iz

g Kce

ijing

f Institute of Geomechanics, Chinese Academy of Geological

a r t i c l e i n f o

on mechanisms, stressnd physical propertiesrovide crucial informa-nce of physical proper-

Tectonophysics 619620 (2014) 86100

Contents lists available at ScienceDirect

Tectonop

.e l(TCDP) at Dakeng, west-central Taiwan (after the 1999 Mw 7.6 Chi-Chi earthquake), the San Andreas Fault Observatory at Depth (SAFOD)in Parkeld, California, the Nankai Trough drilling, and the Japan trench

ties and deformation mechanisms of the fault zones at depth.The 2008Wenchuan earthquake (Mw 7.9) is one of themost devas-

tating earthquakes and caused tremendous property damage andfault zone dynamics (Wu et al., 2008; Zoback et al., 2007). A numberof scientic fault-zone drilling projects have thus been initiated, suchas the Nojima fault scientic drilling program (after the 1995 Mw 7.2Kobe earthquake, Japan), the Taiwan Chelungpu fault Drilling Project

aspects, such as fault zone properties, deformatistates, mechanical and chemical roles of uids aof the crust. Studies of downhole logs and cores ption on subsurface geology aswell as direct evidefact that the fracture directions in the hanging wall and footwall are different suggests that their stress eld direc-tion is completely different, implying that the upper Pengguan complex may not be local.

2013 Elsevier B.V. All rights reserved.

1. Introduction

Understanding the physical mechanisms in seismogenic zones thatcan nucleate large earthquakes has been a major issue in studying

Results from the above drilling projects (e.g. Berckhemer et al., 1997;Boness and Zoback, 2004; Boullier, 2011; Ito and Kiguchi, 2005; Maet al., 2006; Oshiman et al., 2001; Song et al., 2007; Zoback et al.,2007) help us improve our knowledge on active fault zones in variousFast Drilling Project (J-FAST, after the 2011Mw

Corresponding author at: Institute of Geology, ChSciences, No.26, Baiwanzhuang Road, Beijing 100037, Cfax: +86 10 68994781.

E-mail address: lihaibing06@163.com (H. Li).

0040-1951/$ see front matter 2013 Elsevier B.V. All rihttp://dx.doi.org/10.1016/j.tecto.2013.08.022sponses, each of them corresponding to certain fault-rocks. The high gamma radiation, porosity and P-wave veloc-ity, as well as low resistivity and temperature anomalies indicate that the Wenchuan earthquake fault zone islocated at 585.75594.5 m-depth, with an average inclination and dip angle of N305 and 71, respectively. TheArticle history:Received 1 March 2013Received in revised form 9 August 2013Accepted 19 August 2013Available online 28 August 2013

Keywords:Wenchuan earthquake Fault Scientic Drillingproject (WFSD)YingxiuBeichuan fault zone (YBF)Physical propertiesLoggingSeismicityWFSD-1au, Lianyungang, Jiangsu 222300, ChinaSciences, Beijing 100081, China

a b s t r a c t

The Wenchuan earthquake Fault Scientic Drilling project (WFSD) started right after the 2008 Mw 7.9Wenchuan earthquake to investigate its faulting mechanism. Hole 1 (WFSD-1) reached the YingxiuBeichuanfault (YBF), and core samples were recovered from 32 to 1201.15 m-depth. Core investigation and a suite of geo-physical downhole logs (including P-wave velocity, natural gamma ray, self-potential, resistivity, density, poros-ity, temperature, magnetic susceptibility and ultrasound borehole images) were acquired inWFSD-1. Integratedstudies of cores and logs facilitate qualitative and quantitative comparison of the structures and physical propertiesof rocks. Logging data revealed that the geothermal gradient of the volcanic Pengguan complex (above 585.75 m)is 1.85 C/100 m,while that of the sedimentary Xujiahe Formation (below 585.75 m) is 2.15 C/100 m. In general,natural gamma ray, resistivity, density, porosity, P-wave velocity andmagnetic susceptibility primarily depend onthe rock lithology. Allmajor fault zones are characterized by highmagnetic susceptibility, low density and high po-rosity, with mostly low resistivity, high natural gamma ray and sound wave velocity. The high magnetic suscepti-bility values most likely result from the transformation of magnetic minerals by frictional heating due to theearthquake. The YBF exposed inWFSD-1 can be subdivided into ve different parts based on different logging re-d Institute of Geophysical and Geochemical Exploration, Chinee No.6 brigade of Jiangsu Geology & Mineral Resources Burese Academy of Geological Sciences, Langfang, Hebei 065000, ChinaState Key Laboratory of Continental Tectonics and Dynamics, Beijing 100037, Chinac China Geological Survey, No. 45, Fuwai Street, Beijing 100037, ChinaStructural and physical property characterearthquake Fault Scientic Drilling project

Haibing Li a,b,, Zhiqin Xu a,b, Yixiong Niu c, GuangshenZhiming Sun a,f, Junling Pei a,f, Zheng Gong a,b, Marie-Lua Institute of Geology, Chinese Academy of Geological Sciences, No. 26, Baiwanzhuang Road, Beb

j ourna l homepage: www9.0 Tohoku earthquake).

inese Academy of Geologicalhina. Tel.: +86 10 68990581;

ghts reserved.ation in the Wenchuanhole 1 (WFSD-1)

ong d, Yao Huang e, Huan Wang a,b, Jialiang Si a,b,Chevalier a,b, Dongliang Liu a,b

100037, China

hysics

sev ie r .com/ locate / tectoN80,000 casualties (Hui, 2008). The surface rupture extends overlengths of 270 km and 80 km along the NESW trending YingxiuBeichuan fault (hereafter YBF) and GuanxianAnxian fault (hereafterGAF) (Fig. 1a), which are high angle (Li et al., 2013; Zhang et al., 2010)and low angle thrusts in the Longmen Shan, respectively (e.g. Li et al.,2008, 2013; Zhang et al., 2010). Surface displacements are as large as

66.7 m (e.g. Fu et al., 2011; Li et al., 2008, 2009; Liu-Zeng et al., 2010;Xu et al., 2009) in the southern segment in Shenxigou and Bajiaomiaovillages (Hongkou county), and 1012 m in the northern segment inthe Beichuan area (e.g. Fu et al., 2009; Li et al., 2008, 2009; Ran et al.,2010). To explore the mechanisms and physical properties involved inlarge displacements of the ruptured fault, two holes (WFSD-1 down to1201.15 m-depth andWFSD-2 down to 2283.56 m-depth)were drilled~400 m apart, in 20082012 in the scope of theWenchuan earthquakeFault Scientic Drilling project (WFSD), at Bajiaomiao, Hongkou county(Fig. 1b), where large surface slips (~6.7 m)were observed. Continuouscoring and downhole wireline logging were completed at depths of 32to 1201 m (WFSD-1) and 50 to 2200 m (WFSD-2). Conventional logsand ultrasonic imaging (USI) were also completed in WFSD-1.

Previous studies using the above data are numerous and include var-ious aspects of mechanical, physical and chemical properties, such asstudies of the Principal Slip Zone (PSZ), thermal structure, clay mineraland permeability of the Wenchuan earthquake slip zone (e.g. Brodskyet al., 2012; Li et al., 2010, 2013; Mori et al., 2010; Pei et al., 2010; Siet al., 2010;Wang et al., 2010; Xue et al., 2013).WFSD provides a uniqueopportunity to study the cores and logs, and to characterize the detailedphysical properties of the earthquake mechanism.

