S U M M A R YA global palaeointensity data base was constructed from all published data from volcanic rocks in geological time older than 0.03 Ma. The data base contains a total of 1123 flow mean data retrieved from 83 original papers. Various features of the Earth's dipole moment were examined from the data which are based on Thellier and Shaw methods. Long-term variation of the Earth's dipole moment seems to have existed in the past 300 Ma with a broad minimum at 120-180 Ma as suggested by Prevot et af. (1990). However, due to limited site distribution we cannot regard this Mesozoic dipole low as being completely established. Precambrian palaeointensity data are still insufficient to conclude any long-term variation in this time range, although the geodynamo processes of moderate magnitude definitely existed in the early time of the Earth's history. The xz test was applied to the distribution of the virtual dipole moment for the past 5 M a in which the transitional data were excluded; the results indicate that the distribution of virtual dipole moment is better represented by a log-normal distribution rather than a normal distribution, and this tendency seems to be true for the past 20 Ma. The relation of mean palaeointensity versus palaeomagnetic colatitude was examined for the past 10Ma for the data excluding transitions. The relation is concordant with a theoretical curve from a geocentric axial dipole. This reconfirms that the dipole field was dominant in the past geomagnetic field, which is the dipole hypothesis in palaeomagnetism. On the other hand, the virtual dipole moment is much smaller for transitional palaeomagnetic fields, and a virtual geomagnetic pole lower than 45" seems to be a reasonable criterion to be categorized as a transition. The mean dipole moment for the pole latitude of 30"N-50°N band is larger than that for 3O0S-50"S, indicating that there might have been a persistent asymmetry of palaeointensity between normal and reversed states, or some kind of geometrical asymmetry between the Northern and Southern Hemispheres.

Expedition 344 summaryProc. IODP | Volume 344 2 from velocity-strengthening to velocity-weakening friction, and shear becomes localized. The onset of seismogenic behavior is correlated with the intersection of the 100°-150°C isotherm and the subduction thrust (Hyndman et al., 1997;Oleskevich et al., 1999). With increasing depth down the subduction thrust, the frictional characteristics undergo a second transition either due to the juxtaposition with the forearc mantle or because the rocks are heated to 350°-450°C and can no longer store elastic stresses needed for rupture. Transitional regions between the three zones have conditional stability and can host rupture but are generally not thought to be regions where large earthquakes initiate.Although this three-zone two-dimensional view of the subduction thrust provides a reasonable framework, it is simplistic. Rupture models for large subduction earthquakes suggest significant fault plane heterogeneity in slip and moment release that in three dimensions is characterized as patchiness (Bilek and Lay, 2002). Additionally, we now know the transition zone from stable to unstable sliding is not simple but hosts a range of fault behaviors that includes creep events, strain transients, slow and silent earthquakes, and low-frequency earthquakes (Peng and Gomberg, 2010;Beroza and Ide, 2011;Ide, 2012).Fundamentally unknown are the processes that change fault behavior from stable sliding to stick-slip behavior. Understanding these processes is important for understanding earthquakes, the mechanics of slip, and rupture dynamics. For a fault to undergo unstable slip, fault rocks must have the ability to store elastic strain, be velocity weakening, and have sufficient stiffness. Hypotheses for mechanisms leading to the transition between stable and unstable slip invoke temperature, pressure, and strain-activated processes that lead to downdip changes in the mechanical properties of rocks. These transitions are also sensitive to fault zone composition, lithology, fabric, and fluid pressures.The composition of the material in the fault zone and its contrast with the surrounding wall rock play a key role in rock frictional behavior. The frictional state of the incoming sediment changes progressively with increasing temperature and pressure as it travels downdip. Important lithologic factors influencing friction are composition, fabric, texture, and cementation of rocks, as well as fluid pore pressure (Bernabé et al., 1992;Moore and Saffer, 2001;Beeler, 2007;Marone and Saffer, 2007;Collettini et al., 2009). For example, fault rocks with high phyllosilicate content are generally weaker than rocks with low phyllosilicate content (Ikari et al., 2011). Sediment properties including porosity, permeability, consolidation state, and alteration history also exert a strong influence on fault zone behavior. At erosive margins, where the plate boundary cuts into the overriding plate, the composition and strength of the upper plate is also important (McCaffrey, 1993).Field observations and la...

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Drilling operationsThe advanced piston corer (APC), extended core barrel (XCB), and rotary core barrel (RCB) systems were used during Expedition 344. The APC and XCB systems were used to recover the sedimentary section in Holes U1381C, U1412A, U1412B, U1413A, U1413B, and U1414A and the sediment/basement interface at Hole U1381C. The RCB system was used to recover sediment and basement sections in Holes U1380C, U1412C, U1412D, U1413C, and U1414A.The APC system cuts soft-sediment cores with minimal coring disturbance relative to other IODP coring systems. After the APC core barrel is lowered through the drill pipe and lands above the bit, the drill pipe is pressured up until the two shear pins that hold the inner barrel attached to the outer barrel fail. The inner

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