SE ISMOLOGY AND GEOLOGY

30 4 2008 12 SE ISMOLOGY AND GEOLOGY Vol. 30, No. 4 Dec., 2008 1) 1) 1) 2) 1) 1),, 100029 2), 100029 3D,,,,,, 215km, : P315. 2 : A : 0253-4967 (2008) 04-0996 - 08 0,, 60 70, ( 1), (Burchfiel et al., 1995;, 2006a, b; Densmore et al., 2007),, ;, (B lind Fault) (Chen et a l., 1996),, Densmore (2007),,,, 810,, 3D,, 1 111, 2008-07 - 15, 2008-11 - 17 8. 0

4 : 997 1 ( ) Fig. 1 Tectonic location ( top left corner) and p lane geometry of the Dayi Fault. 1 ; 2 ; 3 ; 4 ; 5 ; 6 ; 7 ; 8,, (, 1993),, ( 2),, NW SE,, 7 9,, 13 54, ( ) ( Yeats, 1986),, NW,, 10 20 70, 200 300m,, 2, ( ),,,,,,,,

998 30 Fig. 2 2 Measured geological section of Longfengchang2W enshangou, northeast of Dayi county. 1 ; 2 ; 3 ; 4 612m, 60 70m,, 60 70m, 112,,,,?,, ( 3) 100 200m, 215km ( 3), 2,, 355 40, 3D ( 4), ( 3), NE,,,,,,,, 15 20m, 2 5m, ( 3) SE, : 40 /SE 12 25 /SE 15 ; NW NWW, : 30 /NW 12 355 /W 9 ( 5),,,, 2,, 1975, H - 48 - ( ) H - 48 - ( ) 1 200000

4 : 999 Fig. 3 3 Plane geometry at the p iedmont hillocks at the east of Dayi county. 1 ; 2 ; 3, ; 4 ; 5 ; 6 ; 7 ; 8 ; 9 a; 10 2 211,, 3 5km,,,,,, SE, 212 215km, Densmore (2007) :,

1000 30 Fig. 4 3D 4 Topographic map measured by 3D scanner at p iedmont hillock at Longquangou. 5 ( a) ( b) ( 3) Fig. 5 a. Profile of hillockπs front range at the east of outlet of Longquangou; b. Profile of hillockπs back range at Longhuangyan ( see Fig. 3 for actual location). 1, ; 2 ; 3 ; 4 ; 5 ; 6

4 : 1001,,,,,,,, 100m,,,,, SE, :,,,, 2,,,,,,,,!,. 1992. [ J ]., 6 (1) : 25 38. CHEN J ie, NAN L ing. 1992. The study and recognition of active fold [ J ]. Inland Earthquake, 6 (1) : 25 38 ( in Chi2 nese).,,,. 2000. [M ]. :. DENG Q i2dong, FENG Xian2yue, ZHANG Pei2zhen, et al. 2000. Active Tectonics of Tian Shan [M ]. Seismological Press, Beijing( in Chinese).,, Densmore A L,. 2006a. [ J ]., 24 (2) : 1 12. L I Yong, ZHOU Rong2jun, Densmore A L, et al. 2006a. Sedimentary responses to late Cenozoic thrusting and strike2 slipp ing of Longmen Shan along eastern margin of Tibetan Plateau [ J ]. Acta Sedimentologica Sinica, 24 (2) : 1 12 ( in Chinese).,, Densmore A L,. 2006b. - [ J ]., 26 (1) : 40 52. L I Yong, ZHOU Rong2jun, Densmore A L, et al. 2006b. Geomorphic evidence for the late Cenozoic strike2slipp ing and thrusting in Longmen Mountains at the eastern margin of the Tibetan p lateau [ J ]. Quaternary Science, 26 ( 1) : 40 52 ( in Chinese).,. 1993. [M ]. :. TANG Rong2chang, HAN W ei2bin. 1993. Active Faults and Earthquake in Sichuan Province [ M ]. Seismological Press, Beijing( in Chinese).,,,. 2008. M S 810 [ J ]., 30 (3) : 597

