A Refraction Seismic Survey of Martinique Beach: Geometry and Significance to Barrier Beach Evolution

Abstract

During the summer of 1984 a refraction seismic survey was conducted at Martinique Beach using a 12 geophone array and seismic recorder with a hammer plate as the acoustic source. Sixteen sites were occupied along the 3.5 km beach with geophone sounding lines varying in length from 15m to 50m in order to examine the stratigraphy and depth of the bedrock. Current theories based upon nearshore marine seismic reflection profiles and coastal barrier coring indicate that barrier beaches on the Eastern Shore of Nova Scotia such as Martinique Beach, exist at the mouth of Pleistocene channels. These channels resulted from scouring of till and the Meguma Group acoustic basement by glacial ice and meltwater. To date, no seismic measurements on beaches have been made to extend nearshore data shoreward. The present survey was designed to determine whether significant variability in sediment thickness, indicating a bedrock channel, exists at Martinique Beach. From each of the sites, the sound velocity data were analyzed to determine depth to the boundary between unconsolidated sediments and the acoustic basement. Quantitative results presented in this thesis indicate that from Whale Point to the mid-beach outcrop the average bedrock depth is approximately 15m. From the midbeach outcrop to Flying Point further east, however, results indicate a 20m deep bedrock channel of less than 0.5 km in width. Such a relatively narrow, deep channel provides strong speculative evidence for differential erosion as a result of glacial processes and is consistent with current theories of the location of beaches such as Martinique.

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