Yan Y. Kagan and David D. Jackson

Dept. Earth and Space Sciences, UCLA, Los Angeles,CA 90095-1567, ykagan@ucla.edu, http://eq.ess.ucla.edu/~kagan.html

Maximum Earthquake Size for Subduction Zones

http://moho.ess.ucla.edu/~kagan/SSA12.ppt

OutlineMaximum earthquake size estimates for

subduction zones:1. Historical method;2. Statistical method;3. Moment-conservation method: tectonic

versus seismic moment rates – area- and site-specific.

Flinn-Engdahl seismic regions:

• Why select them? Regions were defined before GCMT catalog started (no selection bias), and it is easier to replicate our results (programs and tables available).

• Kagan (JGR, 1997) used these regions to estimate Mmax for several tectonic categories.

A log-likelihood

map for the distribution of the scalar

seismicmoment of earthquakes

in the Flinn-

Engdahl zone #19(Japan--Kurile-

Kamchatka)

Review of results on spectral slope, – Bird & Kagan, 2004

Although there are variations, none is significant with 95%-confidence.Kagan’s [1999] hypothesis of uniform still stands.

DETERMINATION OF MAXIMUM (CORNER) MAGNITUDE:

MOMENT CONCERVATION PRINCIPLE

Seismic moment rate depends on 3 variables --1.The number of earthquakes in a region (N);2.The beta-value (b-value) of G-R relation;3.The value of maximum (corner) magnitude.

Tectonic moment rate depends on 3 variables -- 1. Width of seismogenic zone (W - 30 -- 104 km);2. Seismic efficiency coefficient (chi - 50 -- 100%);3. Value of shear modulus (mu - 30GPa -- 49GPa).

Tectonic rate for 1977-2010/12/31 period is calculated by using Bird & Kagan (BSSA, 2004) parameters: W=104 km, mu=49 GPa, chi=0.5.

Tectonic rate for 1977-1995/6/30 period is calculated by using Kagan (JGR, 1997) parameters: W=30 km, mu=30 GPa, chi=1.0.

DETERMINATION OF MAXIMUM (CORNER) MAGNITUDE: SITE-SPECIFICMOMENT CONCERVATION PRINCIPLE

1. General (area-specific) distribution of the earthquake size, for the simplicity of calculations we take it as the truncated Pareto distribution.2. Site-specific moment distribution – large earthquakes have a bigger chance to intersect a site, hence the moment distribution is different from area-specific.3. Geometric scaling of earthquake rupture. Length-width-slip are scale-invariant, proportional to the cube root of scalar moment.4. Earthquake depth distribution is different for small versus large shocks: at least for strike-slip earthquakes large events would penetrate below the seismogenic layer.5. Most of the small earthquakes do not reach the Earth surface and therefore do not contribute to the surface fault slip.

Calculation of Mmax for fault slip

Calculation of Mmax for fault slip (cont.)

For Tohoku area site-specific calculations yield Mmax estimates 8.5-9.5

END

Thank you