1002 30 629. XU Xi2wei,W EN Xue2ze, YE J ian2qing, et al. 2008. mogenic structure [ J ]. The M S 810 W enchuan Earthquake surface rup tures and its seis2 Seismology and Geology, 30 (3) : 597 629 ( in Chinese).,,,. 2008. 2008 810 [ J ]., 51 (4) : 1066 1073. ZHANG Pei2Zhen, XU Xi2W ei,w EN Xue2ze, et al. 2008. Slip rates and recurrence intervals of the Longmen Shan ac2 tive fault zone, and tectonic imp lications for the mechanism of the M ay 12 W enchuan earthquake, 2008, Sichuan, China [ J ].,, Densmore A L,. Chinese Journal of Geophysics, 51 (4) : 1066 1073 ( in Chinese). 2006. [ J ]., 26 (2) : 40 51. ZHOU Rong2jun, L I Yong, Densmore A L, et al. 2006. Active tectonics of the eastern margin of the Tibet Plateau [ J ]. Journal ofm ineralogy and Petrology, 26 (2) : 40 51 ( in Chinese). Burchfiel B C, Chen Z, L iu Y, et al. 1995. Tectonics of the Longmen Shan and adjacent regions, central China [ J ]. In2 ternational Geology Review, 37 (8) : 661 735. Chen S F,W ilson C J L. 1996. betan Plateau [ J ]. Emp lacement of the Longmenshan thurst2nappe belt along the eastern margin of the Ti2 J Struct Geol, 18 (4) : 413 430. Densmore A L, L I Y, EllisM A, et al. 2005. Active tectonics and erosional unloading at the eastern margin of the Tii2 betan Plateau [ J ]. Journal ofmountain Science, 2 (2) : 146 154. Densmore A L, EllisM A, L I Y, et al. 2007. Active tectonics of the Beichuan and Pengguan Faults at the eastern mar2 gin of the Tibetan Plateau [ J ]. Tectonics, 26 (4) : TC4005. L i Y, A llen P A, Densmore A L, et al. 2003. Geological evolution of the Longmen Shan foreland basin (western Si2 chuan, China) during the Late Triassic Indosinian O rogeny [ J ]. Basin Research, 15: 117 136. Yeats R S. 1986. Active faults related to folding [A ]. In: W allace R E ( ed). Active Tectonics. National Academy Press,W ashington D C.

4 : 1003 A PREL IM I NARY RESEARCH O N THE LATEST TECTO N IC D EFO RM AT IO N STYL E AND THE ACT I V I TY AGE O F THE DAY I FAUL T I N THE P I EDMO NT O F THE LO NGM EN MO UNTA I NS DONG Shao2peng 1) HAN Zhu2jun 1) YIN J in2hui 1) L I Feng 2) AN Yan2fen 1) 1) N ational Center for A ctive Fault S tudie, Institute of Geology, China Earthquake A dm inistration, B eijing 100029, China 2) China Earthquake D isaster Prevention Center, B eijing 100029, China Abstract Primary evidence of the latest tectonic deformation style and the activity age of the Dayi Fault in the Sichuan Basin are obtained by field geologicalmapp ing, and surveying with the help of 3D scanner and total station. In the region of W enshangou2longfengchang, northeast of Dayi county on the north2 western wall of the fault, the tim e of C retaceous and Neogene strataπs gentle folding was measured to be between late Neogene and early Pleistocene. And obviously its form ing time is later than the Longmen Shan Fault which controls the northwest boundary of Sichuan B asinπs M esozoic strata and show s a thrust2nappe structure. W ith the help of oil p rospecting data, fault p lane inclines to northwest, dip an2 gle changes from 10 20 in the deep to 70 at near2surface, and dep th of the upper faulted point is about 200 300m. Geological and geomorphologic evidence shows that Holocene is its latest active time. The latest tectonic deformation on the Dayi Fault is rep resented by Holocene fold. Topographi2 cally, the deformation appears as continuous p iedmont hillocks w ith traceable length of 215km, distrib2 uted en echelon in the p iedmont of the Longmen Mountains and with the p lane shape of single hillock being ellip se. Accordingly the Dayi Fault is inferred as a Holocene active blind fault on the basis of hillocksπsection shape. Key words Dayi Fault, tectonic deformation style, activity age, buried fault,, 1983, 2006 ( ),,, : 010-62009140, E - mail: dshaopeng@gmail1com