Numerical simulation of fracturing in concrete structures using a combination of smeared and discrete approaches

Abstract

Nearly all of the rivers draining the Manhattan Prong physiographic subprovince in New York City and vicinity flow southwestward in wide NE-SW-trending strike-valley lowlands underlain by the Cambro-Ordovician Inwood Marble. For most of its course, the Bronx River flows in such a strike-valley lowland. However, just at the point where the NW-SE-trending Mosholu fault offsets this marble lowland, the Bronx River leaves the lowland and flows southward across the more-resistant gneisses and schists of the Hartland Formation in the narrow N-S-trending Snuff Mill gorge. Schuberth 1968 advocated that the Bronx River started to erode the Snuff Mill gorge in Miocene time (15 million years ago) by finding a weak zone in the schist along a N-S-trending fault. By contrast, Kemp 1897 made a convincing case for a postglacial age (possibly 13,000 years ago) for the Bronx River's diversion into the Snuff Mill gorge. Subsurface data demonstrate that valley-fill sediments NE of the point of diversion include a clay overlying a probable till. We infer that this clay was deposited in a lake which formed when the Bronx River's former path to the SW was blocked. We infer that the mechanism of blockage was neotectonic uplift of the East 204th Street bulge, a bedrock barrier situated on the footwall block of the NW-trending, oblique-slip Mosholu fault at the exact point where the Bronx River was diverted. Given the history of time-separated seismic activity in New York City, the possibility that a damaging earthquake will affect this densely populated area should not be ruled out.