Tectonophysics 600 (2013) 108–115

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Tectonophysics

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Fluid pressures and fluid flows from boreholes spanning the NanTroSEIZEtransect through the Nankai Trough, SW Japan

J. Casey Moore a,⁎, Myles Barrett b, Moe Kyaw Thu c

a Earth and Planetary Sciences Department, University of California, Santa Cruz, CA 95064, USAb Hess Indonesia, The Energy, 11th–12th Fl., SCBD Lot., 11A Jl. Jend., Sudirman Kav. 52-53, Jakarta 12190, Indonesiac Center for Deep Earth Exploration, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan

⁎ Corresponding author.E-mail address: cmoore@pmc.ucsc.edu (J.C. Moore).

0040-1951/$ – see front matter © 2013 Elsevier B.V. Allhttp://dx.doi.org/10.1016/j.tecto.2013.01.026

a b s t r a c t

a r t i c l e i n f o

Article history:Received 4 June 2012Received in revised form 11 January 2013Accepted 27 January 2013Available online 4 February 2013

Keywords:TectonicsFluid flowFluid pressureAccretionary prismsEarthquakes

IODP Expedition 314 acquired annular pressure while drilling measurements in six holes extending from theouter forearc basin to the base of the trench slope. These data provide pressures inside the borehole near thebit during drilling; the pressures reflect the cuttings load in the borehole, and the viscous resistance to flow offluids up the borehole due to pumping from the rig floor and due to fluid exchange with the formation. Theforearc basin site provides a reference locality that extends to 1402 m and whose pressure curve is apparentlycontrolled dominantly by the cuttings load and the rig-floor pumping rate. All other holes show at least initialpressure curves that are very similar to that at the forearc basin site, despite pumping rates varying by about20–30%. Some small variations in pressure curves can be positively correlated to the penetration rate that con-trols cutting load. Two holes crossing a fracture zone show pressure anomalies extending to above-lithostaticconditions, and modeled fluid influx rates of 3000 l/m or 150% of the rig-floor pumping rate. A third hole, prob-ably in the same highly overpressured zone, shows a near lithostatic pressure value just prior to losing the bot-tom hole assembly due to stuck pipe. The extraordinarily high pressures occur in the upper portion of thehanging wall of the megasplay fault zone and may reflect residual conditions from the 1944 M 8.1 earthquake.A penetration of the lower boundary of the megasplay fault zone shows only minor fluid pressure anomaliesaround the fault surface. A hole through the frontal thrust records fluid pressure anomalies in sandy sedimentsof the footwall, apparently due to expulsion of fluids from loading by the hanging wall.

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1. Introduction

Because fluids affect many aspects of deformation, diagenesis, andmetamorphism, understanding their distribution in the subsurface isof paramount importance (Fyfe et al., 1978). Fluid pressure variationsare critical in driving fluid flow in the crust and any geological conse-quences of flow (Ingebritsen et al., 2006). Accordingly, we have com-piled the annular fluid pressures observed during drilling along theNankai Trough Seismogenic Zone Experiment (NanTroSEIZE) transectacross the forearc and accretionary prism of the Nankai Trough off theKii Peninsula of SW Japan. Our transect spans from the outer forearcbasin to the base of the trench slope (Figs. 1, 2). The goal of the paperis to present variations in annular pressure while drilling (APWD) prin-cipally across four sites that crossedmajor faults,while using the forearcbasin site as a reference APWD curve through a section where faultactivity is low. A prior manuscript (Moore et al., 2012) focuses on twoholes with very high pressures, discusses the technical details ofAPWD and models the pressure response of the boreholes. In contrast

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this paper focuses on the geologic correlations of all the pressure curvesacross the NanTroSEIZE transect.

1.1. Annular pressure while drilling, measurement while drilling tools,and torque

The oil industry has developed tools for measuring fluid pressurewhile drilling in the borehole annulus for safety reasons and to properlybalancefluid pressureswithin boreholes to those in the adjacent forma-tion (Desbrandes, 1990). The data on fluid pressure is measured a fewto greater than 10 m above the bit, recorded down-hole, and also com-municated to the surface while drilling by pressure waves transmittedthrough the borehole fluid (Fig. 3). Other borehole parameters mayalso be transmitted to the surface during drilling. Commonly the mea-surement while drilling (MWD) tool is part of a series of loggingwhile drilling (LWD) tools that provide a complete set of logs, includingborehole resistivity imaging and ultrasonic caliper (Fig. 3).

During IODP Expedition 314 themeasurement while drilling tool wasutilized at all boreholes. The pressuremeasured in the borehole is due to acombination of the density of thefluid in the borehole and up through theoceanic water column, plus any viscous resistance to the flow of the fluidthrough the borehole annulus. Seawater was the drilling fluid in all the

136°20'E 136°30' 136°40' 136°50' 137°00'32°50'

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Nankai Trough

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~4.1-6.5 cm/y

Philippine SeaJapan

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Figure 2

Fig. 1. Locations of sites drilled during Expeditions 314, 315, and 316, with yellow arrows indicating estimates of convergence directions across trench (Tobin et al., 2009).

