A STUDY OF THE DISTRIBUTION, THICKNESS AND ELASTIC MODULI OF THE MASSENA CLAY, ST. LAWRENCE COUNTY, NEW YORK

The Massena, New York area, located along the St. Lawrence River in northern New York, is the site of significant seismic activity including the most damaging earthquake in New York State. On September 5, 1944, an earthquake Intensity VIII occurred in the Massena area which destroyed 90% of the chimneys and did extensive damage to schools and other buildings. The historic earthquake data in the area is persistent over a 400 year period and it is likely that another damaging earthquake could occur in the area. Subsurface surveys and surficial geologic studies indicate primarily three types of deposits of different characteristics; glacial till and outwash and a clay known as the Massena or Leda Clay. Practically all damage by the Massena-Cornwall earthquake was to buildings constructed on the Massena Clay. However, there is no certainty that structures founded on deposits other than clay will be immune to damage.

The purpose of this study is to compile all available information about the distribution of the clay and determine seismic wave propagation velocities of it in selected areas. Three areas were selected for wave propagation studies: Snell Lock, an area long Route 37 where the clay outcrops, and an area near Massena Center where a major landslide occurred. Seismic refraction surveys were conducted with a StrataView exploration seismograph to map the subsurface geology and determine the P and S wave velocities in these areas. A wooden plank with a weight superimposed and horizontal geophones were used to generate and detect the S waves. These velocities and the densities are used to calculate the dynamic elastic moduli of the Massena Clay. The dynamic elastic moduli of the Massena Clay are related to its response to earthquake vibrations. This relationship could help us better understand why the clay fails during earthquakes. The study could help us understand the seismic hazard potential posed by the Massena Clay in the Massena area.