RECENT, TECTONICALLY INDUCED, SURFICIAL STRESS-RELIEF STRUCTURES IN THE OTTAWA HULL AREA, CANADA

Contemporary reverse faults, marked by offset boreholes, were identifi ed in two roadcuts, and recently formed pop-ups, which are surficial c hevron folds, have been recognized in a quarry in the Ottawa-Hull area of Ontario and Quebec, Canada. Displacement directions of the hanging walls, marked by the offset boreholes, are commonly north-northeast t o east-northeast, though one set shows displacement to the northwest. The pop-ups recorded during this investigation show average orientatio ns of 120 and 063 degrees. These are similar to the average trends of 136 and 074 degrees documented in a previous study from a quarry about 20 km away. East-southeast- to southeast-trending pop-ups predominate in the two quarries and are kinematically compatible with most of the offset borehole directions recognized to date in the Ottawa-Hull area . Moreover, the quarry-floor pop-up trends in the Ottawa-Hull area are consistent with those of open field, lake bottom and other quarry-flo or pop-ups in an area extending from the Miramichi region of New Bruns wick into the east-central U.S.A. The compressional origin of the reve rse faults and pop-ups, and the predominant orientations of those stru ctures, are compatible with the current ambient stress field in easter n North America. This implies that both the displaced boreholes and qu arry-floor pop-ups are products of that stress field, and, despite the ir presence in excavations, are tectonic in origin.