Inactive déco tnemell

Décollement

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Fig. 2. Interpreted seismic data showing tectonic setting of sites in Fig. 1 (Moore et al., 2009). BSR marks bottom simulating reflector. PTZ refers to proto-thrust zone.

109J.C. Moore et al. / Tectonophysics 600 (2013) 108–115

adnVISION(density, porosity, ultrasonic caliper)

geoVISION(resistivity, gamma ray)

sonicVISION(velocity, traveltime)

seismicVISION(check shot interval velocity)

PowerPulse MWD(annular pressure,

direction, and inclination)

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13.2 Annular or Borehole Fluid Pressure

28.2 Ultrasonic Caliper

Fig. 3. Tool schematic for maximum LWD tool assembly used during Expedition 314logging (Expedition 314 Scientists, 2009a).

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C0001A

C0001D

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Annular Pressure While Drilling (MPa)

hydrostatic

Fig. 4. Annular pressure while drilling for all sites plotted with a common pressureorigin. Note the standard APWD gradient shown by Holes C0002A, C0004B, C0006A,and the shallower portions of C0001A, C0001D, and C0003A. The deeper parts ofHoles C0001A and C0001D and C0003A diverge from this standard gradient and are be-lieved to have penetrated fracture zones that are injecting large volumes of fluids intothe boreholes. mbsf=meters below sea floor.

110 J.C. Moore et al. / Tectonophysics 600 (2013) 108–115

holes but the cuttings load increases the fluid density and likewise theborehole pressure. The geometry of the drill string, and especially its bot-tom hole assembly (BHA) can affect fluid flow and pressure. Any forma-tion fluid added to the borehole will increase the APWD in excess ofthat created by pumping from the rig floor. Loss of fluid to the formationwould decrease APWD. Thus the APWD curves provide a basis for under-standing fluid flow into and out of the formation (Ostermeier et al., 2000;Ward and Andreassen, 2000).

Torque represents the frictional resistance to rotation of the drillstring and is measured at the rig floor. Torque generally increasesgradually with depth. Sharp increases in torque can indicate hole col-lapse, and may be a prelude to getting stuck. Conversely a hole canwashout, become enlarged, and if the cuttings are removed fromthe hole, the torque can decrease.

In this paper we present pressure and torque data from six holes atfive sites. (Figs. 1, 4). All holes are drilled with a bit 8.5 in. in diameter.The fluid pressure measurement was made at 13 m above the bit inHoles C0001D, C0002A, C0003A, C0004B, 7 m above the bit in HoleC0001A and 3 m above the bit in Hole C0006A. Following industry-standard procedure, we plot the pressure measurement at the depththat the pressure sensor is located in the MWD tool (3–13 m abovethe bit, depending on the components of the BHA). In contrast, torque,is plotted at bit depth. However, it is possible that the pressure mea-surement records pressure changes occurring at the bit before the pres-sure sensor reaches that depth. A pressure pulse travels through thedrilling fluid (mostly seawater) at the velocity of sound; therefore, theresponse at theMWD pressure transducer should be essentially instan-taneous to a fluid influx or loss at the bit.

1.2. Geologic setting of the Nankai Trough Subduction Zone Transectacross the Kumano Forearc

The subduction of the Philippine Sea plate beneath southwest Japanforms the Nankai Trough and the associated accretionary prism. In theKumano region, estimates of the rate of subduction range from 4 to6.5 cm/year along azimuths of 300 to 315 deg. (Miyazaki and Heki,

2001; Seno et al., 1993; Zang et al., 2002). Along the NanTroSEIZEtransect, the subduction direction is rotated about 15 to 30° counter-clockwise from the dip azimuth of the trench slope, so there is a compo-nent of obliquity (Fig. 1). The continental margin originated both fromthe deposits on the oceanic plate, that were structurally emplaced toform the accretionary prism, and sediments accumulated on the slopeand in the forearc basin on top of the accretionary prism (Fig. 2)(Kinoshita et al., 2009; Saito et al., 2010). Where cored or logged, theaccretionary prism and forearc basin are dominated by mudstone andlocally sandy turbidites (Underwood and Moore, 2012). Large-scalethrust faults characterize the structure of the margin (Moore et al.,2007, 2009). Large, apparently active, megasplay (out-of-sequencethrust) faults emerge along the inner trench slope (Moore et al., 2007)and may have slipped during the M 8.1 earthquake that occurred in1944 (Baba and Cummins, 2005). Sites C0001, C0003, and C0004 lie inthis megasplay fault zone (Fig. 2).