In this paper, we report the results of density, porosity, P-wave ve-locities, resistivity, magnetic susceptibility, and natural gamma raymeasurements fromWFSD-1. Thesemeasurements provide basic infor-mation to assist in the characterization of lithologic units, fault zone

structure and the correlation of cores with downhole logging data,thus contributing to our understanding of the nature of faulting duringthe 2008 Wenchuan earthquake.

2. Geological setting of the Wenchuan earthquake fault zone

TheWenchuan earthquake occurred in the transition zone betweenthe eastern margin of the Tibetan Plateau and the Sichuan Basin, withintheNorthern segment of the Longmen Shan fault zone, yielding 270 and80 km-long co-seismic surface ruptures along theYBF andGAF (Fig. 1a),respectively (Fu et al., 2011; Li et al., 2008; Liu-Zeng et al., 2010; Xuet al., 2009). Five years after the Wenchuan earthquake, on April 20,2013, the Lushan earthquake (Mw6.6) occurred along the Southern seg-ment of the Longmen Shan fault zone (Fig. 1a).

The threemega-thrust faults, YBF, GAF andWenchuanMaoxian fault(hereafter WMF) form the main Longmen Shan fault zone (Fig. 1a) (Liet al., 2006), which has a long history, with the current fault tracebeing considered as the heritage of a Late Triassic fault (Burchel et al.,1995; Densmore et al., 2007; Li et al., 2006; Wang et al., 2008).

Because of the lack of historical M N 7 earthquake records prior totheWenchuan earthquake, the Longmen Shan fault zonehas potentiallyhad time to build enough strain to trigger a large earthquake such asthat of Wenchuan. Studying theWenchuan earthquake process enablesus to understand the seismicity along the Longmen Shan fault zone and

gdu

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87H. Li et al. / Tectonophysics 619620 (2014) 86100Chen

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Fig. 1. Simplied geologic and active tectonic map of the Longmen Shan and its adjacent1991) and geological structures around theWFSD drilling sites (b) (adapted from 1: 200,0rupture zone of the 2008Wenchuan earthquake.WFSD-1 andWFSD-2 are drilled along theThe U.S. Geological Survey epicenters and focal mechanisms of the 2008 Wenchuan and th(a) (adapted from 1:500,000 geologic maps, Ministry of Geology and Mineral Resources,eologic map of Guangxian, Sichuan Bureau of Geology, 1975). Red lines represent surfacexiu-Beichuan fault zone (YBF)with thenal depth of 1201.15 and 2283.56 m, respectively.13 Lushan earthquakes are shown. Gray box shows location of Fig. 1b.Mianyang

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88 H. Li et al. / Tectonophysics 619620 (2014) 86100WFSD-1WFSD-2

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T3more importantly, it provides a good opportunity to study faultmechanism.

The WFSD project aims at better understanding the earthquakemechanism as well as the physical and chemical property changes dur-ing the earthquake (Li et al., 2013; Xu et al., 2008). The project startedon November 4th 2008, just 178 days after the main earthquake oc-curred, and is planned to deploy ve drilling sites along the two mainfault traces (WFSD-1, 2, 3, 3P and 4).

The rst drilling site (WFSD-1) is located in Bajiaomiao Village ofDujiangyan County, Sichuan province, on the hanging wall of the YBFin the Neoproterozoic Pengguan complex (Fig. 1b), ~385 m west of thesurface rupture. The Pengguan complex is distributed as a lens in thecentral Longmen Shan between theWMF and the YBF, and is highlightedas one of themost impressive components of the Longmen Shan tectonicbelt. Most of the Pengguan complex is in contact with the surroundingPaleozoicTriassic rock strata, separated by faults, except along thenorthern section where it is in contact with the Sinian sedimentaryrocks, separated by a sedimentary unconformity (Fig. 1b). The lithologyof the Pengguan complex is mostly acidic and medium-acidic intrusiverocks, including granite, plagiogranite, moyite, granodiorite, tonaliteand diorite, with a small amount of basic intrusive and effusive rocks, py-roclastic rocks and green schist faciesmetamorphic rocks (Li et al., 2002;Ma et al., 1996; Sichuan Bureau of Geology, 1975). The vertical co-seismic offset near the WFSD-1 drilling site is 66.7 m, which is consid-ered the largest vertical offset along the southern segment of the fault.The Neoproterozoic Pengguan complex overlap on top of the Late

Surface rupture

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T3Triassic Xujiahe Formation along the southern segment of the fault,where the surface rupture zone spreads into the rocks of the Xujiahe For-mation near the Pengguan complex (Li et al., 2013). The Late TriassicXujiahe Formation lies mainly to the east of the YBF, and is composedof six lithologic units (Li et al., 2002; Sichuan Bureau of Geology, 1975),where themain rocks are grayish and light grayish quartz sandstone, silt-stone, dark grayish mudstone and silty mudstone and coal.

3. Drilling procedure andWFSD-1 core characteristics

3.1. Drilling procedure

TheWFSD-1 drilling site is located along the southern segment of theYBF, in Bajiaomiao village. It was rst drilled on November 4th 2008 andwas completed on July 12th 2009. The total drilling depth is 1201.15 m,with continuous drilling cores, from the surface to the very bottom, witha total length of recovered cores almost 1146 m-long. In the upper166 m of the cores, the diameter is 76 mm, then, that of the next332 m (166498 m) is 67 mm, and from 498 to 1201.15 m, the diame-ter is 46 mm. Although the drilling cores are crumbled because of a highrecovery rate (95.4%), they can still be considered as continuous. Thewhole borehole can be subdivided into 3 parts (Fig. 2a): 1)WFSD-1 seg-ment (0304.26 m), from November 4th 2008 to January 24th 2009; 2)WFSD-1-S1 segment (166.88625.80 m), from January 24th 2009 toMarch 31st 2009); and 3) WFSD-1-S2 segment (580.071201.15 m),from April 1st 2009 to July 12th 2009.

WFSD drilling site zone

Neoproterozoic (NP)(Pengguan complex)

Volcanics Normal faultThrust faultStrike and dipof bedding

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Fault

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inued).

De

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89H. Li et al. / Tectonophysics 619620 (2014) 861003.2. Structures, lithologies and fault rocks of the drilling core samples

The lithologies revealed in the drilling cores contain volcanic rocks,granite, sandstone (rich in coal material), siltstone, liqueed brecciaand other fault-related rocks (Fig. 3). The rocks above 585.75 m-depthare volcanic rocks and granite, belonging to the major Longmen Shan

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Fig. 2.WFSD-1 drilling procedure (after Li et al., 2013). (a) Simplied geologic cross-sectiontrack) from166.88 m-depth, and third hole (WFSD-1-S2 sidetrack) from580.07 m-depth; (without casing (colors represent 6 distinctmeasurements). The ~0.15 C anomaly peak pro(Li et al., 2013). (e) Close-up of (d).geological unit the Neoproterozoic Pengguan complex; the strata be-neath 585.75 m-depth belong to the Late Triassic Xujiahe Formation,mostly composed of sandstone, siltstone, mudstone, and liqueed brec-cia, with some of them characterized as fault-related rocks (Li et al.,2013). The fault zone lies between 585 and 598 m-depth, which alsocorresponds to the transition zone between the two geological units,in which both the igneous rocks from the Pengguan complex and thesedimentary rocks from the Xujiahe Formation exist, with the latter oc-cupying a larger volume.

