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80°100°120°140°EXPLANATIONBorder of stable continentalregion (SCR) (Kanter, 1994)80°Mongolia SCR140°Border of stable continentalregion (SCR) (this paper)40°40°Epicenter in activecontinental crustSouth China SCREpicenter in stablecontinental crust20°20°0 1,000Kilometers100°120°▲▲Figure 3. Summary of the changes from the 1994 stable continental regions (SCRs) to the SCRs of this paper (see Discussion text).the upper-crustal seismogenic zone. Therefore, nearly all of theMongolia SCR retains its SCR classification, at least in theupper crust and for the purpose of reassessing the 1994 ChinaSCR to improve estimates of CEUS Mmax.Similarly, the South China block should retain its classificationas SCR crust (Figure 3). Its lithosphere is thick. Lowseismicity and strain rates led Liu et al. (2007) to the interpretationthat the block is being extruded southeastward as anintact block. I did not find any published evidence of Neogeneextensional faulting, Neogene alkaline igneous rocks, or forelanddeformation or orogeny younger than Early Cretaceouswithin the South China block. I suggest that the block becalled the South China SCR.In contrast, the North China block, eastern China continentalmargin, and Indochina SCR fail to meet the requirementsfor classification Wheeler, Figure as 3 SCR crust (Figure 3). All threeareas contain widespread Neogene extensional faulting andabundant Neogene alkaline basaltic rocks. Thus, all threeareas underwent Neogene rifting. The Korean peninsula andthe Yellow Sea contain lesser amounts of Neogene extensionalfaulting and alkaline rocks. In addition, the northern tip of theIndochina SCR overlaps the Lanping-Simao fold belt, in whichfolding and reverse faulting deformed foreland-basin strataafter Early Cretaceous time. A better classification for all fiveareas is active continental crust.In the introduction I explained that moderate to large historicalearthquakes in the 1994 China SCR provide valuableconstraints on the value of CEUS Mmax. The realization thatmost of the 1994 China SCR is active crust reduces the numberof Southeast Asian earthquakes that are available to constrainCEUS Mmax. Figure 2 shows epicenters of 43 earthquakesof magnitude 6.0 or larger on any magnitude scale (Wheeler,in preparation). Some epicenters coincide so that the figureappears to show only 39 of them. Thirty-seven of the earthquakes,or 86 percent of the 43, are now recognized as havingoccurred in ACRs, leaving only six SCR earthquakes. The 37active-crust earthquakes had estimated moment magnitudesranging up to approximately 8. Two of the six stable-crustearthquakes occurred in the eastern part of the Mongolia SCRand four were in or on the border of the South China SCR(Figure 3). Table 2 lists the six SCR earthquakes, and doublecircles identify their epicenters in Figure 2.Moderate earthquakes can provide lower bounds onestimates of Mmax, but larger earthquakes can providetighter constraints on Mmax. Specifically, the tightest constraintson CEUS Mmax are sizes of earthquakes with aboutM 6.7 and larger (for example, see Figure 3 of Petersen et al.2008). As explained earlier, many of Earth’s larger historicalearthquakes occurred in China. As explained in this paper,recently published information indicates that nearly all ofthose larger earthquakes occurred in ACR crust instead ofSCR crust. These reclassified earthquakes are lost to estimationof CEUS Mmax. Fortunately, the development of paleoseismologyin recent decades could counterbalance this loss.Paleoseismic data allow estimation of the sizes, locations, andages of moderate to large prehistoric earthquakes (Tuttle 2001;McCalpin 2009). Wheeler (2008) estimated that earthquakesof approximately M 6.5 and larger are the most likely to yieldpaleoseismic estimates of their magnitudes, locations, and ages.Therefore, paleoseismic magnitude estimates of large prehistoricSCR earthquakes may partly counterbalance the loss oflarge Chinese earthquakes. Determination of the impact ofSeismological Research Letters Volume 82, Number 6 November/December 2011 979