1.3. Annular pressure while drilling measurements

We examine the pressure while drilling along a transect from theforearc basin (Site C0002) to the tip of the accretionary prism at SiteC0006 (Figs. 1, 2). This order allows us to begin with the backgroundenvironment of the forearc basin and proceed through the faulted ac-cretionary prism with a more vigorous fluid pressure response.

A plot of all pressure data across the transect shows a variety ofpressure-depth curves (Fig. 4). For example Site C0002 shows a rela-tively uniform increase in pressure, although at a gradient higher thanhydrostatic. Sites C0004 and C0006 have overall pressure gradients sim-ilar to Site C0002 but punctuated by small fluid pressure events. Finally,Sites C0001 and C0003 show large positive divergences from the gradi-ent defined by C0002.

1.4. Site C0002

1.4.1. DescriptionSite C0002 penetrated 936 m below sea floor (mbsf) into the

forearc/slope basin sequence and an additional 436 mbsf into the subja-cent accretionary prism (Expedition 314 Scientists, 2009c). The section

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Hole C0001AHole C0001DHole C0002AHole C0003AHole C0004BHole C0006A

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Rig Floor Pumping Rate (l/m)

Fig. 6. Summary of pump rates for all sites. Note that the total variation in pumping rate isabout 20–30%, yet the baseline background pressures at all sites are very similar. The largepressure excursions in Holes C0001A and C0001D are associatedwith pumping rates thatare lower than other sites. Also, the pumping rates at these sites did not change signifi-cantly during the fluid influx estimated to occur at about 500 mbsf.

111J.C. Moore et al. / Tectonophysics 600 (2013) 108–115

was dominated by mud/mudstone with silty and sandy turbidites(Expedition 315 Scientists, 2009b). The base of the section is lateMiocene in age and up to 6–7 my old (Expedition 315 Scientists,2009b).

The APWD curve for Site C0002 shows a systematic increase inpressure. The increasing pressure through the entire sequence risesalong a uniform gradient that is higher than hydrostatic (Fig. 5).Below the forearc/slope basin deposits, in the accretionary prism,the pressure curve shows more small-scale irregularity. Overall thetorque values are low; however, they trend higher in the accretionaryprism with one spike reaching 10 kNm.

1.4.2. InterpretationThe uniform increase in pressure is interpreted as a response to the

increased cutting load and viscous resistance to flow up the annulus.The pressure gradient in the forearc basin deposits (0–936 mbsf) istaken as the standard riserless APWD gradient for the NanTroSEIZEtransect. This standard APWD gradient is similar to those at SitesC0004, C0006 and the shallower parts of C0001 and C0003 (Fig. 4).The pumping rates at all sites vary by 20–30% (Fig. 6) but show no im-pact on the pressure curves. Apparently the APWD data are insensitiveto variations in fluid influxes of this magnitude. The standard APWDgradient is used as the reference in which we infer no measureablefluid influx or loss other than that due to pumping. The pressure curvein the accretionary prism shows small pressure spikes, perhaps becausethe higher sand content in this unit could provide sharp pulses of fluidinflux. The increase in torque in the accretionary prismand its increasedvariability could be due to the sandy section collapsing into the hole.The poor recovery during coring is consistent with this interpretation(Expedition 315 Scientists, 2009b).

1.5. Site C0001

1.5.1. DescriptionSite C0001 lies in the hanging wall of the megasplay fault zone

(Fig. 2). Mud and mudstone dominate the lithology of Site C0001 inthe accretionary prism; sands occur in the basal intervals of theslope apron, at depths to 207 mbsf (Expedition 314 Scientists, 2009b;Expedition 315 Scientists, 2009a). Cores from Hole C00011 to 458 mbsfshow small-scale faults of normal, thrust, and strike-slip displacementwith normal faults being most dominant and latest. (Expedition 315Scientists, 2009a; Kinoshita et al., 2009).

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Fig. 5. Site C0002 is located in the forearc basin and was a stable borehole, penetrating to 1rising above hydrostatic, due to increasing cuttings load and viscous resistance to annular fl

APWD curves at Holes C0001A and C0001D are uniquely high(Moore et al., 2012). The pressure curves follow the standard APWDgradient to about 375 mbsf and then transition to lithostatic to abovelithostatic fluid pressures by 500 mbsf through a series of pressurespikes (Fig. 7). Both holes settle back to an under-lithostatic pressureby 687 mbsf; this pressure increases to 1000 mbsf along a smooth,over-pressured trajectory with a gradient higher than the standardAPWD gradient. The zone of rapid fluid pressure increase lies at theup-dip termination of an irregular zone of bright reflectors (Fig. 7).

A small but clear variation occurs in pressure between HolesC0001A and C0001D down to 370 mbsf; this pressure difference iscorrelated with a rate of penetration that is twice as fast in C0001A(~60 m/h) verses C0001D (~30 m/h) at depths less than 500 m.

