Seismites Characteristics Study Of Xujiahe Formation Of Upper Triassic In Longmenshan Fault Zone

The world shocked Ms.8.0 earthquake occured on May 12,2008 in Wenchuan area, Sichuan Province, China. Ministry of Science and Technology,Ministry of Land and Resources and China Bureau of Earthquake Made a rapid response to the earthquake 178 days after. Plans to drill 5 scientific wells on the hanging wall of co-seismic surface rupture zones, including the Yingxiu-Beichuan fault zone and Anxian-Guanxian fault zone, Longmen Shan. Hole 1(WFSD-1) is the pilot hole of hole 2(WFSD-2), located in Bajiaomiao,Hongkou,Dujiangyan, Sichuan Province. Started drill in Nov 4, 2008. Borehole site is 385 m far from Beichuan-Ying Xiu co-seismic surface rupture zones. Drill through the Yingxiu-Beichuan fault slip belt. Drill through the Pengguan complex and Xujiahe Famation from top to bottom. WFSD-3 is located at Maoerping,Jiulong, Mianzhu, Sichuan province, Started drill in Nov 4, 2008. Started drill in December 8, 2009, drilled through the Anxian-Guanxian fault slip belt. Drilled through Xujiahe Formation four, Xujiahe Formation three, Xujiahe Formation four from top to bottom, strata obviously duplicated.Seismites deposited layer has a special structure and seismite sequences.The author found a series of soft sedimentary deformation structures during the cores observation then calibrated them as seismites formed by seismic deposition. Statistics showed that seismites in borehole 1 concentrated development in depth 609.44 m ~ 648.17 m, 693.64 m ~ 717.36 m, 770.34 m ~ 812.48 m, 943.67 m ~ 1025.05 m, 1120.61 m ~ 1151.67 m. The main identification signs are liquefied sandstone veins, liquefied discharge structure layer, inner faults, irregular pulse shale liquefaction, liquefaction deformation, slightly wrinkled, microfault,situ vibration pillow beds and liquefied sand ball-and-pillow structure. Seismites in borehole 3 concentrated development in depth 256.92 ~ 293.75 m and 1267.15 ~ 1341.08 m. The main identification signs are micro wrinkles, micro-faults, stepped normal fault,earthquake cracks, deformation bedding, flame structure, liquefaction deformation, liquefaction sandstone veins, liquefied sand ball-and-pillow structure, and also found escape structure, sand volcanos, stamp structure, sandstone walls, earthquake turbidites, liquefied breccia.Seismites always has a special sedimentary sequence in the vertical direction, after studied The vertical variation characteristics of seismites in WFSD-1 and WFSD-3, summed up a more complete seismites vertical sequence. WFSD-1 has a vertical sequence as: underlying undeformed layer-shattered breccia layerliquefaction deformation layer- micro faults,microcracks layer- homogeneous layer-upper undeformed layer; WFSD-3 has a vertical sequence as: underlying undeformed layer- deformable layer- liquefied breccia layer- liquefied sandstone veins layer- liquefaction deformation layer- micro faults layer- fluidized conglomerate layer- homogeneous layer-upper undeformed layer.The period massive seismites developmented is the period that Longmenshan fault zone strongly overthrusted and rapidly uplifted,is also a intense activity period of basin controlling fault. Seismic activity during this time is losely related to the movement of Longmenshan Fault Zone. Study on the seismite of the Xujiahe formation can help us to understand the history of the ancient periodic seismic activities. According to seismites developmented in WFSD-1, 5 seismic active periods and quiet periods appear alternately. Cracks, voids, faults formed by seismics can improve reservoir property, and create conditions for storage and transport of oil and gas.