The rock types at depths from 3 to 181.5 m aremostly grayish-greenvolcaniclastic rocks (Fig. 3), with a signicant part also recognized asvolcanic tuff; rocks at 181.5291 m-depth are dioritic porphyrite anddiorite, in which three layers of volcanic rocks are present; lithologiesat 291575.6 m-depth are volcanic rocks, volcaniclastic rocks andsome diorite; strata between the depths of 575.6 and 585.75 m consistof cataclasite, whose protolith are granite and volcanic rocks. All of theabove rock units pertain in the Pengguan complex.

The cores at depths from 585.75 to 759 m are mainly grayish sand-stone, siltstone, dark grayish mudstone, shale and coal layers, and theythen become the main composition of the YBF zone which mostly con-sists of fault gouge and fault breccia; rocks beneath 759 m-depth aregrayish sandstone, dark grayish siltstone and liqueed breccia. Com-pared to the Xujiahe Formation strata in the whole region, the strataat depths between 585.75 and 759 m revealed in the drilling cores be-long to the third group, similarly, the rocks above 759 m-depth pertainin the second group of the Xujiahe Formation, they represent the nor-mal sedimentary series.

The fault-related rocks present within the cores are primarily faultgouge, cataclasite and fault breccia (Fig. 3). No pseudotachylite wasfound in borehole 1 but there is evidence of some pseudotachylite inHongkou outcrop (Wang et al., in this issue). Even though the faultgouge developed in different rock types with different colors (gray,dark gray and black), most of them appear in dark gray and black. Thethickness of the fault gouge layers varies from millimeters to meters(Li et al., 2013). The cataclasite commonly appears to be light gray,gray and dark gray,mostly distributed in the lower part of the Pengguan

12 15viation

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eWFSD-1 drilling site (1200-m deep hole) (Li et al., 2013), second hole (WFSD-1-S1 side-orehole diameter; (c) Borehole dip angle; (d) Temperaturemeasurements in the boreholesy reects the residual heat that was produced by friction during theWenchuan earthquakecomplex (Fig. 3). At depths of 585.75 to 759 m where fault gouges andfault breccia abound, breccia with cataclastic rocks is also found.

Based on the distribution of the fault-related rocks (Fig. 3), it is clearthat many secondary faults formed along the southern part of the YBF,most of them with fault gouge layers, therefore, the YBF zone (575.7759 m) is typical of a multiple fault core structure.

4. Methodology for geophysical logs and data acquisition

During the WFSD-1 drilling, most of the logging was accomplishedby theMicro Logger II, a loggingmachinemade by the British RG Corpo-ration. Another logging machine, the JGS-1B digital logger, made by theChongqing geological equipment factory, played a somewhat lesserrole. Logging was conducted 6 times successively during the drillingprocess (Table 1). The logging parameters are divided into 13 catego-ries: Natural Gamma Radioactivity (NGR), density, focused resistivity,apparent resistivity, natural potential, P-wave velocity, neutron porosi-ty, borehole diameter, borehole deviation, temperature, well uid con-ductivity, ultrasonic imaging and magnetic susceptibility.

Natural GammaRadioactivity logging aims atmeasuring theGammaradioactivity of thewhole rock. The density logging uses 137Cs as the ra-diation source: the emitted low energy gamma hit and penetrates intothe rocks, the energy attenuates as its goes deeper into the wall rocks,and is nally absorbed by the rocks as the energy lowers. The gammaray intensity is related to the electron density in the wall rocks, whilethe electron density of the rocks approximates its volume density. Theresistivity logging method using a normal electrode system (potentialor gradient) is called apparent resistivity logging. The neutron loggingemploys 241Am9Be as the articial source to emit high energy neutronsto hit the sidewall rocks, the neutrons collide with the H atom in the

diorite, porphyriteloose surface deposits

volcanics (pyroclastics, volcanic rocks)

siltstone, shale

sandstonemostly cataclasitehost rock unidentifiedliquid brecciasoft sediments deformation

cataclasite

fault breccia

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dark-coloredfine sandstone

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Fig. 3. Lithology (original rock, left), distribution of fault rocks (middle) and prole of fault density (right) alongWFSD-1 cores, with depths being the borehole depths (after Li et al., 2013). The Neoproterozoic Pengguan complex can be seen above585.75 m-depth, while the Late Triassic Xujiahe Formation appears below 585.75 m-depth. Fault-related rocks can be seen in both the Pengguan complex and Xujiahe Formation. A large zone of the fault rocks is continuous at depths between 575.7and 759 m, corresponding to the YBF zone.

90H.Lietal./Tectonophysics

619620

(2014)86100

rocks and turn into low energy ones, then the instrument records the Hatom index. However the H atom index has simple relation with therock porosity, consequently, the neutron loggingmeasures the apparentporosity of the wall rocks.

Each of the 6 logging was conducted before casing. At depths of 489to 789 m during the fth logging, we encountered troubles because ofhighmudweight (1.6 g/cm3), yielding an absence of radioactive densityand porosity logging at 594780 m-depth, where the ultrasonic imag-ing logging also encountered problems: the magnetic logging barelyworked at 497725 m-depth, yielding a lack of data between 725 and780 m-depth.

The sampling intervals vary for different logging parameters. For themagnetic susceptibility (borehole), apparent resistivity, temperature,well deviation, well declination, well uid conductivity, natural poten-tial, natural gamma radioactivity, and P-wave velocity, the sampling in-terval is 10 cm: while it is 1 cm for the other parameters (density, welldiameter, resistivity, porosity and magnetic susceptibility in the cores).

Cores with diameters of 76, 67 and 46 mm were retrieved fromWFSD-1 (321200 m-depth) with bit sizes of 127, 108 and 89 mm, re-spectively. Casing shoes were located at depths of 32, 166.88, 498 and809.82 m, respectively (Table 1). Cores were marked with referencelines and scanned with digital cameras in slab mode and unrolled

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50 100N

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0.0001SI

Table 1Brief introduction of the six times well logging in WFSD-1.

Logging order Logging depth(m)

Logging date Consuming time(h)

Casing position(m)

Diameter variation depth(m)

Mud type Comment

1 32275 08/12/712/8 17.5 32.00 66.12 Solid free2 166400 09/1/171/18 18.5 166.88 184.67 Solid free3 400500 09/2/192/20 15.5 166.88 482.49 Low solid4 500594 09/3/133/14 13.5 498.00 Low solid Problem occurred5 489789 09/5/206/1 39.6 498.00 High density6 7801201 09/7/127/13 29.5 779.36 809.82 Solid free

91H. Li et al. / Tectonophysics 619620 (2014) 86100

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1100

1200

a b c d e f gFig. 4. Detailed well logging curves of WFSD-1 (a) Lithological column (same legend as in Fig(c) well diameter; (d) natural gamma radiation; (e) density; (f) neutron porosity; (g) P-wave vcore; (k) pole projection of fractures at different depths (down semi-sphere).600

650

700

750

800

850

900

950

N

N

315.0/65.9200.0/48.3

61.4/61.7

324.3/81.045.2/65.2

FZ970

Yingx

iu-B

eich

uan

Faul

t Zon

e

FZ590

FZ7501100

1150

1200

1000

1050

N

N

36.3/83.3

36.9/82.8

h i j k. 3); (b) distribution of fault-related rocks in the drilling core (same legend as in Fig. 3);elocity; (h) electric resistivity; (i) magnetic susceptibility; (j) crack density in the drilling

mode, then wrapped in heat-shrinkage plastic tubes. Core images werethen aligned with the reference lines and stacked in stratigraphic col-umn for structural analyses of bedding and fractures. Logging data arereported by wireline depths, whereas drilling depths are used in coredata.

