Welcome To My Home Page: Yuji Yagi
Self introduction
Name ; Yuji Yagi
I am graduate student (doctor's program) supervised by Prof. M. Kikuchi.
I major in Earth and Planetary Physics at The University of Tokyo.
My Research Subject is Relationship between Earthquake source process and Tectonics.
Source Process of Recent Large Earthquakes
March 24, 2001 (Mw6.7) Aki-nada Earthquake (NEW)
January 26, 2001 (Mw7.6) Western India Earthquake (Revise)
November 16, 2000 - New Ireland Region, Papua New Guinea Earthquake (Mw 8.0)
October 6, 2000 (Mw6.7) Tottori, Japan, Earthquake
November 12, 1999 (Mw7.1) Turkey Earthquake
October 16, 1999 (Mw7.1) Hector Mine, California Earthquake
September 30, 1999 (Ms7.5) Oaxaca Mexico Earthquake
September 20, 1999 ( Ms7.6) Taiwan EARTHQUAKE (Revise)
August 17, 1999 ( Ms7.4) Turkey EARTHQUAKE
Recent Published Papers
(Earth, Planets and Space, 53, pp 793-803, 2001 )
Abstract. We analyzed continuous GPS data to investigate the spatial distribution of post-seismic slip associated with two large earthquakes of October 19 and December 2, 1996, in Hyuga-nada, Japan. We found that the moment release due to post-seismic events was comparable to the co-seismic moment release during the two earthquakes. The source parameters of the first post-seismic event are as follows: the moment release = 1.7 x 1019 Nm; the maximum slip = 0.06 m at about 50 km northwest from the epicenter of the first earthquake; the characteristic decay time (= final slip / initial slope) = 15 days. For the second post-seismic event, the moment release = 2.0 x 1019 Nm; the maximum slip = 0.13 m at about 15 km northwest from the epicenter of the second earthquake; the characteristic time = 100 days. In both events, the slip vectors of the downgoing Philippine Sea (PHS) Plate on the SW-striking inter-plate boundary are directed west, in accordance with the co-seismic slip. It is also shown that the sites for co-seismic slip, post-seismic slip, and aftershocks do not overlap but complementarily share the plate boundary. This suggests that individual sites are characterized by their own constitutive laws, which may control modes of moment release as well as the entire sequence.(Geophysical Research Letters)
Abstract. The rupture process of the 1999 Turkey earthquake is examined using near-field strong motion data and teleseismic body wave data jointly. The derived source parameters are as follows: (strike, dip, slip) = (268, 86, 180), nearly pure strike-slip; the seismic moment, Mo = 1.7 x e20 Nm (Mw = 7.4); the source duration = 20 sec; the fault length = 70 km; the fault width = 15 km. The rupture process is characterized by an asymmetric bilateral rupture propagation and a smooth dislocation motion. It consists of two major fault segments, a rupture propagating to the west and a second rupture propagating to the east. The maximum dislocation and the maximum dislocation velocity are 6.3 m and 2.7 m/s, respectively, both found at the former segment. The averaged dislocation is about 4 m. The extent of the coseismic rupture strongly suggests that a considerable part of the anticipated seismic gap remains unruptured.(Geophysical Research Letters)
Abstract. On October 19, 1996, a large underthrusting earthquake (Ms = 6.7), the Hyuga-nada, Japan, earthquake occurred along the southern end of Nankai trough. About two months later, a second large earthquake (Ms =6.7) occurred in the adjacent region. We study the source process of the two large earthquakes in the Hyuga-nada region and compare the coseismic rupture area with aftershock distribution. The main source parameters obtained for the first mainshock are: (strike, dip, rake) = (210, 12, 81); the seismic moment Mo = 2.7xE19 Nm (Mw = 6.9); the rupture area S = 15x25 km2, and the source duration T = 17 s. For the second main-shock, (strike, dip, rake) = (210, 12, 87); the seismic moment Mo = 1.5xE19 Nm (Mw = 6.7); the rupture area S = 18x18 km2, and the source duration T = 15 s. The coseismic rupture areas do not overlap the aftershock area, while the aftershock of the two events mutually overlap. This implies that the common aftershock region takes a role of barriers to dynamic rupture. It is also seen that the aftershock area expanded during the first one day.
Abstract. We investigate the rupture process of Hyuga-nada earthquake of April 1, 1968 (MJMA7.5). Applying a multiple-time window inversion scheme to teleseismic body wave data, we obtained a detailed spatio-temporal distribution of moment release. The main source parameters are: the seismic moment = 2.5xE20 [Nm] ; the rupture area = 64x48 [km2]; the stress drop = 3.4 [MPa] ; the focal depth = 15 [km]. The rupture consists of three major asperities: the first asperity centring about 10km south and 20km west from the hypocenter and having a maximum slip of 4.0m, the second one centring about 8km north and 5km east from the hypocenter and having a maximum slip of 3.0m, and the third one centring about 50km west from the hypocenter and having a maximum slip of 3.2m. We compare the rupture area with that of a few large events (M6.5) subsequent to the 1968 event. Then we find that the above three asperities of 1968 event coincide with the low seismicity area in the Hyuga-nada region, and do not overlap with the source area of the subsequent large events (M6.5). This rupture pattern and the seismicity suggest that an area of slab bending as well as fracture of the slab can behave as barriers during earthquake rupture. These barriers may control the maximum size of earthquake source in this region.
Poster International Union of Geodesy and Geophysics (IUGG99)
Relationship among the coseismic rupture, after-slip and aftershock area in the Hyuga-nada earthquake of October and December, 1996 (In preparation for Earth, Planets and Space)
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(1), (2)Send me e-mail to: yuji@eri.u-tokyo.ac.jp