[1] The transpressional boundary between the Australian and Pacific plates in the central South Island of New Zealand comprises the Alpine Fault and a broad region of distributed strain concentrated in the Southern Alps but encompassing regions further to the east, including the northwest Canterbury Plains. Low to moderate levels of seismicity (e.g., 2 > M 5 events since 1974 and 2 > M 4.0 in 2009) and Holocene sediments offset or disrupted along rare exposed active fault segments are evidence for ongoing tectonism in the northwest plains, the surface topography of which is remarkably flat and even. Because the geology underlying the late Quaternary alluvial fan deposits that carpet most of the plains is not established, the detailed tectonic evolution of this region and the potential for larger earthquakes is only poorly understood. To address these issues, we have processed and interpreted high-resolution (2.5 m subsurface sampling interval) seismic data acquired along lines strategically located relative to extensive rock exposures to the north, west, and southwest and rare exposures to the east. Geological information provided by these rock exposures offer important constraints on the interpretation of the seismic data. The processed seismic reflection sections image a variably thick layer of generally undisturbed younger (i.e., < 24 ka) Quaternary alluvial sediments unconformably overlying an older (>59 ka) Quaternary sedimentary sequence that shows evidence of moderate faulting and folding during and subsequent to deposition. These Quaternary units are in unconformable contact with Late Cretaceous-Tertiary interbedded sedimentary and volcanic rocks that are highly faulted, folded, and tilted. The lowest imaged unit is largely reflection-free PermianTriassic basement rocks. Quaternary-age deformation has affected all the rocks underlying the younger alluvial sediments, and there is evidence for ongoing deformation. Eight primary and numerous secondary faults as well as a major anticlinal fold are revealed on the seismic sections. Folded sedimentary and volcanic units are observed in the hanging walls and footwalls of most faults. Five of the primary faults represent plausible extensions of mapped faults, three of which are active. The major anticlinal fold is the probable continuation of known active structure. A magnitude 7.1 earthquake occurred on 4 September 2010 near the southeastern edge of our study area. This predominantly right-lateral strike-slip event and numerous aftershocks (ten with magnitudes ≥5 within one week of the main event) highlight the primary message of our paper: that the generally flat and topographically featureless Canterbury Plains is underlain by a network of active faults that have the potential to generate significant earthquakes.

Nearly 270 km of crustal seismic reflection data obtained by Lithoprobe in the southern Canadian Cordillera provide a geometric link between the Rocky Mountain foreland thrust and fold belt, the Purcell anticlinorium, and the extensional regime superimposed on the crystalline core zone. Autochthonous North American basement and its overlying deformed and transported cover can be traced from the thrust and fold belt, beneath the Rocky Mountain trench, to 20 km depth beneath the central part of the Purcell anticlinorium. The Purcell anticlinorium is cored by foreshortened Proterozoic supracrustal rocks that were carried northeastward on a series of west dipping imbricate thrust faults. These faults crop out within and east of the anticlinorium and converge downward with subhorizontal detachments above the autochthonous North American basement. Beneath the western Purcell anticlinorium and Kootenay Arc, reflections associated with the Purcell stratigraphy and its underlying crystalline basement terminate at about 20 km depth and may be truncated against the east dipping Eocene Slocan Lake fault zone. The Slocan Lake fault zone is clearly imaged from the surface to about 12 km depth and can probably be followed discontinuously to about 25 km depth. A west‐dipping, high amplitude reflection from beneath the Valhalla gneiss complex outlines the domal geometry of the complex and is probably related to an east verging compressional shear zone.