5. Rock physical properties from geophysical logs

5.1. Conventional logging

Well logging identies the lithology of unknown wall rocks via pre-existing data, such as the typical response curve characteristics of thedensity and radioactivity parameters to a specic rock type. Additional-ly, a successful well logging also requires engineering data, such as thedrilling direction and thewell declination (Fig. 2). WFSD-1 is a deviatedwell with a designed drift angle and drift azimuth of 10 and N134Erespectively. Fig. 2 illustrates the real drift angles and azimuths ofWFSD-1: the minimum drift angle is 7.84, while the maximum is 15,with an average of 11. The minimum and maximum drift azimuthsare N135E, N189E, with an average of N158E. The drift angle and azi-muth at the bottom of the borehole are 13.55 and N166E, respectively.

Fig. 2d shows the temperature logging data. The bottom tempera-ture is 37.74 C and the general geothermal gradient approximates2.05 C/100 m. The geothermal gradient in the upper 800 m is1.85 C/100 m, while the gradient below 800 m is 2.15 C/100 m. Atdepths between 585 and 600 m, the temperature increases slightly(Fig. 2e).

According to geological evidence from theWFSD-1 drilling cores (Liet al., 2013, Fig. 3), the strata above 585.75 m-depth are part of theNeoproterozoic Pengguan complex, whose lithologies are primarily

granite and volcanic rocks: while the sedimentary rocks below585.75 m belong to the Late Triassic Xujiahe Formation. The Pengguancomplex lithology uncovered in WFSD-1 is a combination of terrestrial,basic to acidic volcanic rocks and volcaniclastic rocks, dened as thevolcanic rock section of the Suxiong group, Sinian System. The rocktypes above 585.75 m include tuff, volcaniclastic rocks, granite, diorite,trachyte, quartz andesite, breccia, cataclasite and fault gouge (Fig. 3).The logging parameters differ from each other for different rock types(Fig. 4). Even though themain rock type in the Pengguan complex is ba-salt, no basaltwas found in the drilling cores: The intermediate rocks areandesite and trachyte, while diorite is another intermediate rock whichhas almost the same composition as andesite: Quartz andesite and gran-ite are acidic magmatic rocks uncovered in the cores and tuff andvolcaniclastic rocks can be divided into either acidic or intermediaterocks based on their composition. The current logging data clearlydisplay the difference between basic, intermediate, acidic andvolcaniclastic rocks. The radioactivity of these rocks increases graduallyfrombasic rocks to acidic rocks (Niu et al., 2008): the basic rocks' naturalgamma index is b20 API while that of the acidic rocks is N60 API, andthe intermediate rocks share a gamma index of 2060 API. Fig. 5shows an example in which to distinguish quartz andesite from tra-chyte. It seems that the trachyte has a relatively lower gamma index,higher density, and higher apparent resistivity and porosity than quartzandesite.

The rocks from the Xujiahe Formation uncovered in WFSD-1 coresare mostly sandstone, siltstone, mudstone, shale, conglomerate, faultbreccia and fault gouge. In sedimentary rocks, the natural gammaindex generally increases and the resistivity decreases as the mud con-tent grows higher or the grains become smaller. Similarly, the neutronporosity increases with the mud content, since the mud particles are

(mm) (API) (us/ft)0

Self-potential ConductivityMagnetic

SusceptibilityBorehole Diameter Natural Gamma P-wave Velocity(mv) (Ohm.m) (us/cm) (10 SI)-4Lithology

Resistivity WFSD-1core

56tibi

92 H. Li et al. / Tectonophysics 619620 (2014) 8610090 100 110 120 30 50 70 90 60 70 80 90 100 -13536

538

540

542

544

546

548

550

552

554

556

558

560

dept

h (m

)

Dac

iteD

acite

Trac

hyte

a b c d eFig. 5. Different logging responses of quartz-andesite (dacite) and trachyte at depths of 536(d) P-wave velocity; (e) self-potential; (f) resistivity; (g) conductivity; (h) magnetic suscep

tibility peak (h) indicates the location of the fault gouge (i). Low P-wave velocity (d) and resis-120 400 600 800 8600 8700 35 45 55

f g h i

554.20 m

555.03 m

555.91 m

555.03 m

Trac

hyte

Dac

iteFa

ult g

ouge

0 m inWFSD-1. (a) Lithological column; (b) well diameter; (c) natural gamma radiation;lity; (i) drilling core samples from 554.20555.91 m-depth. The highest magnetic suscep-

tivity (f) in this fault gouge zone.

Table 2Statistics on the occurrence of the fault zones and fault-related rocks.

Order Well depth(m)

Lithology Occurrence ()(dip direction/angle)

Attribute

1 9295 Tuff 170/50 Fault zone2 169.6171 Fault gouge, breccia 177/30 Fracture zone, much water3 171178 Breccia, fault zone 220/46 Fault zone, water inrush4 197198.6 Breccia, cataclasite, fault zone 60/70, 2630/7786 Fault zone, water inrush5 233236 Fault gouge, breccia, fault zone 150/35,188/54 Fault zone, water inrush6 286.5287 Fault breccia 283/6051 Fracture zone, much water7 290290.5 Tuff 250/50 Fault zone8 318320 Fault breccia 298/52 Fracture zone9 322324.5 Andesitic volcaniclastic rocks 201/42 Fault zone10 331331.8 Andesitic volcaniclastic rocks 275/36,18/54 Fault zone11 343.4343.6 Andesitic volcaniclastic rocks 297/50 Fault zone12 359361.3 Quartz-andesitic volcaniclastic rocks 255/60 Fracture zone

s

ure z

gaug

93H. Li et al. / Tectonophysics 619620 (2014) 86100always water-rich. In the Xujiahe Formation, rocks with a gamma indexN100 API are dened asmudstone, 90100 API aremost likely siltstone,8090 API are argillaceous siltstone, and b80 API are sandstone (Fig. 4).The coal layer in the Xujiahe Formation is hard to distinguish from thewall rock by natural gamma and resistivity, yet the coal has a smallerdensity (1.31.4 g/cm3) than the common sedimentary rocks(N2.2 g/cm3). Therefore, density is the reliable parameter to differenti-ate them, where strata with a density b2.0 are considered as coal layersexcept where the hole diameter clearly increases.

Besides the qualitative analysis of the strata uctuation and the sidewell deformation, the ultrasonic image also provides a useful way toquantitatively analyze the characteristics of strata and cracks, such asthe dip direction, dip angle and depth of theparticular foliation. By gath-ering all the planar information from borehole 1, it is appropriate to sta-tistically study the regularity among them (Fig. 4k). The statistic of theoccurrence of the main fault zone and fault-related rocks is describedin Table 2.

5.2. Subsurface structure, physical properties and log units for WFSD-1

The geophysical logs can be further classied into three major units(with minor sections) on the basis of trend, characteristics and discon-tinuity in WFSD-1. Details of each unit are described below.

13 389391 Quartz-andesitic volcaniclastic rock14 426.9427.7 Fault breccia15 465469 Quartz-andesitic tuff, breccia, fract16 494494.5 Fault breccia17 585.5590 Fault gauge, breccia18 970974.5 Coal interbedded mudstone (fault5.2.1. Unit I (Pengguan complex)As shown in Fig. 4, the comprehensive logging illustration at depths

of 32585.75 m, the density, apparent resistivity and P-wave velocityabruptly change with the well diameter, while the natural gamma andmagnetic susceptibility just slightly change. The geological unit at thisdepth is the Pengguan complex. The rocks with a gamma index

Table 3Major logging parameters in WFSD-1, at depths of 321200 m.

