Japan Geoscience Union Meeting 2015

Presentation information

Oral

Symbol S (Solid Earth Sciences) » S-SS Seismology

[S-SS30] Earthquake Source Processes and Physics of Earthquakes

Mon. May 25, 2015 9:00 AM - 10:45 AM A05 (APA HOTEL&RESORT TOKYO BAY MAKUHARI)

Convener:*Ryosuke Ando(Graduate School of Science, University of Tokyo), Yuko Kase(Active Fault and Earthquake Research Center, AIST, GSJ), Chair:Shiro Hirano(Graduate School of Systems and Information Engineering, University of Tsukuba), Kazuro Hirahara(Department of Geophysics, Earth and Planetary Sciences, Graduate School of Sciences, Kyoto University)

10:15 AM - 10:30 AM

[SSS30-06] Fractal fault zone geometry and scale-dependent static stress drop

*Kenshiro OTSUKI1 (1.Department of Geology, Graduate School of Science, Tohoku Univ.)

Keywords:static stress drop, scale dependence, fault zone geometry, hierarchically selfsimilar

I have shown that fault zone geometries, composed of fault segments and jog, are hierarchically selfsimilar (Fig.1a). This inhomogeneous structure breaks down the wellknown relations among fault length, averaged seismic slip and seismic moment. The distribution of seismic slip also is pinned hierarchically by jogs, showing a spectral distribution (Fig.1b). Based on the high quality data of fault traces and slip distributions from 21 surface earthquake strike-slip faults, here I show that average static stress drop ∆σ decreases as L0.

Key Point 1
If Davof a fault (L, Dmax) is πDmax/4, ∆σ = CπDmax/4L.
For a fault composed of linked n faults with (L/n, Dmax) also Dav = πDmax/4, while ∆σ = nCπDmax/4L.
[Symbol fault length:L, maximum slip:Dmax and averaged slip:Dav, static stress drop:∆σ, proportional constant:C]

Key Point 2
Slip distributions Dx on fault segments are approximated by two simple cases below.
Cases of homogeneous frictional resistance Dx = 2(1 - ν)/G × (σyxr - σyxc) × (a2 - x2)0.5.
Cases of frictional resistance with a linear gradient Dx = (1 - ν)/G × (2σyxr - σyxc(x/a)) × (a2 - x2)0.5.
[Symbol half length of fault segments:a, Poisson's ratio:ν, remote stress:σxyr, frictional resistance:σxyc]

Key Point 3
When Ls(i,j) < Ws, ∆σav(i,j) = (7πG/8)(Dav(i,j)/Ls(i,j).
When Ls(i,j) > Ws, ∆σav(i,j) = (2G/π)(Dav (i,j)/Ws.
The static stress drops averaged over the whole fault length L0 is ∆σ = (∑∆σav(i,j)Ls(i,j)/L0.
[Symbol for j-th segment of hierarchical rank i, segment length:Ls(i,j), averaged slip:Dav(i,j), static stress drop:∆σav(i,j), thickness of seismogenic crustal layer:Ws, rigidity:G]

Analytical Results
17 among 21 data are approximated to the equation below (Fig.1c).
∆σ = 79.0 L0-0.519 (units km and MPa)