P-wave travel-time residuals in the Newfoundland Appalachians

Abstract

Teleseisms and quarry blasts were recorded at 24 temporary seismograph sites along a line across the northern Dunnage Zone of Newfoundland. Azimuthally dependent functions were also determined for teleseismic P-wave travel-time residuals at the permanent St. John's (STJ) and Corner Brook (CBK) seismographs. In order to minimize the effects of reading errors and structure far from the receivers, absolute residuals at the field sites were then obtained by correlating the records with those from STJ and CBK and using the residual functions for these two stations. The P-wave residuals in north-central Newfoundland tend to be up to half a second later than at STJ and CBK, with the more positive values towards the east of the region. The direction of fastest approach for rays varies from southeast at STJ to southwest towards the western side of the Dunnage Zone. The travel-time residuals are generally similar to variations observed elsewhere in the Appalachians.The residuals and gravity data indicate that the crust is about 40 km thick over most of the Dunnage Zone, possibly increasing by several kilometres under the Gander Zone and western Avalon Platform, which could be consistent with a former subduction zone in the region. The low crustal velocity of 6.2 km s−1 may support an allochthonous model for central Newfoundland, with average crustal thickening of about 10 km compared with adjacent platform areas.