Well depth(m)

Logging parameters Natural gamma(API)

Density(g/cm3)

32585.75Pengguan complex

Max 108.30 3.30Min 8.20 1.12Average 47.50 2.60Medium 43.06 2.60Standard deviation 15.04 0.19

585.751200Xujiahe Formation

Max 149.75 2.73Min 23.82 1.41Average 78.18 2.52Medium 64.59 2.55Standard deviation 18.34 0.12b20 API are basic rocks, 2060 API are intermediate rocks, andN60 API are acidic igneous rocks.

The main logging parameters are listed in Table 3. Based on Fig. 4d(natural gamma curve) and Fig. 6a, the gamma index of the whole sec-tion is conned between 20 and 100 API; most of them are b60 API, re-lated rocks are considered as basic rocks; the gamma index beneath350 m-depth is generally larger than that above 350 m. The mean den-sity value is 2.6 g/m3 (Table 3), while the main density values are 2.52.7 g/cm3 and slightly decrease as the gamma index increases. The me-dium interval acoustic transit time is 71.00 s/ft (Table 3), the corre-sponding velocity is 4.29 km/s, with the interval acoustic transit timeincreasing with the gamma index (Fig. 6), yet the velocity goes the op-posite way. In addition, the interval acoustic transit time above 350 m isless than that below 350 m. The apparent resistivity decreases withdepth (Fig. 4h), the high resistivity concentrates where the gammaindex is b60 API, whereas the gamma index N60 API commonly corre-sponds to a relatively low resistivity. In general, the magnetic suscepti-bility is low for the whole section; the peaks appear mainly in theintermediate and basic volcanic rocks (gamma index b60 API)(Figs. 4i and 6d). Figs. 4, 6f and Table 3 also show that the volcanicrocks have a higher porosity, with an average value of 32.55%, and theneutron porosity increases as the gamma index decreases. The well di-ameter is also considered for measurement porosity, the measured po-rosity in a wide well is higher than that of a narrow well.

308/56,186/35 Fault zone18/65,212/53 Fault zone

one 213/41 Fault zone202/59 Fault zone305/71 Main fault zone

e) 304/78 Fault zoneThe above analysis shows that the intermediate and basic igneousrocks (gamma index b60 API) have a relatively higher density, neutronporosity, P-wave velocity, apparent resistivity andmagnetic susceptibil-ity,when comparedwith the acidic volcanic rocks. The lithologies above350 m are mainly basic and intermediate rocks while the rock typesbelow 350 m are mostly acidic rocks.

Resistivity(m)

Acoustic time(s/ft)

Neutron porosity Magnetic susceptibility(104SI)

4068.84 325.14 94.53 1847.5129.10 49.00 3.00 0.00700.90 74.20 26.60 135.10700.69 71.00 31.21 74.30910.37 28.00 16.06 206.53799.60 177.60 70.20 158.7023.09 49.60 2.83 51.99269.47 76.51 19.48 82.57320.28 63.00 10.54 77.22190.98 22.51 9.22 33.67

1 1.5 2 2.5 30

20

40

60

80

100GR(API)

DEN(g/cm )-3a0 100 200 300

0

20

40

60

80

100GR(API)

ST(us/ft)b

0 1000 2000 3000 40000

20

40

60

80

100GR(API)

c0 400 800 1200 1600 2000

0

20

40

60

80

100GR(API)

MS(10 SI)-4d-10 0 10 20 30 40 50 60 70 80 900

20

40

60

80

100GR(API)

NPOR(%)e

Fig. 6. Cross plot of the major logging parameters for the Pengguan complex at depths of 32585.75 m in WFSD-1; natural gamma radiation (NGR) vs (a) density; (b) interval acoustic

94 H. Li et al. / Tectonophysics 619620 (2014) 861005.2.2. Unit II (Xujiahe Formation)Rocks at depths of 585.751200 m are sedimentary, and mostly be-

long to a continental sedimentary sequence. From the gamma indexcurve in Fig. 4b, it is clear that the lithologies above 700 m are mostlysiltstone and shale, while the strata below 700 m aremainly sandstone.The medium density for the whole section is 2.55 g/cm3, less than thatof the volcanic rocks, but approximately that of the normal sandstone's

transit time; (c) apparent resistivity; (d) magnetic susceptibility; (e) neutron porosity.density. The density increases slightly with the gamma index but de-creases to 2.0 g/cm3 at depths of 11001200 m where the well

1 1.5 2 2.5 30

40

80

120

160GR(API)

DEN(g/cm )-3a0 40 80

0

50

100

150GR(API)

b

0 200 400 600 8000

40

80

120

160GR(API)

c0 300 600

0

40

80

120

160GR(API)

d

Fig. 7. Same as in Fig. 6 for the Xujiahe Formatiodiameter remains constant and where the presence of a coal layermight explain such a low density. We do not have density data at594790 m-depth. The acoustic time curve (Fig. 4g) shows that thecycle changes drastically, with an average value of 63 s/ft, and an aver-age wave velocity of 4.84 km/s, which is slightly higher than the veloc-ity in igneous rocks. It indicates that there is no apparent relationshipwith the gamma index (Fig. 7b). The apparent resistivity is much

lower than the volcanic rock resistivity above 585.5 m (Table 3), partic-ularly where fault gouge layers are present. The apparent resistivity is

120 160 200

ST(us/ft)

900 1200 1500

MS(10 SI)-4

-10 0 10 20 30 40 50 60 70 80 9020

40

60

80

100

120

140

160GR(API)

NPOR(%)e

n at depths of 585.751200 m inWFSD-1.

barely a dozen of m. However, the average apparent resistivity is320.28 m, almost equal to the resistivity of normal sandstone. Fig. 7cshows that the apparent resistivity of intact sandstones is mostly largerthan 200 m, and that the gamma index is b80 API, whereas the rockswith a gamma index N80 API and apparent resistivity b200 m aremuddy sandstone, such as the argillaceous siltstone and detrital sand-stone. The fault zone has a gamma index b80 API and an apparent resis-tivity b200 m. The magnetic susceptibility of the whole section isgenerally low, much lower than that for the volcanic rocks. The neutronporosity decreases with the natural gamma index (Fig. 7e), as opposedto the upper igneous rocks. Because the fault zone is mainly distributedat depths of 585.5700 m, where we have no neutron porosity logging,the average porosity is higher than the real porosity.

In conclusion, the Xujiahe Formation has a higher natural gammaindex and velocity, and a lower density, porosity, resistivity and mag-netic susceptibility than the igneous rocks from the Pengguan complex.

5.2.3. Unit III (fault zones): fault zone structures and physical propertiesBased on the statistic of the fault-related rocks (Table 2) and the

density of secondary faults (Fig. 3, Li et al., 2013), the main fault zonereected in WFSD-1 drilling cores is that of the YBF (575.7759 m). At

least 10 subsidiary faults exist between these depths: FZ590, FZ608,FZ621, FZ628, FZ639, FZ646, FZ655, FZ669, FZ678 and FZ759 (Li et al.,2013), and two more secondary faults appear far away from the mainfault zone: FZ233 (232.2233.9 m) and FZ970 (970.26971.78 m).Their logging response is quite different from the Pengguan complexandXujiahe Formation. Although they developed among those two geo-logical units, they are inuenced not only by the wall rocks but also bythe texture of the fault zone.