Logging data provide structural information about the borehole thatcan be linked to its pressure response (Chang et al., 2010; Expedition314 Scientists, 2009b; Moore et al., 2012). In Hole C0001D boreholeimages, resistivity, and velocity data show discrete thin low resistivity,low velocity zones from about 425 to 500 mbsf. A more extensivelow velocity/resistivity zone characterizes the borehole from 490 to630 mbsf. Enlarged images of this interval, (e.g. 520–550 mbsf) show

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402 m. The APWD here is our best example of a standard APWD gradient: a pressureow with depth. Seismic image from Moore et al. (2009). kmbsl=km below sea level.

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Fig. 7. Pressure and torque data from Holes C0001A and C0001D. These holes show extraordinary pressure pulses centered around 500 mbsf (Moore et al., 2012). Note that torque isextraordinarily high in Hole C0001A, however the major increase in torque is recorded about 25 m below the sharp increase in fluid pressure. Therefore, it is unlikely that pluggingof the annulus by sloughed sediment was completely responsible for the elevated fluid pressure. Rather an initial influx of formation fluid is suspected. Seismic image fromMoore etal. (2009).

112 J.C. Moore et al. / Tectonophysics 600 (2013) 108–115

low resistivity zones in a variety of orientationswithwidths of cm todmscale. The low resistivity areas in this image could represent fluid-richshear zones, extensional structures developed due to shearing, orextensional hydrofractures (Moore et al., 2012).

1.5.2. InterpretationThe increase in annular pressure in the 375 to about 500 mbsf

range is explained by fluid influx through fractures recognized inthe borehole logs (Chang et al., 2010; Expedition 314 Scientists,2009b; Moore et al., 2012). The low resistivity and velocity, probablyhighly fractured, interval from 490 to 630 mbsf encompasses most ofthe depth interval where the fluid pressure exceeds lithostatic in HoleC0001D.

Both Holes C0001A and C0001D show a torque increase in the zoneof rapid fluid pressure increase, with the values in C0001D being muchhigher than C001A (Fig. 7). This may be explained by sediment fallinginto the borehole and temporarily restricting the annulus. However,the pressures beyond 687 mbsf in Hole C0001D assumed a smooth,sublithostatic, but overpressured trajectory and torque returned to amore normal level; in Hole C0001A pressures had returned to a smoothoverpressured but sublithostatic level by 525 mbsf; by 687 mbsf annu-lar constrictions in both holes were apparently removed by wiper tripsand other hole cleaning activities.

The sharp increase in pressure in both holes at about 500 mbsf mayreflect a large influx of fluid. In Hole C0001A, hydraulic modeling of thepressure increase at 490 mbsf suggests an increase in flow rate of about3000 l/m, over and above the rig floor pumping rate of about 2000 l/m(Moore et al., 2012). The modeling software (WellPlan by Halliburton)treats the borehole annulus as a conduit through which a fluid volumeis passed to recreate the observed overpressures Moore et al. (2012).The high pressures cannot be explained by high pumping rates becausethe rates at Holes C0001A and C0001D are lower than those of the othersites in this transect (Fig. 6). The oil industry has experienced similar

large pressure increases, fluid flows, and associated hole problemsfrom shallowly-buried sands drilled in riserlessmode in theGulf ofMex-ico (Ostermeier et al., 2000, 2002). These sands contributed large vol-umes of fluid to the boreholes, ultimately causing failure in some cases.

Twenty-five m below their initial increase the supralithostatic an-nular pressures in Hole C0001D are associated with high torquevalues, probably due to sloughing into the borehole and restrictionof the annulus. The very high pressures observed in Hole C0001Dwere not appropriate for modeling because the model assumes a con-stant hole diameter. It is possible that the very high pressures injectedsome fluid into the borehole wall.

The higher pressure (to 370 mbsf) in Hole C0001A, relative toC0001D, is attributable to a higher cutting load that would occur dur-ing a higher penetration rate at a similar rate of pumping.

1.6. Site C0003

1.6.1. DescriptionSite C0003 is located about 1.1 km downslope from C0001. Because

the LWD tool string was lost at a total depth of about 500 mbsf, infor-mation is limited to that communicated up the borehole in real timeand to drilling parameters recorded on the rig floor (Expedition 314Scientists, 2009d). The hole penetrates a moderately strong seismic re-flector between 400 and 450 mbsf (Fig. 8). Resistivity and gamma raylogs suggest that the accretionary prism here is composed of mudstone.Pieces of late Miocene mudstone with slickenlined exteriors were re-covered from the broken end of the drill pipe upon its recovery (Tobinet al., 2009). These resemble sheared rocks characteristic of faults anddamage zones around faults. The source depth of the sheared rock is un-known but it is probably somewhere near the broken end of the pipe at300 mbsf.

