Coseismic and postseismic slip of the 2011 magnitude-9 Tohoku-Oki earthquake

Journal name:
Nature
Volume:
475,
Pages:
373–376
Date published:
DOI:
doi:10.1038/nature10227
Received
Accepted
Published online

Most large earthquakes occur along an oceanic trench, where an oceanic plate subducts beneath a continental plate. Massive earthquakes with a moment magnitude, Mw, of nine have been known to occur in only a few areas, including Chile, Alaska, Kamchatka and Sumatra. No historical records exist of a Mw = 9 earthquake along the Japan trench, where the Pacific plate subducts beneath the Okhotsk plate, with the possible exception of the ad 869 Jogan earthquake1, the magnitude of which has not been well constrained. However, the strain accumulation rate estimated there from recent geodetic observations is much higher than the average strain rate released in previous interplate earthquakes2, 3, 4, 5, 6. This finding raises the question of how such areas release the accumulated strain. A megathrust earthquake with Mw = 9.0 (hereafter referred to as the Tohoku-Oki earthquake) occurred on 11 March 2011, rupturing the plate boundary off the Pacific coast of northeastern Japan. Here we report the distributions of the coseismic slip and postseismic slip as determined from ground displacement detected using a network based on the Global Positioning System. The coseismic slip area extends approximately 400km along the Japan trench, matching the area of the pre-seismic locked zone4. The afterslip has begun to overlap the coseismic slip area and extends into the surrounding region. In particular, the afterslip area reached a depth of approximately 100km, with Mw = 8.3, on 25 March 2011. Because the Tohoku-Oki earthquake released the strain accumulated for several hundred years, the paradox of the strain budget imbalance may be partly resolved. This earthquake reminds us of the potential for Mw9 earthquakes to occur along other trench systems, even if no past evidence of such events exists. Therefore, it is imperative that strain accumulation be monitored using a space geodetic technique to assess earthquake potential.

At a glance

Figures

  1. Tectonic setting in and around the Tohoku-Oki earthquake.
    Figure 1: Tectonic setting in and around the Tohoku-Oki earthquake.

    a, Plate configurations of the Japanese islands29. The focal mechanism of the Tohoku-Oki earthquake is taken from the Global Centroid-Moment-Tensor Project15. The red arrows indicate relative motion between the two plates at a plate boundary7, 8. b, Coupling distribution before the earthquake and recent seismicity along the Japan trench. The colour shading and contours indicate the degree of interplate coupling between the subducting Pacific plate and the overriding Okhotsk plate, estimated from GPS data recorded between April 2000 and March 20014. The degree of coupling is expressed as the backslip rate30, which is a slip deficit from the relative plate velocity. The stars mark the epicentres of large (M6.8) earthquakes that have occurred since 1923. The epicentres of the mainshock, a foreshock and earthquakes with M7.4 are marked by yellow stars and labelled with their magnitudes and/or times of occurrence. The orange area is the source area of the M = 7.6 1994 earthquake20. The dashed line shows the northeastern limit of the subducted Philippine Sea plate21 (PHS). The Okhotsk plate overrides the Pacific plate north of this limit and the Philippine Sea plate overrides the Pacific plate south of this limit. The grey rectangle represents a fault patch to estimate the backslip rate.

  2. Coseismic and postseismic displacements and estimated slip.
    Figure 2: Coseismic and postseismic displacements and estimated slip.

    a, Coseismic displacements for 10–11 March 2011, relative to the Fukue site. The black arrows indicate the horizontal coseismic movements of the GPS sites. The colour shading indicates vertical displacement. The star marks the location of the earthquake epicentre. The dotted lines indicate the isodepth contours of the plate boundary at 20-km intervals28. The solid contours show the coseismic slip distribution in metres. b, Postseismic displacements for 12–25 March 2011, relative to the Fukue site. The red contours show the afterslip distribution in metres. All other markings represent the same as in a.

  3. Coseismic slip, postseismic slip and aftershocks.
    Figure 3: Coseismic slip, postseismic slip and aftershocks.

    Estimated coseismic slip (black contour, 4-m interval) and postseismic slip (red contour, 0.2-m interval) of the Tohoku-Oki earthquake for the same period as in Fig. 2. The green dashed line indicates the northeast limit of the Philippine Sea plate. The blue dashed line indicates the ruptured area of the M = 7.6 1994 earthquake20. The grey circles show the epicentres of the aftershocks of the Tohoku-Oki earthquake for 11–25 March 2011. All other markings represent the same as in Fig. 2.

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Author information

Affiliations

  1. Geospatial Information Authority of Japan, Tsukuba, Ibaraki 305-0811, Japan

    • Shinzaburo Ozawa,
    • Takuya Nishimura,
    • Hisashi Suito,
    • Tomokazu Kobayashi,
    • Mikio Tobita &
    • Tetsuro Imakiire

Contributions

S.O., T.N. and H.S. participated in the construction of the model and wrote the manuscript. M.T., T.I. and T.K. participated in the discussion of the results and reviewed the manuscript.

Competing financial interests

The authors declare no competing financial interests.

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    The file contains Supplementary Figures 1-9 with legends and Supplementary Tables 1-4.

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