1. Kalenda P. 1), Holub K.2), Rušajová J.2) and Neumann L.3)
XXV General Assembly IUGG 2011, Melbourne, Australia, 28 June - July 10, 2011.
TRACING THE TRAVELLING OF STRESS-DEFORMATION WAVES AFTER TOHOKU EARTHQUAKE
Kalenda P. 1), Holub K.2), Rušajová J.2) and Neumann L.3)
1) Institute of Rock Structure and Mechanics, Ac. Sci. Czech Rep., V Holešovičkách 41, Praha 8, Czech Republic ) Institute of Geonics, Ac. Sci. Czech Rep., Studentská 1768, Ostrava-Poruba, Czech Republic, Fax ) Anect a.s., Praha, A.Staška 2027/79, Praha 4
ABSTRACT
The deformation waves, which were created during the strongest earthquakes, were traced on their way around the globe. These deformation waves follow the focal mechanisms and start after the mainshocks. The deformation waves after the Chile earthquake on February 27, 2010 (M=8.8) and the Mentawai earthquake (Indonesia) on October 25, 2010 (M=7.7) used the global tectonic structures with NW-SE orientations and they spread mostly to the west – northwest . On the other hand, two deformation waves were created after the Tohoku earthquake on March 11, 2011 (M=7.3, M=9). The first, a weaker deformation wave, spread to the west from Honshu and the second one travelled to the north and through the north pole to Greenland and the Atlantic Ocean. The focal mechanism, the orientation of the active structures, and the orientation of the deformation wave of the Tohoku earthquake could be the reason for the lack of the observed deformation before the mainshock, which was not comparable with the deformation anomalies before the Chile and the Mentawai earthquakes.
COMPARISON OF MAULE, CHILE (M8.8) AND TOHOKU, JAPAN (M9) EARTHQUAKES
COMPARISON OF THE CHILE M8.8 AND THE HONSHU M9 EARTHQUAKES AND STRESS-DEFORMATION WAVES
Focal mechanisms and triggering
The focal mechanisms of both earthquakes were opposite. The movement of the continental crust was to the west in the case of the Chile EQ and to the east in the case of the Tohoku EQ (see Figs 1a, c). Both earthquakes as well as their foreshocks were triggered during an opposite phase (acceleration/deceleration) of the Length Of the Day (LOD) (see Fig. 1b) (Ostřihanský 2011).
Data processing
The variations of the amplitudes of microseisms and the so called „deformation noise“(Neumann and Kalenda 2010) (see Fig. 2 and 5) were estimated within an interval of 4-5 days (sometimes up to 9 days) after several strong earthquakes occurring recently. Then temporal series obtained were used for identification of arrival times of maximum amplitudes of individual ‘knobs’, which were considered as manifestations of the stress-deformation waves. These were generated in the broad neighbourhood of earthquake foci and then were travelling around the globe, as shown in Figs 5 and 6.
Arrival time of microseisms and/or „deformation waves“
The maxima of the first microseisms ‘knobs’ departed for Europe 9 days after the Chile mainshock and 3-4 days after the Tohoku EQ (see Figs 2, 4 and 7). The second ‘knob’ of the Chile EQ departed for Europe in the same direction as the first ‘knob’ 1.5 month later and it probably triggered the volcano activity on the Island (see Fig. 4). The microseisms ‘knob’ of the Chile EQ travelled along the NW-SE structures, the same, as in the case of the Mentawai EQ (see Fig. 3). On the other hand, the main (second) microseisms ‘knob’ of the Tohoku EQ reached Europe 5 – 6 days after the mainshock and travelled across the north pole (see Fig. 6).
The interpretation of the microseisms ‘knobs’
The direct measurement of massif deformation by vertical static pendulums showed that the maximum of the deformation, i.e. deformation „noise“, is comparable with the microseisms maximum (see Fig. 2). One of the possible mechanisms of generating the microseisms seems to be the ‘deformation wave’ triggered by strong EQs, as in the case of the Samoa EQ (M=8.1), the Chile EQ (M=8.8), the Mentawai EQ (M=7.7) (see Fig. 4) and the Tohoku EQ (M=9) (see ……….. Figs 5, 6 and 7). The deformation wave prolongs the slip ……….. between the plates, blocks and/or the crust-mantle, which starts ……….. in the focus area, mainly by creep or by other aseismic ……….. deformation.
Fig. 1. Focal mechanism of the Maule, Chile (February 27, 2010, M=8.8 and the Tohoku, Japan (March 11, 2011, M=9) earthquakes (acc. to GFZ Potsdam and L. Jolivet, ISTO, Orléans, France), compared with variations of the Earth’s rotation (Length Of the Day = LOD) (acc. to L.Ostřihanský, 2011). The Maule EQ occurred during the deceleration phase of the Earth’s rotation, the Tohoku EQ occurred during the acceleration phase.
Fig. 2. Deformation wave generated by the Mentawai EQ (and high microseisms) reached Europe 9 days after the mainshock.
Fig. 5. Travelling of microseisms „knobs“ and /or stress-deformation wave around the globe.
CONCLUSION
The microseisms anomalies and/or high deformation noise were measured after most of the recently observed strong EQs. The tracing of such microseisms ‘pockets’ or ‘knobs’ showed that these anomalies were generated by the aseismic deformation between crust blocks or lithosphere plates.
Three ‘deformation waves’ were traced on their way around the globe – after the Chile, Mentawai and Tohoku EQs. Chile and Mentawai’s deformation waves were travelling along the NW-SE structures. The Tohoku EQ and its foreshock produced two deformation waves – one (smaller) travelled to the west and the second (the main deformation wave) travelled across the north pole to the Atlantic Ocean and back through the Pacific Ocean.
Fig. 6. The travelling of the main deformation wave across the north pole from Japan. The largest amplitudes were observed at the seismic stations in the Pacific, on Spitzbergen and on Greenland. Red star – mainshock on Honshu.
Fig. 3. The deformation wave of the Mentawai EQ travelled along NW-SE structures from Tonga and Indonesia in the same way as after the Chile EQ.
Acknowledgement
This work was financially sponsored by firms CoalExp Ostrava, Anect Praha, a.s. and the Research Programmes of Academy of Sciences of the Czech Republic No. OZ and No. OZ   This study was, simultaneously, carried out within the scope of the observatory activity within the European project CzechGeo/EPOS-ID LM
References
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JOLIVET L. (1995): La deformation des continents. Éditions Hermann, Paris, pp.413.
NEUMANN, L. & KALENDA, P. (2010): Static vertical pendulum – apparatus for in-situ relative stress measurement. In: Rock stress and earthquakes (F.Xie ed.),
OSTŘIHANSKÝ, L. (2011): LOD variations and earthquake. ESC Vienna, Austria.
Fig. 4. The deformation noise on pendulum P7 in Příbram (Czech Republic). The deformation wave of the Chile EQ probably triggered the volcano activity on Iceland. All of the strongest EQs, the Samoa (M8.1), the Chile (M8.8) and the Mentawai (M7.7) generated the deformation waves.
Fig. 7. The dependence of arrival time of the smaller deformation wave, travelling in the westward direction around the globe, on the longitude of the seismic station.