The slip distribution of the 1946 Nankai earthquake estimated from tsunami inversion using a new plate model

Abstract A new model for the shape of the Philippine Sea Plate (PSP) subducting beneath southwest Japan was constructed by combining marine seismic survey results and seismicity data. This resulted in a plate model that is generally 3–5 km shallower than previous estimates, and contains new details of plate boundary structure near the Nankai Trough axis. We estimated the slip distribution of the 1946 Nankai earthquake by inverting tsunami waveforms using the new plate boundary model, and found that the large slip off Cape Muroto and seismic moment were reduced by about 10% from the previous estimate of Tanioka and Satake (2001a) . However, we also found reason to suspect the tide gauge closest to the epicenter (at Shimotsu), and this resulted in a much more substantial reduction in the amount of slip in the eastern segment of the rupture area. We also find that our new rupture model correlates well with features of the subducting plate boundary, such as a large subducting seamount off Cape Muroto ( Kodaira et al., 2000a ). This suggests that such features have an important effect on either earthquake rupture propagation or the interseismic accumulation of elastic strain energy, or both.

[1]  M. Ando.  A fault model of the 1946 Nankaido earthquake derived from tsunami data , 1982 .

[2]  Miura,et al.  Subducted seamount imaged in the rupture zone of the 1946 nankaido earthquake , 2000, Science.

[3]  Walter H. F. Smith,et al.  Gridding with continuous curvature splines in tension , 1990 .

[4]  C. Small,et al.  The effect of seamount subduction on seismic coupling , 1997 .

[5]  P. Stoffa,et al.  Structure of the Nankai Trough Accretionary Zone from multichannel seismic reflection data , 1990 .

[6]  K. Satake,et al.  Coseismic slip distribution of the 1946 Nankai earthquake and aseismic slips caused by the earthquake , 2001 .

[7]  R. Dmowska,et al.  Local Tsunamis and Distributed Slip at the Source , 1999 .

[8]  S. Stein,et al.  A model for the motion of the Philippine Sea Plate consistent with NUVEL‐1 and geological data , 1993 .

[9]  H. Kanamori.  Tectonic implications of the 1944 Tonankai and the 1946 Nankaido earthquakes , 1972 .

[10]  C. Findlay,et al.  Subduction erosion along the Middle America convergent margin , 2000, Nature.

[11]  Phil R. Cummins,et al.  Possible splay fault slip during the 1946 Nankai earthquake , 2000 .

[12]  F. Yamazaki,et al.  Configuration of subducted Philippine Sea plate beneath the Chubu district, central Japan , 1985 .

[13]  J. Kasahara,et al.  Depth variation of the crustal structure of the subducting plate along the Nankai Trough, off Kii Channel, Japan , 1998 .

[14]  M. Ando,et al.  Source mechanisms of the 1944 Tonankai and 1946 Nankaido earthquakes: Spatial heterogeneity of rise times , 1997 .

[15]  T. Sagiya,et al.  Coseismic slip resolution along a plate boundary megathrust: The Nankai Trough, southwest Japan , 1999 .

[16]  N. Takahashi,et al.  Western Nankai Trough seismogenic zone: Results from a wide‐angle ocean bottom seismic survey , 2000 .

[17]  J. Malavieille,et al.  Deformation of accretionary wedges in response to seamount subduction: Insights from sandbox experiments , 2000 .

[18]  M. Shinohara,et al.  Micro‐seismicity around the seaward updip limit of the 1946 Nankai Earthquake dislocation area , 2001 .

[19]  A. Nakanishi,et al.  A deep strong reflector in the Nankai accretionary wedge from multichannel seismic data: Implications for underplating and interseismic shear stress release , 2002 .

[20]  Y. Kaneda,et al.  The 1946 Nankai earthquake and segmentation of the Nankai Trough , 2002 .

[21]  M. Ando.  Source mechanisms and tectonic significance of historical earthquakes along the nankai trough, Japan , 1975 .

[22]  Masaya Matsuura,et al.  Geodetic data inversion using a Bayesian information criterion for spatial distribution of fault slip , 1992 .

[23]  K. Satake.  Depth distribution of coseismic slip along the Nankai Trough, Japan, from joint inversion of geodetic and tsunami data , 1993 .

[24]  A. Nakanishi,et al.  Crustal structure across the coseismic rupture zone of the 1944 Tonankai earthquake, the central Nankai Trough seismogenic zone , 2002 .

[25]  Y. Okada.  Surface deformation due to shear and tensile faults in a half-space , 1985 .

[26]  J. Kasahara,et al.  Heterogeneous crustal structure across a seismic block boundary along the Nankai Trough , 1997 .

[27]  Larry J. Ruff,et al.  How good are our best models? Jackknifing, bootstrapping, and earthquake depth , 1989 .

[28]  H. Shiobara,et al.  Detailed subduction structure across the eastern Nankai Trough obtained from ocean bottom seismographic profiles , 1998 .

[29]  K. Satake,et al.  Detailed coseismic slip distribution of the 1944 Tonankai Earthquake estimated from tsunami waveforms , 2001 .

[30]  J. C. Savage.  A dislocation model of strain accumulation and release at a subduction zone , 1983 .

[31]  T. Yokota,et al.  11. Three-layered Distribution of Microearthquakes in Relation to Focal Mechanism Variation in the Kii Peninsula, Southwestern Honshu, Japan , 1983 .