The pressure increases along the standard APWD gradient until425 mbsf (Fig. 8). At this depth the pressure increases modestly,

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Fig. 8. Pressure and torque data from Hole C0003A. After remaining at the background baseline pressure until below 425 mbsf, the pressure curve sporadically increases to a finalsurge of 3 MPa over the baseline. Black arrow shows location of moderately strong seismic reflector, and possible fault, at about 425 mbsf. Although the evidence is incompletebecause the LWD tool was lost in this hole, we suspect that his hole was in transition to a high-pressure regime similar to that at Holes C0001A and C0001D. Seismic imagefrom Moore et al. (2009).

113J.C. Moore et al. / Tectonophysics 600 (2013) 108–115

about 1 MPa higher than the background, and subsides by 445 mbsf.Several other pressure spikes in the 1 MPa range occur before reachingtotal depth of 526 mbsf where a pressure spike of about 3 MPa abovethe background occurs at about 513 mbsf, and declines by 520 mbsf. Ul-trasonic caliper data, available to a depth of 500 mbsf, shows in-gaugediameters with some instances of annular enlargement correlatingwith the pressure spikes. Torque increases irregularly below 425 mbsfuntil it reaches 7.5 kNm at 525 mbsf, where the pipe became stuck.

1.6.2. InterpretationThe APWD response at Site C0003 is similar to that at Site C0001. At

Site C0003, at 425 mbsf, the uniform increase in pressure is replaced byincreases in pressure with the final pressure surge being 3 MPa. Torquerises near the pressure increases; but, by the time the ultrasonic caliperreaches the depth of the pressure surge, the hole is enlarged in somebutnot all instances. Apparently any mudstone that fell into the annuluswas pulverized and circulated out. Some seismic reflectors believed tobe faults (Expedition 314 Scientists, 2009d) intersect the hole at thedepth of the pressure increases and at the intervals of hole enlargement.Hole enlargement correlating with some of the pressure increases sug-gests collapse of the borehole, perhaps from the pre-sheared fault rockor associated damage zones.

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Fig. 9. Seismic image, APWD and torque at Site C0004. This hole shows negligible fluid pressuis currently hydrologically inactive, in comparison to intervals at about 500 mbsf at Sites C

1.7. Site C0004

1.7.1. DescriptionSite C0004 lies near the seaward edge of themega-splay thrust zone.

This borehole penetrated 400 mbsf (Expedition 314 Scientists, 2009e)through one of the major megasplay thrusts. The section is mostlymud-mudstone with some thin sand and ash layers (Expedition 316Scientists, 2009a). The APWD curve is only slightly higher than hydro-static (Fig. 9). The lower half of the hole, spanning the basal thrust, ischaracterized by spikes in pressure to about 1 MPa above the back-ground pressure. Torque values are low throughout the hole withsome increase in variability below the basal thrust.

1.7.2. InterpretationSite C0004 shows smaller pressure anomalies than any other hole

penetrating a fault along the transect. The lack of notable fluid pressureanomalies may be due to the decreasing activity of this fault strand inthe last 1 my (Strasser et al., 2009). Similarly direct measurement offluid pressure at Site C0010, along a lateral extension of the fault atSite C0004, showed barely above hydrostatic values (Expedition 332Scientists, 2011).

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re anomalies around basal thrust of megasplay fault system. As seen by APWD this fault0001 and C0003. Seismic image from Moore et al. (2009).

FrontalThrust

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Fig. 10. Seismic image, APWD and torque at Site C0006. Fluid pressure increases in the 1–2 MPa range characterize the section below the frontal thrust. Logging results indicate thatthis section is dominated by sandy sediment. Yellow arrows indicate inferred lateral flow beneath the frontal thrust, probably due to the increasing overburden in a landwarddirection. Seismic image from Moore et al. (2009).

114 J.C. Moore et al. / Tectonophysics 600 (2013) 108–115

1.8. Site C0006

1.8.1. DescriptionSite C0006 penetrated the toe of the trench slope extending about

180–190 m below the frontal thrust into a trench channel complex.Above the frontal thrust the sediments are primarily mud/mudstonewith subsidiary sand intervals (Expedition 316 Scientists, 2009b).Below the frontal thrust the section is mostly sand and has beeninterpreted as a trench channel complex (Fig. 10) (Expedition 314Scientists, 2009f; Moore et al., 2009). The APWD increases along a uni-form gradient through the frontal thrust to total depth, almost exactlyalong the standard APWD gradient from Site C0002 (Fig. 4). Pressurespikes of up to 1 MPa occur from 50 m above to 150 m below the fron-tal thrust (Fig. 10). The torque values are modest through the intervalabove the frontal thrust and decline after about 770 mbsf below thefrontal thrust.

