�processenergies.

The difference in energies between the main shockand an aftershock (the strongest over 25 days) is abouttwo units of magnitude (1000�fold relative to energy)in both cases. A vital question arises: is there a proba�bility for a more powerful aftershock of the GreatJapan Earthquake than that observed 39 min after themain shock (M = 7.1)? We know the answer for theSumatra�Andaman earthquake: an aftershock withM = 8.6 occurred three months after the main shock.

There are two answers, probable and improbable,and we believe the former, according to which onemore catastrophic earthquake with M = 8.0 ± 0.5 isprobable at NE Honshu. What is the basis for thisopinion? First, the law—discovered by M. Botom[Bath, 1965]—for the difference between the magni�

0 0.2 0.4 0.6 0.8 1.0

Kamchatka

Alarm window

the South Kurils

Quiescence window

Japan

March 11, 2011

Fig. 6. Mapping of clusters of the most powerful (M ≥ 7.7) shallow earthquakes in regions of Kamchatka, the South Kurils, andthe islands of Japan (to the east of Hokkaido and Honshu) onto the summary involute of the ring (0 and 1 is the same point) cor�responding to the period T = 780 day. The earthquake catalog data [New…, 1977; JMA…, 2011; Earthquakes…, 2003–2009] for1900–2001 (the first and the third regions) and 1918–2003 (the second region). The number of clusters in the samples n = 9.



Hokkaido Island

Honshu Island

Foreshock

Main shock

M

8.9

6.5–7.4

5.5–6.4

4.5–5.4

0–10 km

11–20 km

21–40 km

> 40 km

H

NA

EU

AM

PA

Okh

42°

40°

38°

36°

34°138° 140° 142° 144° 146°

Fig. 7. Positions of the epicenter of the main shock of the earthquake of March 11, 2011, and its foreshock and aftershocksrecorded over 25 days according to the NEIC/USGS catalog. See notations in Fig. 1.

tudes of the main shock and the most powerful after�shock, which is estimated as 12 units of magnitude;second, the similarity of aftershock processes after theJapanese megaevent and the Sumatra�Andaman

earthquake (see Fig. 5 in [Rodkin and Tikhonov,2011]).

The difference in magnitudes of the main shockand the most powerful aftershock over 25 days—equal

988


TIKHONOV, LOMTEV

160

120

80

40

0

200

150

100

50

0

1 3 5 7 9 11 13 15 17 19 21 23 25t, day

(a)

(b)

1 3 5 7 9 11 13 15 17 19 21 23 25t, day

N

N

Fig. 8. Hystograms characterizing the aftershock sequence damping of (a) the Great Japan Earthquake of March 11, 2011, and(b) the Sumatra�Andaman earthquake of December 12, 2004. N is the number of aftershocks with M ≥ 4.6 per day.

to 1.9 units of magnitude—is a unique case for thepowerful Japanese earthquakes in the region understudy. Table 3 presents 14 pairs of events (the mostpowerful main shock–strong aftershock) in this regionin 1900–2010 according to JMA data. The highestvalue Mmain – Maft = 1.8 in the table corresponds to thepair of events occurring on December 21, 1946. How�ever, this estimate is somehow uncertain, becausethere were two powerful earthquakes (M = 8.0 and 8.1)at 04:19 on December 21, 1946, in the JMA catalog;an event with M = 6.3 was recorded 3 h 26 min later.

An analysis of the parameter distribution (Mmain – Maft)is not quite correct due to the small size of the sample;therefore, let us restrict ourselves by calculating themean value of this parameter for the considered seis�mically active region. It was equal to 0.90 ± 0.44.Hence, the Bot law is true for Japanese earthquakeswith something to spare (0.3 of units of magnitude).

Another important question is as follows: if theaftershock process develops according to the Sumatra�Andaman scenario, where is the most probable loca�tion of the focus with M = 8.0 ± 0.5? In our opinion,the development of the scenario relative to its location,which was observed during the most powerful Simushirearthquakes on November 15, 2006 (Mw = 8.3), and Jan�uary 13, 2007 (Mw = 8.1), is probable [Tikhonov et al.,2008].

As is seen from Figs. 1 and 3, the aftershock regionis filled irregularly for 25 days. We can distinguish herethe basic aftershock concentration adjacent to theisland and the secondary region, located to the northof latitude 37.0°N behind the deep trench, whichserves a boundary. This spatial feature of the aftershockfield was noted in [Rodkin and Tikhonov, 2011] for arecording range of 15 days.

In the 2006 Simushir earthquake, two aftershockzones were also observed: the first one near Simushir



Table 3. Pair of earthquakes (the most powerful main shock–strong aftershock) near the islands of Japan for 1900–2010 accord�ing to the JMA

Date Focal time, JST h–min

Coordinates of epicenterDepth, km M Mmain – Maft

ϕ°, N λ°, E

02.09.1922 04–16 24.5 122.2 60 7.6 0.3

15.09.1922 04–31 24.5 122.2 60 7.3

01.09.1923 11–58 35.1 139.5 60 7.9 0.6

02.09.1923 11–46 34.9 140.2 60 7.3

09.03.1931 12–49 41.2 142.5 0 7.6 1.5

10.03.1931 02–56 40.6 143.0 60 6.1

03.03.1933 02–31 39.2 144.5 10 8.1 1.3

03.03.1933 05–42 39.8 144.4 40 6.8

03.11.1936 05–46 38.2 142.2 60 7.7 0.6

27.07.1937 04–56 38.3 142.1 40 7.1

05.11.1938 17–43 37.1 141.6 20 7.7 0.4

05.11.1938 19–50 37.3 141.7 30 7.3

07.12.1944 13–35 33.7 136.2 30 8.0 0.9

13.01.1945 03–38 34.7 137.0 0 7.1

21.12.1946 04–19 33.0 135.6 30 8.1 1.8

21.12.1946 07–45 33.3 135.6 0 6.3

04.03.1952 10–22 41.8 144.1 0 8.1 1.0

04.03.1952 10–40 42.0 144.3 10 7.1

26.11.1953 02–48 34.0 141.7 60 7.4 0.8

26.11.1953 17–14 34.0 141.5 70 6.6

16.05.1968 09–48 40.7 143.6 0 8.2 0.5

16.05.1968 19–39 41.4 142.9 40 7.7

17.06.1973 12–55 43.0 146.0 40 7.8 0.7

24.06.1973 11–43 43.0 146.8 30 7.1

28.12.1994 21–19 40.4 143.7 0 7.7 1.3

29.12.1994 05–52 40.1 143.0 0 6.4

26.09.2003 04–50 41.8 144.1 42 8.0 0.9

26.09.2003 06–08 41.7 143.7 21 7.1

Mean value of the difference Mmain – Maft 0.90

Rms deviation 0.44

990


TIKHONOV, LOMTEV

Island and the second one near the Kuril Trench. Thesecond earthquake with Mw = 8.1 occurred only in thesecond zone. In this case the aftershocks of the firstearthquake clearly showed a linearly elongated regionnear the trench where the second event occurred twomonths later.

Thus, we cannot exclude the repetition of a sce�nario similar to that which developed in the MiddleKurils. A further accumulation of data on the after�shock sequence of the Great Japan Earthquake ofMarch 11, 2011, will allow us to confirm this assump�tion or reject it.

ACKNOWLEDGMENTS

The work was supported by European FP7grantNo. 262005 SEMEP.

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SPELL: 1. Mammerickx, 2. Megaearthquake, 3. Lithospheric, 4. Misawa

great japan earthquake of march 11, 2011: tectonic and ...€¦ · abstract—the tectonic and...

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