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the small horizontal relative motions and dilational strainsbetween the southern part of the peninsula and adjacent ACRsto the west and southwest (Liu et al. 2007; Wang et al. 2011).The 1994 and 2011 versions of the China SCR extend asfar offshore as 700 km southeast of Hainan Island (Figures 1,2; Broadbent and Allan Cartography 1994). Bathymetric datashow that only the near-shore half of this part of the SCR is onthe continental shelf, at water depths of 0–200 m (GEBCOWorld Map Editorial Board 2006). The offshore half is beyondthe shelf edge, at depths of 200–5,000 m. As shown on themap of Broadbent and Allan Cartography (1994), the offshorehalf was interpreted as SCR crust that had been highlyextended during the Paleogene Period. However, interpretationsof more recent marine seismic-reflection profiles betweenHainan Island and southern Taiwan show thinned continentalcrust in the landward part of the surveyed area and unusuallythick oceanic crust in the seaward part (Wang et al. 2006). Theprofile interpretations imply that the crust that was consideredto be highly extended SCR crust should now be reclassified asthick oceanic crust.In summary, information published since 1994 shows thatalmost the entire eastern China continental margin underwentNeogene extension. The only potential exception is the southernpart of the Korean peninsula.South China BlockThe South China block is part of the 1994 China SCR. Theblock consists of two smaller blocks that joined during latePrecambrian time to form crust that is now tectonically stable(Qiu et al. 2000; Li et al. 2002; Zheng et al. 2006; Liu et al.2007). S-wave tomography shows that the South China blockhas thinner sedimentary cover and higher upper mantle velocitiesthan the active North China block (Feng and An 2010).Feng and An (2010) inferred that the different upper-mantlevelocities indicate thicker lithosphere in the South China blockthan in the North China block. Seismicity and geodetic strainrates are approximately as low as those of the Mongolia SCR.These comparisons allowed Liu et al. (2007) to suggest that theSouth China block is being extruded southeastward, away fromthe India-Eurasia collision zone, as a single intact entity. Shen etal. (2005) and Liu et al. (2007) used the geodetic data to computethe rate of southeastward motion as 7–8 mm/yr and 4–6mm/yr, respectively, with respect to a stable Siberia, and Wanget al. (2011) used the data to calculate a left-lateral slip rate of0.9 mm/yr between the South China and North China blocks.Active continental crust bounds the South China blockon all sides. On the north, the Qinling fold belt of Paleogeneor Neogene age separates the South China and North Chinablocks (Figure 2; Terman 1974; Ren et al. 2002). The foldbelt itself is active continental crust because it is the productof orogenic activity younger than Early Cretaceous (Table 1).The southernmost component of the fold belt is the left-lateralQinling fault system of Neogene age (Yin 2010). Thus, theQinling fault system marks the northern boundary of the SouthChina block. On the east, the South China block adjoins theactive continental crust of the eastern China continental margin.On the south, the Neogene Ailao Shan–Red River shearzone separates the South China block from the IndochinaSCR. The Ailao Shan–Red River shear zone is tens of kilometerswide, many hundreds of kilometers long, and constitutesactive continental crust, as described in a later section on theIndochina SCR. The northern edge of the shear zone marksthe south boundary of the South China block. On the west,the left-lateral Xiangshuihe-Xiaojiang fault system forms partof the block’s boundary. The fault system formed during themiddle Neogene Period and remains active today. The rest ofthe western boundary of the South China block is along theeast-dipping Sichuan Basin fault and the west-dipping thrustfaults that crop out at the eastern front of the Longmen Shanrange (Figure 2; Yin 2010; Burchfiel et al. 2008).The Longmen Shan thrust fault comprises several strandsthat crop out along different sections of the northeast-trendingLongmen Shan range front (Hubbard et al. 2010). Mostof the exposed strands of the fault crop out within the rangeand along its southeastern front. The 400-km-wide SichuanBasin is southeast of the range front and is part of the 1994China SCR (Kanter 1994). Jia et al. (2006) and Burchfiel et al.(2008) explained that the Sichuan Basin is the foreland basinproduced by orogenic movements farther west, including thoseon the Longmen Shan thrust fault. The orogenic movementscontinue, as shown by the occurrence of the M 7.9 Wenchuanearthquake in 2008 (Figure 2) and by a similar earthquake thatpaleoseismic and historical evidence dates at approximately 2ka (Liu et al. 2010).From the range front southeastward into the SichuanBasin is a belt of northeast-trending anticlines and northeaststriking,northwest-dipping reverse faults (Burchfiel et al.1995). Interpretations of well and seismic-reflection data andof geologic mapping imply that the anticlines and reverse faultsare underlain by a nearly horizontal strand of the LongmenShan fault, which propagated southeastward into the basin(Jia et al. 2006; Hubbard et al. 2010). Southeastward movementon the buried fault strand buckled the overlying stratato form the anticlines and reverse faults (Burchfiel et al. 1995,2008). Elsewhere, similar combinations of anticlines, reversefaults, and one or more underlying thrust faults deformedsedimentary strata of foreland basins and moved the strataoutward away from growing mountain ranges, as in the southern,central, and northern Appalachian mountains, the southernCanadian Rocky Mountains, the Idaho-Montana thrustbelt, and the Ouachita mountains of Oklahoma and Arkansas(for example, Rich 1934; Boyer and Elliott 1982; Perry et al.1984; Rodgers 1970; Arbenz 1988; Hatcher et al. 1990). In theSichuan Basin, deformation of the basin deposits continuedas late as Paleogene and Neogene time (Burchfiel et al. 1995;Kirby et al. 2002; Jia et al. 2006). Thus, the northwestern partof the Sichuan Basin is a deformed orogenic foreland that hasbeen active more recently than the Early Cretaceous. This conclusionresults in the reclassification of the northwestern partof the basin as active crust (Table 1).Geologic maps and cross-sections show that several of thereverse faults dip southeastward, particularly at or near theSeismological Research Letters Volume 82, Number 6 November/December 2011 977