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Fault rock assemblages reflect interaction between deformation, stress, temperature, fluid, and chemical regimes on distinct spatial and temporal scales at various positions in the crust. Here we interpret measurements made in the hanging‐wall of the Alpine Fault during the second stage of the Deep Fault Drilling Project (DFDP‐2). We present observational evidence for extensive fracturing and high hanging‐wall hydraulic conductivity (∼10−9 to 10−7 m/s, corresponding to permeability of ∼10−16 to 10−14 m2) extending several hundred meters from the fault's principal slip zone. Mud losses, gas chemistry anomalies, and petrophysical data indicate that a subset of fractures intersected by the borehole are capable of transmitting fluid volumes of several cubic meters on time scales of hours. DFDP‐2 observations and other data suggest that this hydrogeologically active portion of the fault zone in the hanging‐wall is several kilometers wide in the uppermost crust. This finding is consistent with numerical models of earthquake rupture and off‐fault damage. We conclude that the mechanically and hydrogeologically active part of the Alpine Fault is a more dynamic and extensive feature than commonly described in models based on exhumed faults. We propose that the hydrogeologically active damage zone of the Alpine Fault and other large active faults in areas of high topographic relief can be subdivided into an inner zone in which damage is controlled principally by earthquake rupture processes and an outer zone in which damage reflects coseismic shaking, strain accumulation and release on interseismic timescales, and inherited fracturing related to exhumation.

We conducted palaeoseismic studies along the North Anatolian fault both east and west of the Marmara Sea to evaluate its recent surface rupture history in relation to the well-documented historical record of earthquakes in the region, and to assess the hazard of this major fault to the city of Istanbul, one of the largest cities in the Middle East. Across the 1912 rupture of the Ganos strand of the North Anatolian fault west of the Marmara Sea, we excavated 26 trenches to resolve slip and constrain the earthquake history on a channel-fan complex that crosses the fault at a high angle. A distinctive, well-sorted fine sand channel that served as a marker unit was exposed in 21 trenches totaling over 300 m in length. Isopach mapping shows that the sand is channelized north of the fault, and flowed as an overflow fan complex across a broad fault scarp to the south. Realignment of the feeder channel thalweg to the fan apex required about 9+1 m of reconstruction. Study of the rupture history in several exposures demonstrates that this displacement occurred as two large events. Analysis of radiocarbon dates places the age of the sand channel as post AD 1655, so we attribute the two surface ruptures to the large regional earthquakes of 1766 and 1912. If each was similar in size, then about 4 -5 m of slip can be attributed to each event, consistent with that reported for 1912 farther east. We also found evidence for two additional surface ruptures after about AD 900, which probably correspond to the large regional earthquakes of 1063 and 1344 (or 1354). These observations suggest fairly periodic occurrence of large earthquakes (RI ¼ c. 283+113 years) for the past millennium, and a rate of c. 16 mm/a if all events experienced similar slip.We excavated six trenches at two sites along the 1999 Izmit rupture to study the past earthquake history along that segment of the North Anatolian fault. One site, located in the township of Köseköy east of Izmit, revealed evidence for three surface ruptures (including 1999) during the past 400 years. The other trench was sited in an Ottoman canal that was excavated (but never completed) in 1591. There is evidence for three large surface rupturing events in the upper 2 m of alluvial fill within the canal at that site, located only a few kilometres from the Köseköy site.

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[1] We analyze progressively displaced late Quaternary (<12 ka) fluvial terraces along the Wellington fault, near Wellington, New Zealand. Optically stimulated luminescence dating indicates that degradational terraces were produced at a rate of about one terrace per 1000 years, similar to the rate of earthquake surface rupturing. Along the Hutt River near Te Marua, we measured the strike slip of 15 terrace risers and paleochannels on the lowest 8 of these terraces, of Holocene age. The river, after earthquakes, was generally capable of smoothing its faulted riverbanks. The dextral offsets appear to fall into several groupings that record slip accumulation during the last four earthquakes. We calculate a mean single-event slip of 5.0 ± 0.24 m (95% confidence) with an RMS scatter (1s) of slips about the mean of ±1.5 m. The coefficient of variation (CV) of single-event slip is thus 0.30. This CV is slightly less than a recently compiled global average for point measurements on strike-slip faults, suggesting that the southernmost Wellington fault has behaved in a more nearly characteristic way. We speculate that recent large earthquake ruptures have been bounded on their southern end by the Wellington fault's offshore fault termination and perhaps on their northern end by a ∼2 km wide releasing step over. Such persistent sources of rupture arrest might have led to a relative uniformity of rupture dimensions and slip amounts. We infer a late Holocene dextral slip rate of ≥4.5 ± 0.4 mm/yr (1s) and <8.2 mm/yr, and a mean earthquake recurrence interval of ∼610-1100 years.

We combine recently acquired airborne light detection and ranging (LiDAR) data along a portion of the Alpine fault with previous work to defi ne the ways in which the plate-boundary structures partition at three different scales from <10 6 to 10 0 m. At the fi rst order (<10 6-10 4 m), the Alpine fault is a remarkably straight and unpartitioned structure controlled by inherited and active weakening processes at depth. At the second order (10 4-10 3 m), motion is serially partitioned in the upper ~1-2 km onto oblique-thrust and strike-slip fault segments that arise at the scale of major river valleys due to stress perturbations from hanging-wall topographic variations and river incision destabilization of the hanging-wall critical wedge, concepts proposed by previous workers. The resolution of the LiDAR data refi nes second-order mapping and reveals for the fi rst time that at a third order (10 3-10 0 m), the fault is parallel-partitioned into asymmetric positive fl ower structures, or fault wedges, in the hanging wall. These fault wedges are bounded by dextral-normal and dextral-thrust faults rooted at shallow depths (<600 m) on a planar, moderately southeast-dipping, dextral-reverse fault plane. The fault wedges have widths of ~300 m and are bounded by and contain kinematically stable fault traces that defi ne a surface-rupture hazard zone. Newly discovered anticlinal ridges between fault traces indicate that a component of shallow shortening within the fault wedge is accommodated through folding. A fault kinematic analysis predicts the fault trace orientations observed and indicates that third-order fault trace locations and kinematics arise independently of topographic controls. We constructed a slip stability analysis that suggests the new strike-slip faults will easily accommodate displacement within the hanging-wall wedge, and that thrust motion is most easily accommodated on faults oblique to the overall strike of the Alpine fault. We suggest that the thickness of footwall sediments and width of the fault damage zone (i.e., presence of weaker, more isotropic materials) are major factors in defi ning the width, extent, and geometry of third-order near-surface fault wedges.