1.8.2. InterpretationAlthough Site C0006 does not show large fluid pressure anomalies

like Sites C0001 and C0003, the fluid pressure regime is consistentwith the tectonic setting. The spikes of fluid pressure around the frontalthrust are interpreted as pressure highs caused by a seaward flux offluid (Fig. 10). A seaward decreasing load of the landward-thickeninghanging wall of the frontal thrust is probably responsible for theseaward-directed flow. The trench channel complex probably providesa suitably permeable lithology to focus flow with the muddier upperplate capping the fluid migration. The decrease in torque in the under-thrust sequence suggests hole enlargement which is verified by theultrasonic caliper measurements (Expedition 314 Scientists, 2009f).

2. Discussion

2.1. Variations in annular pressure across the margin

The five sites discussed in this paper show significant contrasts inannular pressure. Site C0002 in the forearc basin is expectably lowand defines the background pressure gradient for a hole apparentlynot exchanging much fluid with the formation. Conversely SitesC0001 and C0003 show large variations in annular pressure reachingand exceeding lithostatic values. Sites C0004 and C0006 have onlymod-est pressure excursions above the background gradient defined by SiteC0002.

Why are the annular pressures so extreme at Sites C0001 andC0003? These sites lie in the upper portion of themegasplay fault hang-ingwall thatmay have undergone displacement in the 1944 earthquake(Baba and Cummins, 2005; Park et al., 2002). The megasplay fault zone

extends down-dip to low impedance, potentially water-rich, over-pressured sediment (Bangs et al., 2009; Park et al., 2010). Although dis-placement of any fault or fracture zone beneath Sites C0001 and C0003may have been small, the permeability may have been enhancedallowing the fracture network to be recharged with fluid from theknown subjacent deep sources. The abundance of overpressured fluidsis consistent with limited healing since the earthquake.

3. Conclusions

The NanTroSEIZE transect holes show a wide range in hydrologicactivity, from copious flow from fractured rocks at Site C0001 to min-imal fluid flow along a thrust in a related area at Site C0004. All holesshow a standard APWD gradient thatmodestly higher than hydrostat-ic at about 10.61 kPa/m. This standard APWD gradient is exceeded tolithostatic pressure values in the C0001 and C0003 Sites, and deviatedfrom to lesser degrees in other holes. Annular fluid pressures are in-sensitive to variations in pumping rate of 20–30%. Large influxes offluid at Site C0001 (i.e. 150% of pumping rate) were obvious in theAPWD curves and responsible for serious hole problems. The fracturedzones providing the fluid at Site C0001may had their permeability en-hanced during the 1944 M 8.1 earthquake that apparently localized inthe megasplay fault zone (Baba and Cummins, 2005).

Acknowledgments

We appreciate the efforts of the organizers of the KANAME meetingfor the opportunity to present this paper, both orally and in print. Wethank IODP member countries for supporting scientific ocean drillingand for their long-term commitment to the NanTroSEIZE project. Wethank the drilling and logging personnel of the Chikyu for their careful ef-forts from which this paper is derived. We also appreciate the input ofthe engineering staff at Center for Deep Earth Exploration, Japan Agencyfor Marine-Earth Science and Technology for their advice and education.Moore acknowledges the support of the US Science Support Program inthe USA for funding to participate in IODP Expeditions. We thank HessPetroleum Corporation for access to hydraulic modeling software. Na-than Bangs, anonymous reviewer, and Jin-Oh Park provided valuableeditorial assistance that substantially improved this manuscript.

References

Baba, T., Cummins, P.R., 2005. Contiguous rupture areas of the two Nankai Troughearthquake revealed by high-resolution tsunami waveform inversion. GeophysicalResearch Letters 32, L08305. http://dx.doi.org/10.1029/2004GL022320.

115J.C. Moore et al. / Tectonophysics 600 (2013) 108–115

Bangs, N., Moore, G., Gulick, S., Pangborn, E., Tobin, H., Kuromoto, S., Taira, A., 2009.Broad, weak regions of the Nankai Megathrust and implications for shallowcoseismic slip. Earth and Planetary Science Letters 284, 44–49.

Chang, C.D., et al., 2010. In situ stress state in the Nankai accretionary wedge estimatedfrom borehole wall failures. Geochemistry, Geophysics, Geosystems 11, Q0AD04.http://dx.doi.org/10.1029/2010GC003261.

Desbrandes, R., 1990. An overview of measurement while drilling-logging while dril-ling technology. In: Desbrandes, R. (Ed.), Measurement while Drilling. LouisianaState University, Louisiana State University, Baton Rouge, Louisiana, pp. 1–46.

Expedition 314 Scientists, 2009a. Expedition 314 methods. In: Kinoshita, M., Tobin, H.,Ashi, J., Kimura, G., Lallement, S., Screaton, E.J., Curewitz, D., Masago, H., Moe, K.T.,the Expedition 314/315/316 Scientists (Eds.), Proc. IODP, 314/315/316. IntegratedOcean Drilling Program Management International, Inc., Washington, DC. http://dx.doi.org/10.2204/iodp.proc.314315316.112.2009.

