Ground Motion Characteristics Of The2011Mw9.0Tohoku Japan Earthquake

The source rupture process has a significant impact on the characteristics of ground motions of the2011Mw9.0Tohoku Japan Earthquake. This paper studies the near-field ground motion characteristics of this earthquake by using the three components strong motion data from K-net and KIK-net strong motion observation network of Japan. Based on source rupture characteristic, ground motion waveform is divided into two sections to study the characteristics of PGA, PGV and SA, and to study the influence of source rupture process on near-field ground motion characteristics.1、We get the whole record、the former part and the later part peak ground acceleration contour maps and the characteristic of attenuation of observed PGA with fault distance and the comparison with the Si and Midorikawa(1999) empirical attenuation relationship by calculate the whole record、the former part and the later part peak ground acceleration of the three component data of the selected722stations. Researches show that:(1) The peak ground acceleration of the whole record of this earthquake present zonal distribution that paralleled fault strike. The Horizontal PGAs are a little larger than the vertical. The PGAs of the former part are largest at the northeast and decrease centreing on this area. The characteristic of the peak ground acceleration distribution of the later part is almost the same as the whole records. The later rupture event has important significance on the distribution of peak ground acceleration of this great earthquake.(2) the PGA of the front section ground motion corresponding to the first rupture events of Mw7.7are much smaller than the whole undivided strong motion; the attenuation characteristics of PGA of the later section ground motion are basically identical to the whole undivided strong motion. In terms of the whole undivided strong motion for this Mw9.0earthquake, the PGA are smaller than the values predicted by empirical attenuation relationship; the PGA of the front section ground motion corresponding to the first rupture events of Mw7.7are smaller than the values predicted by empirical attenuation relationship.2、We get the whole record、the former part and the later part peak ground velocity contour maps and the characteristic of attenuation of observed PGV with fault distance and the comparison with the Si and Midorikawa (1999) empirical attenuation relationship by calculate the whole record、the former part and the later part peak ground velocity of the three component data of the selected722stations. Researches show that:(1) the distribution characteristic of PGV is almost same as the distribution characteristic of PGA. The later rupture event has much important significance on the distribution of peak ground velocity than the distribution of peak ground acceleration.(2)the attenuation of PGV is lower than the empirical attenuation relationship, in terms of the whole undivided strong motion for this Mw9.0earthquake, the PGV are smaller than the values predicted by empirical attenuation relationship; Compared with PGA, the deviation of the observed PGV from the Mw9.0empirical attenuation relationship is smaller.(3)The attenuation characteristic of the PGV of the former part is almost the same as the later part. The PGV of the later part are considerably larger than the PGV of the former part when rupture distance is the same. The PGV of the front section ground motion are smaller than the values predicted by Mw7.7empirical attenuation relationship when rupture distance is less than100km, the observed PGV are smaller than the values predicted by Mw7.7empirical attenuation relationship when rupture distance is larger than100km. The PGV of the later section ground motion are smaller than the values predicted by Mw7.7empirical attenuation relationship.3、We get the SA contour maps by calculate the whole record、the former part and the later part SA of the E-W component data of the selected722stations when T=0.2s、0.5s、0.8s、1s、2s、3s、and we compare the characteristic of attenuation of observed SA with fault distance with the empirical attenuation relationship when T=0.2s、1.0s、3.0s、5.0s. Researches show that:(1) SA of the whole record of this earthquake present zonal distribution that paralleled fault strike, this regularity fade away with the increased T. The SA of the former part are larger at the northeast and attenuation centreing on this area when T=0.2s,this regularity fade away with the increased T. The characteristic of SA contour of the later part is almost the same as the whole records. The characteristic of SA contour of the later part is much similar with the whole records with the increased T.(3)The observed SA of this earthquake are much less than the values predicted by Mw9.0empirical attenuation relationship, they are also less than the values predicted by Mw7.7empirical attenuation relationship.4、We calculate the70%and90%duration of the E-W component data of the selected722stations. Researches show that:(1)The70%duration distribute between20s-150s, the70%duration distribute between30s-200s.(2)The distribution of the duration is controlled by seismogenic fault, the length of70%and90%duration increase by rupture distance.(3)The duration of the north area are larger than that of the south area in the east coast of Japan nearby the rupture.The observed PGAs, PGVs and SAs are smaller than the values predicted by Mw9.0empirical attenuation relationship, they are much close to the values corresponding to sub-event of the rupture with smaller magnitude.