Search

Your search keyword '"Tadashi Yamashina"' showing total 2 results
Start Over Author "Tadashi Yamashina" Language english
2 results on '"Tadashi Yamashina"'

1. Evaluation of the 2012 Indian Ocean Coseismic Fault Model in 3-D Heterogeneous Structure based on Vertical and Horizontal GNSS Observation.

Author

Cecep Pratama, Takeo Ito, Takao Tabei, Fumiaki Kimata, Gunawan, Endra, Yusaku Ohta, Tadashi Yamashina, Nurdin, Irwandi, Sugiyanto, Didik, Muksin, Umar, Ismail, Nazli, and Meilano, Irwan

Subjects
METEOROLOGICAL observations, EARTHQUAKES, GEOLOGIC faults, SEISMIC migration, TOPOGRAPHY, BATHYMETRY
Abstract

Lack of observation network in the vicinity of oceanic intraplate earthquake lead the estimation of coseismic fault slip with high uncertainty. Satriano et al. [2] and Wei et al. [3] found NNE trending left-lateral slip as the primary features. In another hand, Yue et al. [4] and Hill et al. [5] proposed WNW trending right-lateral faults structure as the main characteristic. Here, we investigate the coseismic fault model that could explain the coseismic offset both vertical and horizontal in a 3-D heterogeneous earth structure. We constructed finite element model that include threedimensional velocity structure, topography/bathymetry, spherical-earth and subducting slab. In this study, we employed scaling slip to adjust slip amount and total seismic moment. Instead of original slip amount, we preserve seismic moment as a basis comparison. Based on vertical and horizontal observation data, WNW trending right-lateral fault could fit better than NNE trending left-lateral fault. The present study demonstrates best-fit calculation using scaling slip optimized to the horizontal or vertical observation lead the both fault model worsen the misfit of vertical or horizontal component, respectively. This result analysis indicates a trade-off between vertical and horizontal component and reflects the importance of revisiting the fault slip modeling incorporating vertical and horizontal data equally. [ABSTRACT FROM AUTHOR]

Published
2018
Full Text
View/download PDF

2. Source model of an earthquake doublet that occurred in a pull-apart basin along the Sumatran fault, Indonesia

Author

Hiroyuki Kumagai, Shinji Toda, M. Nakano, Tadashi Yamashina, Sunarjo, Hiroshi Inoue, and Ryosuke Ando

Subjects
Seismic gap, Geophysics, Geochemistry and Petrology, Interplate earthquake, Intraplate earthquake, Supershear earthquake, Active fault, Elastic-rebound theory, Seismology, Aftershock, Geology, Foreshock
Abstract

SUMMARY On 2007 March 6, an earthquake doublet occurred along the Sumatran fault, Indonesia. The epicentres were located near Padang Panjang, central Sumatra, Indonesia. The first earthquake, with a moment magnitude (M w) of 6.4, occurred at 03:49 UTC and was followed two hours later (05:49 UTC) by an earthquake of similar size (M w = 6.3). We studied the earthquake doublet by a waveform inversion analysis using data from a broadband seismograph network in Indonesia (JISNET). The focal mechanisms of the two earthquakes indicate almost identical rightlateral strike-slip faults, consistent with the geometry of the Sumatran fault. Both earthquakes nucleated below the northern end of Lake Singkarak, which is in a pull-apart basin between the Sumani and Sianok segments of the Sumatran fault system, but the earthquakes ruptured different fault segments. The first earthquake occurred along the southern Sumani segment and its rupture propagated southeastward, whereas the second one ruptured the northern Sianok segment northwestward. Along these fault segments, earthquake doublets, in which the two adjacent fault segments rupture one after the other, have occurred repeatedly. We investigated the state of stress at a segment boundary of a fault system based on the Coulomb stress changes. The stress on faults increases during interseismic periods and is released by faulting. At a segment boundary, on the other hand, the stress increases both interseismically and coseismically, and may not be released unless new fractures are created. Accordingly, ruptures may tend to initiate at a pull-apart basin. When an earthquake occurs on one of the fault segments, the stress increases coseismically around the basin. The stress changes caused by that earthquake may trigger a rupture on the other segment after a short time interval. We also examined the mechanism of the delayed rupture based on a theory of a fluidsaturated poroelastic medium and dynamic rupture simulations incorporating a rheological velocity hardening effect. These models of the delayed rupture can qualitatively explain the observations, but further studies, especially based on the rheological effect, are required for quantitative studies.

Published
2010

Catalog

Books, media, physical & digital resources
See catalog results