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The Neogene section in the northern Taranaki Basin, offshore New Zealand, displays an interaction among prograding clinoforms, listric growth faults formed at the base of slope and mass transport deposits that fill the growth fault depocentres. This study focuses on one of these systems, the Karewa Fault and mass transport deposit (MTD), in order to understand the genetic relationship between the fault and the MTD in its hangingwall depocentre, i.e. did the MTD fill existing accommodation space? Did the MTD trigger growth fault displacement? Or is there some other relationship? Most mass transport deposits are elongate in the transport direction and exhibit a length:width aspect ratio of more than 1. However, the 90 km 2 Karewa Fault MTD is at least three times wider than it is long, which is atypical for MTDs reported in the literature, where~80% have a length: width ratio >1. The transport direction of the MTD is to the WNW, as indicated by the location and internal structure of the compressional toe and the headwall scarp region of the Karewa Fault. The structural and sequence geometries on seismic reflection data indicate the MTD formed during the late stage of growth fault activity, and locally truncates the upper part of the Karewa Fault. The MTD is inferred to have originated by local destabilization of the sediment package overlying the Karewa Fault related to the escape of overpressured fluids along the fault. The resulting MTD was translated locally by only a few kilometres. This unusual cause for an MTD also resulted in its atypical length-width-thickness aspect ratios.

The Cenozoic Phitsanulok rift basin (Thailand) is extensively affected by igneous intrusions and lava flows. In the Ruang Thong-Sai Ngam area, the E-A01 well drilled the early Miocene synrift Lan Krabu Formation, and unexpectedly encountered a 300-m-thick olivine dolerite sill (sill 3). The top and base of the sill are characterized by medium-to low-amplitude contrasts, atypical for most (high amplitude) responses from intrusions. Seismic interpretation, artificial neural networks, and model-based inversion were used to understand the seismic response of the intrusions. Two key factors combined to mask sill 3: (1) stacking of common depth point gathers resulted in lower amplitudes at the top and base of the sill, and (2) multiple intruded sills separated by thin shales caused internal reflectivity. Using the sill geometries, sill stratigraphic position, and inferred magma flow directions from broken bridges, an estimate of the relative timing of the sills, and the local stress orientations at the time of displacement was made. Three sills are inferred to have been emplaced during the Miocene when the maximum horizontal stress direction (Shmax) was north-south and two were emplaced during the Miocene when the stress direction was approximately east-west. Such orientations are compatible with known phases of Miocene inversion (east-west Shmax) and extension (northsouth Shmax), although local stress changes associated with igneous bodies could also explain rotation to an east-west Shmax.

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