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Yan Y. Kagan Dept. Earth and Space Sciences, UCLA, Los Angeles,

Yan Y. Kagan Dept. Earth and Space Sciences, UCLA, Los Angeles, CA 90095-1567, ykagan@ucla.edu , http://eq.ess.ucla.edu/~kagan.html. Evaluation of Maximum Earthquake Size for Subduction Zones. http://moho.ess.ucla.edu/~kagan/ESC12 .ppt. Outline (EFP3: O8).

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Yan Y. Kagan Dept. Earth and Space Sciences, UCLA, Los Angeles,

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  1. Yan Y. Kagan Dept. Earth and Space Sciences, UCLA, Los Angeles, CA 90095-1567, ykagan@ucla.edu, http://eq.ess.ucla.edu/~kagan.html Evaluation of Maximum Earthquake Size for Subduction Zones http://moho.ess.ucla.edu/~kagan/ESC12.ppt

  2. Outline (EFP3: O8) Maximum earthquake size estimates for subduction zones: Historical method; Statistical method; Moment-conservation method: tectonic versus seismic moment rates – area- and site-specific.

  3. 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.

  4. A log-likelihood map for the distribution of the scalar seismic moment of earthquakes in the Flinn-Engdahl zone #19 (Japan--Kurile-Kamchatka)

  5. Review of results on spectral slope, b –Bird & Kagan, 2004 Although there are variations, none is significant with 95%-confidence. Kagan’s [1999] hypothesis of uniform b still stands.

  6. DETERMINATION OF MAXIMUM • (CORNER) MAGNITUDE: • MOMENT CONCERVATION PRINCIPLE • Seismic moment rate depends on 3 variables -- • The number of earthquakes in a region (N); • The beta-value (b-value) of G-R relation; • 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).

  7. Tectonic rate for1977-1995/6/30 period is calculated by using Kagan (JGR, 1997) parameters: W=30 km, mu=30 GPa, chi=1.0. 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.

  8. DETERMINATION OF MAXIMUM (CORNER) MAGNITUDE: SITE-SPECIFIC MOMENT 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.

  9. Calculation of Mmax for fault slip

  10. Calculation of Mmax for fault slip (cont.) For Tohoku area site-specific calculations yield Mmax estimates 8.5-9.5

  11. END Thank you

  12. EVALUATION OF MAXIMUM EARTHQUAKE SIZE FOR SUBDUCTION ZONESY. Y. KaganUCLA/ESS, Los Angeles, USA Updating our previous work (Kagan, JGR, 1997), we analyze seismicity in the Flinn-Engdahl seismic zones to infer the maximum earthquake size for major subduction zones. The maximum earthquake size is usually guessed based on the available history of earthquakes or on the subdivision of a fault into separate segments. These methods are known for their significant downward bias. There are two quantitative methods which can be applied to estimate the maximum earthquake size in any region: (1) a statistical analysis of the available earthquake record, and (2) the moment conservation principle. The latter technique allows us to study how much of the tectonic deformation rate in regions or in particular fault sites is released by earthquakes. We demonstrate that for the subduction zones the seismic or historical seismicity record is not sufficient to provide a reliable statistical measure of the maximum earthquake. However, the moment conservation principle produces consistent estimates: for all the subduction zones the maximum moment magnitude suggested by various measurements is of the order 9.0 to 9.7.

  13. Abstract continuation Moreover, the moment conservation method indicates that for all the major subduction zones the maximum earthquake size is statistically the same. Since such mega-earthquakes have occurred in several subduction zones, other zones would eventually be expected to have shocks of similar magnitude. The 2004 Sumatra and the 2011 Tohoku earthquakes occurring after 1997, demonstrated the validity of this prediction. We also consider another moment conservation method -- comparing the site-specific deformation rate and its release by earthquakes rupturing the site. Though depending on less reliable assumptions, this technique, applied to the Tohoku area, also suggests that the maximum earthquake size could be of the order M9. If the maximum earthquake size is known, the magnitude-frequency relation yields a reliable estimate of the recurrence time of mega-events.

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