Expedition 314 Scientists, 2009b. Expedition 314 Site C0001. In: Kinoshita, M., Tobin, H.,Ashi, J., Kimura, G., Lallement, S., Screaton, E.J., Curewitz, D., Masago, H., Moe, K.T., theExpedition 314/315/316 Scientists (Eds.), Proc. IODP, 314/315/316. Integrated OceanDrilling Program Management International, Inc., Washington, DC. http://dx.doi.org/10.2204/iodp.proc.314315316.116.2009.

Expedition 314 Scientists, 2009c. Expedition 314 Site C0002. In: Kinoshita, M., Tobin, H.,Ashi, J., Kimura, G., Lallement, S., Screaton, E.J., Curewitz, D., Masago, H., Moe, K.T.,the Expedition 314/315/316 Scientists (Eds.), Proc. IODP, 314/315/316. IntegratedOcean Drilling Program Management International, Inc., Washington, DC. http://dx.doi.org/10.2204/iodp.proc.314315316.114.2009.

Expedition 314 Scientists, 2009d. Expedition 314 Site C0003. In: Kinoshita, M., Tobin, H.,Ashi, J., Kimura, G., Lallement, S., Screaton, E.J., Curewitz, D., Masago, H., Moe, K.T., theExpedition 314/315/316 Scientists (Eds.), Proc. IODP, 314/315/316. Integrated OceanDrilling Program Management International, Inc., Washington, DC. http://dx.doi.org/10.2204/iodp.proc.314315316.116.2009.

Expedition 314 Scientists, 2009e. Expedition 314 Site C0004. In: Kinoshita, M., Tobin, H.,Ashi, J., Kimura, G., Lallement, S., Screaton, E.J., Curewitz, D., Masago, H., Moe, K.T., theExpedition 314/315/316 Scientists (Eds.), Proc. IODP, 314/315/316. Integrated OceanDrilling Program Management International, Inc., Washington, DC. http://dx.doi.org/10.2204/iodp.proc.314315316.116.2009.

Expedition 314 Scientists, 2009f. Expedition 314 Site C0006. In: Kinoshita, M., Tobin, H.,Ashi, J., Kimura, G., Lallement, S., Screaton, E.J., Curewitz, D., Masago, H., Moe, K.T.,the Expedition 314/315/316 Scientists (Eds.), Proc. IODP, 314/315/316. IntegratedOcean Drilling Program Management International, Inc., Washington, DC. http://dx.doi.org/10.2204/iodp.proc.314315316.116.2009.

Expedition 315 Scientists, 2009a. Expedition 315 Site C0001. In: Kinoshita, M., Tobin,H., Ashi, J., Kimura, G., Lallement, S., Screaton, E.J., Curewitz, D., Masago, H., Moe,K.T., the Expedition 314/315/316 Scientists (Eds.), Proc. IODP, 314/315/316. Inte-grated Ocean Drilling Program Management International, Inc., Washington, DC.http://dx.doi.org/10.2204/iodp.proc.314315316.112.2009.

Expedition 315 Scientists, 2009b. Expedition 315 Site C0002. In: Kinoshita, M., Tobin,H., Ashi, J., Kimura, G., Lallement, S., Screaton, E.J., Curewitz, D., Masago, H., Moe,K.T., the Expedition 314/315/316 Scientists (Eds.), Proc. IODP, 314/315/316. Inte-grated Ocean Drilling Program Management International, Inc., Washington, DC.http://dx.doi.org/10.2204/iodp.proc.314315316.124.2009.

Expedition 316 Scientists, 2009a. Expedition 316 Site C0004. In: Kinoshita, M., Tobin,H., Ashi, J., Kimura, G., Lallemant, S., Screaton, E.J., Curewitz, D., Masago, H., Moe,K.T., the Expedition 314/315/316 Scientists (Eds.), Proc. IODP, 314/315/316. Inte-grated Ocean Drilling Program Management International, Inc., Washington, DC.http://dx.doi.org/10.2204/iodp.proc.314315316.133.2009.

Expedition 316 Scientists, 2009b. Expedition 316 Site C0006. In: Kinoshita, M., Tobin,H., Ashi, J., Kimura, G., Lallemant, S., Screaton, E.J., Curewitz, D., Masago, H., Moe,K.T., the Expedition 314/315/316 Scientists (Eds.), Proc. IODP, 314/315/316. Inte-grated Ocean Drilling Program Management International, Inc., Washington, DC.http://dx.doi.org/10.2204/iodp.proc.314315316.118.2009.

Expedition 332 Scientists, 2011. Site C0010. In: Kopf, A., Araki, E., Toczko, S., the Expedition332 Scientists (Eds.), Proc. IODP, 332. Integrated Ocean Drilling ProgramManagementInternational, Inc., Tokyo. http://dx.doi.org/10.2204/iodp.proc.332.103.2011.