5.2.3.1. YBF(FZ590759). Fault rocks in the YBF zone are fault breccia,cataclasite and fault gouge, which are present on both sides of thefault zone. There are also numerous fractures (Li et al., 2013; Togoet al., 2011), or fracture-damaged zones. The depths 575.7759 m inborehole 1 correspond to the YBF zone. The lithologies vary greatlydownward (Fig. 8): cataclasite zone (575.7585.75 m), black gougelayers with fault breccia (585.75595.5 m), dark fault breccia withthin gouge layers (595.5693.5 m), grayish fault breccia zone (693.5751 m) and black fault gouge layers with fault breccia (751759 m).Interestingly, the 5 fault rock units were also foundnear the ground sur-face at Hongkou village (Wang et al., in this issue). The boundary be-tween the upper cataclasite zone and the lower fault gouge and

0 30 60 90 120 150 0 50 100 150 200 -150 -100 0 200 400 600 800

Natural Gamma P-wave Velocity ResistivitySelf-potential(API) (mv) (Ohm.m)(us/ft)

Zon

e

200 400 600 800Fault rocks

0

Magnetic Susceptibility(10 SI)-4

1000

Cataclasite Zone

Black Gouge Zone

Fracture-DamagedZone

500

550

600

)

PSZ of the Wenchuan earthquake

ntial

95H. Li et al. / Tectonophysics 619620 (2014) 86100b ca

700

750

800

Fig. 8. Fault rocks (a) with natural gamma ray radiation (b), P-wave velocity (c), self-pote650

Dep

th (mWFSD-1 borehole (500800 m-depth).d e f

Fracture-DamagedZone

Black Gouge (coal seam) Zone

(d), resistivity (e) and magnetic susceptibility (f) logs from the YBF zone (FZ590759) inYing

xiu

-Bei

chua

nFa

ult

Gray Breccia Zone

Dark grayBreccia + Gouge

Zone

breccia zone is easily distinguishable, and it is also the boundary be-tween the Pengguan complex and the Xujiahe Formation, which has adip direction of 317 and a dip angle of 63.

The natural gamma radiation, P-wave velocity, natural potential andapparent resistivity are plotted in Fig. 8, but density and porosity are notavailable for this section. The resistivity is lowwhile the P-wave velocityis high for the whole fault zone. The fault gouge shows a high naturalgamma index (80120 API), a high P-wave velocity and low resistivity.On the contrary, the cataclasite shares a low natural gamma index,P-wave velocity and self-potential. From the logging data, the YBFzone seems to have 5 different units with different logging responses,and they correspond well with the lithological zones in the drillingcores as discussed above.

5.2.3.2. FZ233. The FZ233 fault core (zone) ranges from 232.2 to233.9 m-depth in volcanic rocks with signicant fracture deformation(Fig. 9). FZ233 is composed, from top to bottom, of fault breccia(~36 cm), dark-gray gouge with fragments (~13 cm), fault breccia(~10 cm), dark-gray gouge with fragments (~34 cm), gray gouge(~25 cm), calcite vein (~10 cm) and fault breccia (~44 cm). Accordingto the logging data, the gouge layers bear dip directions of N290, anda dip angle of 74. The fault zone is a pure thrust as indicated by theslickensides in the third gouge layer that bears the same dip directionas the fault plane.

The FZ233 fault zone consists of a group of fractures with SE strikingdirection and moderately tilted, it is mainly present at depths of 234.2236.05 m. The logging parameters such as the apparent resistivity anddensity decrease, but the well diameter, wave velocity, interval acoustictransit time and neutron porosity increase here.

The rockswith a natural gamma index N100 API in FZ970 aremostlyfault gouge. The siltstone shares a natural gamma index between 90 and100 API. The argillaceous siltstone's gamma radiation is b90 (8090 API) while the sandstone has the lowest radiation (b80 API). Theblack gouge has the highest gamma radiation, low resistivity anddensity but high porosity.

6. Discussion

6.1. High natural gamma radiation within all fault zones

In all three main fault zones (FZ233, FZ590759, and FZ970), thefault gouge layers record higher gamma radiations (Figs. 4, 9 and 10),especially the black gouge layers. The highest gamma radiation(140 API) comes from a black gouge layer in the third fault rock unitin FZ970, the YBF zone (Fig. 4). The gamma radiation peaks (120 API)where the thin grayish gouge layers appear (595.5693.5 m) withinthe fault breccia zone, such as in FZ608, FZ621, FZ628, FZ639, FZ646,FZ655, FZ669, FZ678 and FZ759. A possible interpretation is that thenatural gamma radiation increases with the wall rock clay content, orincreases as the grain size decreases. For the fault breccia, cataclasiteand fault gouge that have the same protolith, the fault gouge has thesmallest grain size and the highest clay content, therefore it has thehighest gamma radiation. In WFSD-1, the high gamma radiation is acritical criterion to judge whether it is fault gouge or not. However,this is not what has been found in the Taiwan drilling project (TCDP),where the gamma radiation in fault gouges was not abnormal. Conse-quently, the ultrahigh gamma radiation inWFSD-1 fault gouges is relat-ed not only to the fault gouge itself, but also to the protolith.

0 3

tron (%)

ftivi

96 H. Li et al. / Tectonophysics 619620 (2014) 861005.2.3.3. FZ970. FZ970 fault core (zone) ranges from 970.26 to971.78 m-depth (Fig. 10), is composed of gray siltstone and shale(Fig. 3), and clearly belongs to the late Triassic Xujiahe Formation.FZ970 from top to bottom (Fig. 10) consists of black fault gouge(~51 cm), gray fault breccia (~66 cm), and black fault gouge (~35 cm).

FZ233

90 120 150(mm)

Borehole Diameter

30 50 70(API)

Natural Gamma

100 300 500 700

Apparent Resistivity(Ohm.m)

50 100 150 200(us/ft)

P-wave Velocity

10 2

Neu

225

227

229

231

233

235

237

239

241

243

Fault Rocks

Dep

th (m

)

223

a b c d eFig. 9. Fault rocks (a)withwell diameter (b), natural gamma ray radiation (c), apparent resis

magnetic susceptibility (j) logs from FZ232 in WFSD-1 (228238 m-depth), and drilling core s6.2. Low density and resistivity within all fault zones

The density and porosity data are not available for the depths 594780 m in WFSD-1. Therefore, we cannot retrieve information on thefault zones' general density and porosity. But the data above 594 m

0 30 60 90 120 150

Magnetic Susceptibility(10 SI)-4

0 40 50

Porosity

0 100 200

Focused Resistivity(Ohm.m)

1.5 2.0 2.5 3.0

Compensated Density (g/cm3)

30 60 90 120

Self-potential(mv)

WFSD-1 Core

232.50 m

233.33 m

Dar

k-G

ray

Faul

t Gou

ge +

Bre

ccia

Gra

y Fa

ult G

ouge

g h i j kty (d), P-wave velocity (e), porosity (f), focused resistivity (g), density (h), self-potential (i),

ample from 232.50 to 233.33 m-depth (k).

show that FZ590 has a low density and high porosity, while the data forthe whole core indicate that all of the fault zones commonly have a lowdensity and resistivity, and a high porosity and P-wave velocity, partic-ularly the FZ233, FZ465, FZ590 and FZ970 fault zones. The apparent re-sistivity is extremely low along the YBF zone (Figs. 4, 9 and 10). Ingeneral, the well diameter, P-wave velocity and neutron porosity in-crease in the fault zone, while other logging parameters such as densityand resistivity decrease (Figs. 4, 8, 9 and 10), even though in a few smallfault gouge zone, the P-wave velocity decreases (Fig. 5). A possible ex-planation is that because both the fault gouge and fault breccia areweaker than the wall rocks, they can easily collapse to widen the welldiameter, lower the density and resistivity aswell as increase the poros-ity and theuid content. However, in FZ233, FZ590 and other secondaryfault zones, the fault gouge and fault breccia are almost intact judgingfrom the core continuity and ultrasonic image. Indeed, the density andresistivity are similarly low and the porosity and wave velocity arehigh. Therefore, we cannot assure the cause-and-effect relationship be-tween the logging response and the well diameter variation.

