Possibility of M w 9.0 mainshock triggered by diffusional propagation of after-slip from M w 7.3 foreshock

Abstract

For the 2011 off the Pacific coast of Tohoku, Japan, Earthquake, we have investigated the spatio-temporal changes in seismicity from the M w 7.3 foreshock, March 9, 2011, 11:45, to the M w 9.0 mainshock, March 11, 14:46 (Japan Standard Time). We found that seismic activities slowly migrated from the source area of the foreshock, which presumably reflected the propagation of the after-slip. The mainshock rupture was initiated when the migration reached the hypocentral location of the mainshock. We also found that the migration slowed down as it expanded, where the migration distance was well fitted by a certain curve proportional to the square root of the duration, suggesting that the propagation was limited by diffusion with a diffusion coefficient of about 10 4 m 2 s −1 . This slow slip mechanism differs from nucleation-related pre-slip traditionally applied in earthquake predictions. The obtained value of the diffusion coefficient is of the same order of magnitude as that reported for the migration of a deep non-volcanic tremor. These results appear to be compatible with a conceptual model having strongly coupled patches which, although being separated by decoupled stable regions on this plate-interface, are not mechanically isolated and which became interactive when they broke.

Seismicity near the hypocenter of the 2011 off the Pacific coast of Tohoku earthquake deduced by using ocean bottom seismographic data

“…7(d)). This result supports early studies on foreshock migration based on the onshore stations (Ando and Imanishi, 2011;Kato et al, 2012). Those works had pointed out that the foreshock activity migrated toward the MS, presumably as a result of diffusional propagation of the LSF afterslip.…”

“…In this paper, we refer to the earthquakes that preceded the M-9 earthquake as foreshocks of the Tohokuoki earthquake because of their proximity to the Tohokuoki earthquake in terms of time and space. Further, from the hypocenter catalogue published by JMA, it has been pointed out that the epicenters of the foreshocks migrated toward the hypocenter of the mainshock of the Tohoku-oki earthquake (Ando and Imanishi, 2011;Kato et al, 2012).…”

Migration of earthquakes with a small stress drop in the Tanzawa Mountains, Japan

“…Studies on spatial change of seismicity include the following papers. Ando and Imanishi (2011) investigated the seismicity between the M W 7.3 earthquake on March 9, 2011 (foreshock) and the M W 9.0 Tohoku-oki earthquake on March 11, 2011. They found that hypocenters appeared to migrate toward the M W 9.0 earthquake and proposed the possibility that these earthquakes were triggered by diffusional propagation of afterslip from the M W 7.3 foreshock.…”

Superconducting Gravimeters Detect Gravity Fluctuations Induced by Mw 5.7 Earthquake Along South Pacific Rise Few Hours Before the 2011 Mw 9.0 Tohoku-Oki Earthquake

“…8), induced by the M w 5.7 earthquake rather than either pre-seismic anomalies or the oceanic noise, which also has two dominant peaks at 5 -6 and 10 -15 s (Longuet-Higgins 1950;Hinderer et al 2007). The fluctuations are neither likely response to the accelerating process nor foreshocks before the M w 9.0 earthquake (Ando and Imanishi 2011;Kato and Yoshida 2011;Kennett et al 2011;Kato et al 2012;Tajima et al 2013). Most foreshocks have magnitudes larger than M w 5.7 and they would have influenced the gravity observations and thus need to be removed from the source detection for gravity signals with frequencies of 0.10 -0.20 Hz.…”