Fyfe, W.S., Price, N.J., Thompson, A.B., 1978. Fluids in the earth's crust. Developments inGeochemistry, 1. Elsevier Scientific Publishing Co, New York (383 pp.).

Ingebritsen, S.E., Sanford, W.E., Neuzil, C.E., 2006. Groundwater in Geologic Processes.Cambridge University Press, New York (536 pp.).

Kinoshita, M., et al., 2009. Proc. IODP, 314/315/316. Integrated Ocean Drilling ProgramManagement International, Inc., Washington, DC. http://dx.doi.org/10.2204/iodp.proc.314315316.101.2009. (http://publications.iodp.org/proceedings/314_315_316/314315316toc.htm).

Miyazaki, S., Heki, K., 2001. Crustal velocity field of southwest Japan: subduction andarc-arc collision. Journal of Geophysical Research 106, 4305–4326.

Moore, G.F., et al., 2007. Three-dimensional splay fault geometry and implications fortsunami generation. Science 318, 1128–1131.

Moore, G.F., et al., 2009. Structural and seismic stratigraphic framework of theNanTroSEIZE Stage 1 transect1. In: Kinoshita, M., Tobin, H., Ashi, J., Kimura, G.,Lallement, S., Screaton, E.J., Curewitz, D., Masago, H., Moe, K.T., the Expedition 314/315/316 Scientists (Eds.), Proc. IODP, 314/315/316. Integrated Ocean Drilling Pro-gram Management International, Inc., Washington, DC.

Moore, J.C., Barrett, M., Moe, K.T., 2012. High fluid pressures and high fluid flow rates inthe megasplay Fault Zone, NanTroSEIZE Kumano Transect, SW Japan. Geochemistry,Geophysics, Geosystems 13 (1), Q0AD25. http://dx.doi.org/10.1029/2012GC004181.

Ostermeier, R.M., et al., 2000. Dealing with shallow-water flow in the deepwater Gulfof Mexico. Offshore Technology Conference, 11972. OTC, pp. 1–12.

Ostermeier, R.M., et al., 2002. Dealing with shallow-water flow in the deepwater Gulfof Mexico. The Leading Edge 21, 660–668.

Park, J.O., Tsuru, T., Kodaira, S., Cummins, P.R., Kaneda, Y., 2002. Splay fault branchingalong the Nankai subduction zone. Science 297, 1157–1160.

Park, J.H., Fujie, G., Wijerathne, L., Hori, T., Kodaira, S., Fukao, Y., Moore, G.F., Bangs, N.L.,Kuramoto, S., Taira, A., 2010. A low-velocity zone with weak reflectivity along theNankai subduction zone. Geology 38, 283–286.

Saito, S., Underwood, M.B., Kubo, Y., the Expedition 322 Scientists, 2010. NanTroSEIZEStage 2: subduction inputs. Proc. IODP, 322. Integrated Ocean Drilling ProgramManagement International, Inc., Tokyo. http://dx.doi.org/10.2204/iodp.proc.322.2010.(http://publications.iodp.org/proceedings/322/322toc.htm).

Seno, T., Stein, S., Gripp, A.E., 1993. A model for the motion of the Philippine Sea plateconsistent with NUVEL-1 and geological data. Journal of Geophysical Research 98,17,941–17,948.

Strasser, M., et al., 2009. Origin and evolution of a splay fault in the Nankai accretionarywedge. Nature Geoscience 2, 648–652.

Tobin, H., et al., 2009. NanTroSEIZE Stage 1 expeditiions: introduction and synthesis of keyresults. In: Kinoshita, M., Tobin, H., Ashi, J., Kimura, G., Lallemant, S., Screaton, E.J.,Curewitz, D., Masago, H., Moe, K.T., the Expedition 314/315/316 Scientists (Eds.),Proc. IODP, 314/315/316. Integrated Ocean Drilling ProgramManagement Internation-al, Inc., Washington, DC. http://dx.doi.org/10.2204/iodp.proc.314315316.101.2009.(http://publications.iodp.org/proceedings/314_315_316/314315316toc.htm).

Underwood, M.B., Moore, G.F., 2012. Evolution of sedimentary environments in thesubduction zone of southwest Japan: recent results from the NanTroSEIZE Kumanotransect. In: Busby, C., Azor, A. (Eds.), Tectonics of Sedimentary Basins: RecentAdvances. Blackwell Publishing Ltd., New York, pp. 310–326.

Ward, C., Andreassen, E., 2000. Pressure-while-drilling data improve reservoir drillingperformance. SPE Drilling and Completion 13 (1), 19–24.

Zang, S.X., Chen, Q.Y., Ning, J.Y., Shen, Z.K., Liu, Y.G., 2002. Motion of the Philippine Seaplate consistent with the NUVEL-1A model. Geophysical Journal International 150,809–819.