6.3. High magnetic susceptibility within the major fault zones

Themagnetic susceptibility varies greatly in the fault rocks ofWFSD-1but is generally higher than that of the wall rocks. The peak susceptibilityappears near the fault gouge zone and attenuates to a minimum at thenearby fault breccia (Figs. 4, 8, 9 and 10). The magnetic susceptibilityvariations may be inuenced by the distance to the main fault plane,due to the fact that the fault gouge which developed on the fault planehas the highest magnetic susceptibility, i.e. the further the fault rocksfrom the fault plane, the weaker the magnetic susceptibility. This is alsowhat was found in TCDP (Hirono et al., 2008; Mishima et al., 2006;Tanikawa et al., 2008), where the magnetic value was determined bythe type of magnetic minerals, the mineral amount and the grain size.

mineral intomagneticminerals, thus increasing themagnetic susceptibil-ity in the fault gouge (Hirono et al., 2006, 2007; Kano et al., 2006;Mishima et al., 2006; Pei et al., 2010; Tanikawa et al., 2008). Additionally,the grain size degraded by the shear force may also lead to an increase inmagnetic susceptibility. The Principal Slip Zone (PSZ) in WFSD-1 drillingcores has highmagnetic susceptibility (Li et al., 2013), therefore, the highmagnetic value in fault gouges can be considered as evidence of faultactivity.

Note that the very high values of magnetic susceptibility at~594 m-depth (Fig. 11j) were caused by the metal from the jammeddrilling tools in the mashed fault gouge (Fig. 11m).

6.4. Characterization and width of the YingxiuBeichuan fault (YBF) zone

There are exactly six sections in the YBF zone with different loggingresponses. The response in the upper part (595.48602.65 m) of thedark grayish fault breccia zone (595.5693.5 m) is different from thatin the lower part: the natural gamma radiation (NGR) and P-wave veloc-ity are relatively low,while the self-potential and apparent resistivity arehigh, with the high resistivity being totally different from a normal faultzone. However, while sandstone is observed at the same depth in thecores, sandstone breccia is present at the surface outcrops (Wang et al.,in this issue), therefore, we believe that the sandstone at 595.48602.65 m-depth is actually sandstone breccia in the fault breccia zone.

From top to bottom, the logging responses of the ve different faultrock sections in the YBF zone are: cataclasite with low P-wave velocity,NGR and self-potential (575.7585.75 m); black fault gouge zonewhichcontains several layers of fault breccia (585.75595.5 m), with highNGR and P-wave velocity and low self-potential and resistivity; darkgrayish fault breccia zone with multiple gouge layers (595.5693.5 m), where NGR and P-wave velocity are high whereas resistivityis low; grayish fault breccia zone (693.5751 m), with lowNGR, P-wave

on Po(%)

40 6

f

97H. Li et al. / Tectonophysics 619620 (2014) 86100The intense heat generated by earthquakes may transform the original

(mm)Borehole Diameter

(API)Natural Gamma Apparent Resistivity

(Ohm.m) (us/ft)P-wave Velocity Neutr

Fault Rocks

50 100 150 200959

961

963

965

967

969

971

973

975

977

979

981

983

30 90 150 200 400 600 40 80 120 0 20

Dep

th (m

)

a b c d e

Fig. 10. Same as in Fig. 9 from FZ970 in WFSD-1 borehole (966976 m-depvelocity and resistivity; black fault gouge zone with fault breccia (751

Magnetic Susceptibility(10 SI)-4

rosity Focused Resistivity(Ohm.m)

Compensated Density (g/cm3)

Self-potential(mv)

0 80 2 4 6 8 1.0 2.0 3.0 -35 -25 -15 0 30 60 90 120150

FZ970

WFSD-1 Core

969.93 m

970.93 m

Blac

k G

ouge

Sand

ston

eFa

ult B

recc

ia

g h i j k

th), and the drilling core sample from 969.93 to 970.93 m-depth (k).

759 m), where NGR and P-wave velocity are high while apparent resis-tivity is low. The apparent length of the fault zone is 183.3 m in thedrilling cores, because of the slight tilt of the drilling hole ~6371 (Liet al., 2013), yielding the real thickness of the fault zone to be 9095 m.

6.5. Relationship with the 2008 Wenchuan earthquake (slip zone of theWenchuan Earthquake)

The plane or zone of slip that was activated during the 2008Wenchuan earthquake has not been identied in this study. However,in the temperature measurements from WFSD-1, Li et al. (2013) ob-served a slight peak around FZ590 and concluded that the increase oftemperature has been produced by frictional heating during the earth-quake. They found a 12 cm-thick slip zone at 590 m-depth, and sug-gested that it is associated with the 2008 Wenchuan earthquake. Theyreported high magnetic susceptibility, high seismic velocity and lowelectrical resistivity, and a major stress orientation anomaly aroundFZ590 from geophysical logs from WFSD-1, suggesting that theshallowest fault zone was most likely related to the 2008 Wenchuanearthquake.

The main fault zone was constrained at the boundary between vol-canic and sedimentary rocks (Li et al., 2013), which is also what wefound in the logging data here. Fig. 11 shows that the well diameterbecomes irregular at depths of 585594 m, with a larger diameter at586590 m and a narrower one at 591594 m. Correspondingly, theNGR increases from 60 to 90 API, the apparent resistivity drops from2000 to b100 m, the density decreases from 2.6 to 2.4 g/cm3, the in-terval acoustic transit time increases from 60 to100 s/ft, and the neu-tron porosity increases from 2030% to 4050%. The free-potentialincrease reects some permeability. All these parameters show not

By analyzing the ultrasonic image of the side well, 29 samples werecollected at depths of 585594 m, 19 of them share similar occurrences,with an average inclination direction of N305 and a dip angle of 71.Those occurrences are almost equal to the occurrence of the co-seismic surface rupture plane near the ground surface at Hongkou vil-lage in the southern part of the YBF, and attest that the fault zone at585594 m-depth is the co-seismic fault zone of the Wenchuan earth-quake. Consequently, the characteristics of theWenchuan earthquake'sPSZ at 590 m-depth are N305, with an average dip angle of 71, i.e. theWenchuan earthquake fault (YBF) is a high angle thrust fault (Li et al.,2013) as viewed from the southern part of the YBF in Hongkou village.

6.6. Fracture distribution and orientation in WFSD-1

An average of 10 fractures per meter are present in the cores ofWFSD-1 (Fig. 4j), with a maximum fracture density of 70/m. Part ofthe cracks was caused by the drilling process, so that the crack densityin Fig. 4 appears slightly larger than it is in reality. However, the fracturedistribution trend is similar and the fracture occurrence revealed by ul-trasonic images is what occurs at depth. The ten point diagrams (lowerhemisphere) of the fracture directions are based on the fracture statis-tics at different depths, with a 100 m interval. Unfortunately, the frac-ture statistics at 594780 m-depth is missing since no ultrasonicimages are available there.

