The concept of the seismogenic zone remained relevant following the 2011 Japan earthquake
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Peer-reviewed literature analyzing stress inversions and fault mechanisms following the 2011 Japan earthquake explicitly utilizes and builds upon the concepts of seismogenic zones and asperities.
Japan's National Project for Earthquake Prediction has been conducted since 1965 without success. An earthquake prediction should be a short-term prediction based on observable physical phenomena or precursors. The main reason of no success is the failure to capture precursors. Most of the financial resources and manpower of the National Project have been devoted to strengthening the seismographs networks, which are not generally effective for detecting precursors since many of precursors are non-seismic. The precursor research has never been supported appropriately because the project has always been run by a group of seismologists who, in the present author's view, are mainly interested in securing funds for seismology - on pretense of prediction. After the 1995 Kobe disaster, the project decided to give up short-term prediction and this decision has been further fortified by the 2011 M9 Tohoku Mega-quake. On top of the National Project, there are other government projects, not formally but vaguely related to earthquake prediction, that consume many orders of magnitude more funds. They are also un-interested in short-term prediction. Financially, they are giants and the National Project is a dwarf. Thus, in Japan now, there is practically no support for short-term prediction research. Recently, however, substantial progress has been made in real short-term prediction by scientists of diverse disciplines. Some promising signs are also arising even from cooperation with private sectors.
Abstract We predict, with a model (earthquake stress model) that inverts the displacements documented at 163 GNSS onshore stations of the GEONET, the change of shear and normal stresses on the megathrust near the Japan Trench over the seven years before the 2011 Mw 9.0 Tohoku-Oki earthquake. We find three areas on the megathrust with greater accumulations of shear and normal stresses before the earthquake, which match the ruptured areas of the mainshock and two largest aftershocks ( M w 7.8 and 7.4) that occurred within half an hour after the mainshock. We also find that the change of normal stress on the fault before the earthquake is not uniform but increases in the up-dip portion (shallower depth) of the fault from the hypocenter and decreases in the down-dip portion. We infer that the occurrence of the giant earthquake at the shallow portion of the megathrust may be attributed to the increase of the normal stress there, which leads to an increase of fault shear strength and allows more elastic strain energy to accumulate to prepare for the next big earthquake. Based on these results we propose a new concept of the seismogenic asperity as the area of greater accumulations of shear and normal stresses. The method presented here may be useful for predicting the rupture zone of future large earthquakes.
Abstract To understand the genesis of the 25 March 2007 Noto-Hanto earthquake (Mw 6.6), we determined high-resolution 3-D seismic velocity (Vp and Vs) and Poisson's ratio (σ) images in the epicenter area using 24,698 P-wave and 22,927 S-wave arrival times from 809 earthquakes and 265 sP depth-phase data collected from seismograms of 162 earthquakes beneath the Japan Sea. The sub-oceanic events are relocated accurately by using P-, S- and sP depth-phase arrival time data jointly. Our results demonstrate that the seismic velocity (Vp and Vs) and Poisson's ratio (σ) vary markedly in the source area. In and around the main shock hypocenter, low-velocity and high-σ anomalies are revealed, which are apt for accumulation of differential strain to bring the brittle failure. We infer that the zone with pronounced low-velocity and high Poisson's ratio beneath the source area reflects fluid-related anomalies derived either from the dehydration of the subducting Pacific slab or from permeation of sea-water through deep-seated active faults or both to the main shock hypocenter, which in turn may have facilitated the rupture initiation of the main shock and its aftershock sequence by weakening the overlying seismogenic layer beneath the region. Our study reinforces the concept of fluid-driven earthquakes in the peninsular regions, elsewhere in the world.
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