Three sub-events composing the 2011 off the Pacific coast of Tohoku Earthquake (M w 9.0) inferred from rupture imaging by back-projecting teleseismic P waves

Abstract

High-quality vertical component seismograms of teleseismic P waves recorded at 151 stations of the European seismic network have been used to image the rupture process of the 2011 Tohoku Earthquake rapidly by a two-step back-projection method. The spatio-temporal distribution of rupture fronts suggests that the earthquake ruptured northeastwards and southwestwards over a total length of more than 340 km during at least 143 s. The fact that three fault segments ruptured at regions having different lateral heterogeneities implies that the earthquake comprised three sub-events. The first sub-event ruptured northeastwards during the first 25 s, and then turned to the northwest direction. The second sub-event ruptured at a relatively high speed of 2.78∼4.70 km/s. The third sub-event ruptured with a direction variation from southwest to southeast near the latitude of 37• . In addition, considering that the first front of the second sub-event appeared at 74.6 s and was about 28 km away from the epicenter, we propose that the second sub-event might have been triggered by the localized increase in tectonic stress in the vicinity of the hypocenter that resulted from the rupture of the first sub-event.

Application of Seismic Array Processing to Earthquake Early Warning

“…5, right). Both the spatial extent and rupture history are consistent with the results of high-frequency teleseismic back projection (e.g., Ishii, 2011;Koper et al, 2011;Meng et al, 2011;Yao et al, 2011;Zhang et al, 2011). The along-strike rupture length is approximately 300 km, smaller than that of the low-frequency slip inversion (e.g., Wei et al, 2012) but consistent with the spatial extent of the source model from the high-frequency strong-motion data (Asano and Iwata, 2012).…”

Structural and thermal control of seismic activity and megathrust rupture dynamics in subduction zones: Lessons from the Mw 9.0, 2011 Tohoku earthquake

“…At smaller scales, seismic imaging studies (e.g., Yamamoto et al, 2011;Huang et al, 2011;Zhao et al, 2011;Wang et al, 2012) evidence spatial correlation between regions of high-Vp (low Vp/Vs) within the stagnant mantle wedge, and asperities of the large M7-8-class interplate deep earthquakes. Despite possible confusion between mixed mantle material properties and serpentinites (Reynard, 2013), regions of low-Vp (high Vp/Vs) within the stagnant mantle are interpreted in terms of higher degree and rates of serpentinization, possibly enhanced by fluid-saturated pore-andfracture heterogeneities in the uppermost oceanic crust (Matsubara and Obara, 2011).…”

“…Large-scale seismic tomography, refraction and reflection studies (e.g., Ito et al, 2005;Huang et al, 2011;Zhao et al, 2011;Wang et al, 2012;Nakajima et al, 2013) reveal a transition between an updip high-Vp, low Vp/Vs, low-attenuation, stagnant mantle and a downdip low-Vp, high Vp/Vs, high-attenuation flowing mantle, with a boundary that meets the plate interface at 60-80 km of depth (W2), in agreement with numerical studies (e.g., Abers et al, 2006;Wada et al, 2008;Wada and Wang, 2009) aimed at explaining the surface heat flow in the NE Japan arc (Tanaka et al, 2004).…”

Dynamic rupture simulation of the 2011 off the Pacific coast of Tohoku Earthquake: Multi-event generation within dozens of seconds

“…GPS data and low-frequency ground motions imply that a large slip region is located on the shallower side of the seismic fault Yoshida et al, 2011). On the other hand, ground motions band-passed within about 0.1-5 Hz imply that several strong motion generation areas (SMGAs) are located on the deeper side of the seismic fault (Kurahashi and Irikura, 2011;Asano and Iwata, 2012), and the high-frequency radiation area, higher than about 0.5 Hz, is also estimated, by the back-projection method, to be located on the deeper side (Ishii, 2011;Wang and Mori, 2011;Zhang et al, 2011). This indicates that the locations of seismic wave radiation areas depend on the frequency bands (Koper et al, 2011).…”