Developed tectonic relief and frequency of great earthquakes caused by normal faults in the outer slope of the Japan Trench

Iwabuchi (2012) analyzed 23 topographic profiles on the outer slope of the Japan Trench derived from swath multi-beam bathymetries. According to the study, strain rates close to the axis of the Japan Trench were estimated as 7 x 10 super(-8)/yr (at the southern Japan Trench) to 11 x 10 super(-8)/yr (at the northern most of Izu-Ogasawara Trench). Iwabuchi (2012) indicated the measurements of relative heights of horsts and grabens on only two profiles because of the limits of pages of the journal. Thus, I will show all the measurements of the relative heights of horsts and grabens in this paper. In addition to this, I will infer the frequency of great tensional earthquakes in the outer slope of the Japan Trench. It is well known that 1933 Sanriku Earthquake (Mw 8.4) is the example of tensional events in the outer slope of the trench. Topographic analyses resulted in the displacement rates of whole of the outer slope of the northern and southern Japan Trench are estimated as 3.5 mm/yr and 3.6 mm/yr, respectively. On the assumption that the great earthquake equal to 1933 Sanriku earthquake in magnitude will occur in repeatedly as the characteristic earthquake, a frequency of the great earthquake is estimated about one thousand years to one thousand and several hundred years per one earthquake. No earthquakes in large scale with M>8 are known in the outer slope of the southern Japan Trench. However, the displacement rate in the outer slope of the southern Japan Trench is almost same as the northern Japan Trench. If normal-faulting earthquake equal to the magnitude of 1933 Sanriku earthquake will occur, a frequency of the earthquake is estimated as same as the northern Japan Trench. At the northern most of Izu-Ogasawara Trench, off Boso peninsula, an average displacement rate is almost two times higher than the Japan Trench. If the great earthquake which is equal to the magnitude of 1933 Sanriku earthquake will occur in the area, a frequency of the earthquake is estimated lower than one thousand year per one earthquake.