5. Site 1073

Site 1073 constitutes one of four second-priority sites approved for drilling that were to be undertaken in the event that either time allowed or that operations had to be curtailed at both primary shelf sites. With 5 days remaining on Leg 174A, the decision was made to move to the slope, because it seemed unlikely that at Sites 1071 and 1072 it would be possible to reach objectives deeper than surface m1(s) without unreasonable risk of equipment loss because of unstable hole conditions. Site 1073 was designed to drill as deeply as time would allow into “Icehouse” sediments (Oligocene and younger) at a location where the physical stratigraphy could be related to sequence boundaries traced seaward from the shelf. The objective at Site 1073 is to provide the age and deep-water facies control for surfaces that in shallow water can yield paleobathymetry and facies characterization relevant to determining the history and geologic impact of glacial-eustatic change

3. Site 1071

Site 1071 is one of two sites approved for JOIDES Resolution drilling on the New Jersey continental shelf; these sites form part of a transect of holes from the slope (ODP Leg 150) to coastal outcrops (150X and 174AX) that constitute the Mid-Atlantic Sea-level Transect. The primary goals of the transect are (1) to date sequence boundaries of Oligocene to Holocene age and compare this stratigraphic record with the timing of glacial-eustatic changes inferred from deep-sea d18O variations; (2) to place constraints on the amplitudes and rates of sea-level change that may have been responsible for unconformity development; (3) to assess the relationships between depositional facies and sequence architecture; and (4) to provide a baseline for future scientific ocean drilling that will address the effects and timing of sea-level changes on this and other passive margins. Site 1071 provides information primarily about late middle Miocene and younger sequences at locations landward of their respective rollovers/breakpoints, the positions at which each sequence boundary steepens seaward into a clinoform

4. Site 1072

Site 1072 is the second of two sites approved for JOIDES Resolution drilling on the New Jersey continental shelf; together with Site 1071, it forms part of a transect of holes from the slope (Ocean Drilling Program [ODP] Leg 150) to coastal outcrops (Legs 150X and 174AX) that constitute the Mid-Atlantic Sea-level Transect. The primary goals of the transect are to: (1) date sequence boundaries of Oligocene to Holocene age and compare this stratigraphic record with the timing of glacial eustatic changes inferred from deep-sea d18O variations; (2) place constraints on the amplitudes and rates of sea-level change that may have been responsible for unconformity development; (3) assess the relationships between depositional facies and sequence architecture; and (4) provide a baseline for future scientific ocean drilling that will address the effects and timing of sea-level changes on this and other passive margins. Site 1072 is ~3.5 km seaward of Site 1071 and coincides with the rollover or breakpoint in sequence boundary m0.5(s). This site provides information primarily about upper Miocene and younger strata and permits a comparison, in the direction of progradation, with the succession at Site 1071

The thickness of subduction plate boundary faults from the seafloor into the seismogenic zone

The thickness of an active plate boundary fault is an important parameter for understanding the strength and spatial heterogeneity of fault behavior. We have compiled direct measurements of the thickness of subduction thrust faults from active and ancient examples observed by ocean drilling and fi eld studies in accretionary wedges. We describe a general geometric model for subduction thrust décollements, which includes multiple simultaneously active, anastomosing fault strands tens of meters thick. The total thickness encompassing all simultaneously active strands increases to ~100–350 m at ~1–2 km below seafl oor, and this thickness is maintained down to a depth of ~15 km. Thin sharp faults representing earthquake slip surfaces or other discrete slip events are found within and along the edges of the tens-ofmeters- thick fault strands. Although fl attening, primary inherited chaotic fabrics, and fault migration through subducting sediments or the frontal prism may build mélange sections that are much thicker (to several kilometers), this thickness does not describe the active fault at any depth. These observations suggest that models should treat the subduction thrust plate boundary fault as <1–20 cm thick during earthquakes, with a concentration of postseismic and interseismic creep in single to several strands 5–35 m thick, with lesser distributed interseismic deformation in stratally disrupted rocks surrounding the fault strands