In Fig. 4k, the dominant fracture occurrence in the drilling coresabove 600 m is dipping south with a dip angle of 60, and change tothe NE with a dip angle of 6183 at depths below 780 m. The upperpart represents the fracture characteristics in the Pengguan complex,i.e. the hanging wall of the YBF, while the part below 780 m reects

sedstivity

.m)20

Cara

y

sist79

98 H. Li et al. / Tectonophysics 619620 (2014) 86100only the lithological variations, but also the features of the main faultzone. The main fault zone is located at depths of 585.75594.5 m, andis mainly composed of fault gauge and fault breccia. As discussedabove, the temperature logging data were also abnormal at the samedepths, with a positive peak at 585 m (0.15 C, Fig. 2e).

FZ590

579

581

583

585

587

589

591

593

595

597

599

601

(mm)

BoreholeDiameter

(API)

NaturalGamma

Apparent Resistivity(Ohm.m) (us/ft)

P-waveVelocity

NeutronPorosity

(%)

FocuResi(OhmFault Rocks

60 90 120 150 0 30 60 90 120150 0 100 200 300 400 50 100 150 200 0 20 40 60 0 10

Dep

th (m

)

a b c d e f gFig. 11. Fault rocks (a) with well diameter (b), natural gamma ray radiation (c), apparent re(i), magnetic susceptibility (j), and temperature (k) logs from FZ590 inWFSD-1 borehole (5

594.57 m-depth (m).Dar

k G

589.65 m

594.57 m

Faul

t Bre

ccia

h i j k l mivity (d), P-wave velocity (e), porosity (f), focused resistivity (g), density (h), self-potential601 m-depth), and drilling core samples from 589.04 to 589.65 m-depth (l) and 593.57 tothe fracture characteristics in the Xujiahe Formation. Theoretically, thedistribution of fractures in the drilling cores reects the eld stress dis-tribution, thus, the hanging wall and footwall of the YBF have differentstress eld characteristics, indicating that the Pengguan complex isnot an autochthonous geological unit, or in other words, that the

Magnetic Susceptibility

(10 SI)-4

Compensated Density

(g/cm )Self-potential

(mv)Temperature

(C)30 2.0 2.5 3.0 -30 -10 0 10 0 500 24.4 24.6 24.8 25.0

0.15C

1000

Blac

k Fr

esh

Gou

geBl

ack

Gou

geta

clasit

e - G

ouge

WFSD-1 Core

589.04 m

PSZ

593.57 m

Blac

k G

ouge

3

99H. Li et al. / Tectonophysics 619620 (2014) 86100Pengguan complex has overlapped here from somewhere far away,rather than being the result of the YBF repeated activity.

7. Conclusion

The Wenchuan earthquake Fault Scientic Drilling project (WFSD)provides a unique opportunity to study earthquake mechanisms. Bymeans of analyzing the logging data of the 1200 m deep borehole 1and studying the geological features in the drilling cores, several conclu-sions were obtained:

(1) The geothermal gradient for the entire hole is 2.05 C/100 m. Thelogging responses of the Pengguan complex (32585.75 m) andXujiahe Formation (585.751200 m) are different: the formerhas a relatively higher density, neutron porosity and apparent re-sistivity than the latter. The density decreases as the gamma radi-ation increases in the Pengguan complex, whereas, in the XujiaheFormation the density increases with the gamma radiation. TheXujiahe Formation has a high gamma radiation and geothermalgradient (2.15 C/100 m compared with 1.85 C/100 m for thePengguan complex).

(2) Most of the fault zones uncovered in WFSD-1 have high gammaradiation, especially the fault gouge layers. It is different fromthe results obtained in TCDP (Taiwan drilling project). The highgamma radiation in the WFSD-1 fault zones may be related to li-thology.

(3) All themajor fault zones inWFSD-1 have lowdensity and resistiv-ity, but high porosity and P-wave velocity. The lower densitiesmight have resulted from extensive fracturing and cracks withinthe fault zones and/or loss of atoms with high atomic number,but do not likely reect an articial washout effect.

(4) All the fault-related rocks correspondwell with the highmagneticsusceptibility, which appear in the fault gouges. A possible expla-nation is that the massive heat released by fault friction boostedthe formation of new magnetic minerals, or the enormous shearforce crushed the fault gouge particles into smaller grains.

(5) The YBF zone exposed inWFSD-1 can be subdivided into ve dif-ferent parts based on different logging responses, each of themcorresponding to certain fault rocks. The apparent thickness ofthe fault zone is about 183 m while the real thickness is only9095 m.

(6) The high gamma radiation, porosity and P-wave velocity, but lowapparent resistivity and positive temperature anomalies all indi-cate that the main Wenchuan earthquake fault plane is locatedat 585.75594.5 m-depth, with an average inclination and dipangle of N305, and 71, respectively. The Wenchuan earthquakefault is a high angle thrust fault as viewed from the southern partof the YBF.

(7) The fractures in the Pengguan complex in the hanging wall of theYBF generally trend south with an average dip angle of ~60,whereas the fractures in the Xujiahe Formation in the footwalltrend NE, with a dip angle of 6183. It shows that the stresseld in the hanging wall and footwall of the YBF is totally differ-ent, which also implies that the Pengguan complex is not anautochthonous material.

Acknowledgments

We appreciate the help and support of Xuelong Wang, Shiyou Hu,Wei Zhang, Jun Jia and Lasheng Fan of the WFSD Center. Special thanksto the Faculty of the geological team 403, Sichuan Geology and MineralBureau, for their drilling work. We are grateful to Huihua Li and YongZhang from the geological team 405 for their excellent logging work.This research was supported by the National Science and TechnologyPlanning Project of China, the Wenchuan earthquake Fault Scientic

Drilling project (WFSD) and the National Natural Science Foundationof China (41330211). We also thank two anonymous reviewers fortheir comments which greatly improved this manuscript.

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100 H. Li et al. / Tectonophysics 619620 (2014) 86100

Structural and physical property characterization in the Wenchuanearthquake Fault Scientific Drilling project hole 1 (WFSD-1)1. Introduction2. Geological setting of the Wenchuan earthquake fault zone3. Drilling procedure and WFSD-1 core characteristics3.1. Drilling procedure3.2. Structures, lithologies and fault rocks of the drilling core samples

4. Methodology for geophysical logs and data acquisition5. Rock physical properties from geophysical logs5.1. Conventional logging5.2. Subsurface structure, physical properties and log units for WFSD-15.2.1. Unit I (Pengguan complex)5.2.2. Unit II (Xujiahe Formation)5.2.3. Unit III (fault zones): fault zone structures and physical properties5.2.3.1. YBF(FZ590759)5.2.3.2. FZ2335.2.3.3. FZ970

6. Discussion6.1. High natural gamma radiation within all fault zones6.2. Low density and resistivity within all fault zones6.3. High magnetic susceptibility within the major fault zones6.4. Characterization and width of the YingxiuBeichuan fault (YBF) zone6.5. Relationship with the 2008 Wenchuan earthquake (slip zone of the Wenchuan Earthquake)6.6. Fracture distribution and orientation in WFSD-1

7. ConclusionAcknowledgmentsReferences