50˚
50˚
E
E
NC
ILL VI
NV PRO
E
R
EN
G
45˚
N
LA
C
H
IA
40˚
AP
PA
40˚
EA
O
AM
N
R
O
G
45˚
35˚
New England
Seamounts
35˚
Bermuda
Continental Slope
30˚
-80˚
-75˚
-300
-200
-100
-60˚-80˚
-65˚
-70˚
-75˚
-65˚
-70˚
30˚
-60˚
+100 +200 +300
shear velocity perturbation, m/s
46˚
-75
100 km
45˚
45˚
44˚
44˚
43˚
43˚
42˚
42˚
NW
-100
depth, km
100 km
-125
SE
4.25
4.3
46˚
4.3
5
4.4
4.4
5
-150
-175
-200
-76
41˚
-75
-74
-76˚
-74˚
-72˚
-70˚ -76˚
-74˚
-72˚
4.35
4.40
4.45
4.50
4.55
4.20 4.25 4.30 4.35 4.40 4.45
velocity, km/s
-72
-71
-70
-70˚
4.00
-73
longitude, deg
41˚
4.20
4.30
4.75
velocity, km/s
Figure 1. UPPER LEFT Shear wave velocity anomalies 100 km beneath the eastern North America passive margin (adapted
from Van der Lee and Nolet, 1997). UPPER RIGHT: Tectonic units of the eastern North America passive margin. A depth
contour of 2000m (shaded) outlines the edge of the continent. AM - Adirondack Mountains.
LOWER PANEL Regional variations in shear wave speed at 150 km depth, as imaged by body wave tomography with S and
SKS waves (Levin et al., 1999) (left) and Raleigh wave tomography (Van der Lee and Nolet, 1997) (middle). Solid line on the
middle panel indicates the trace of the crossection shown at right. There is a general aggreement in the trend of the low
velocity features despite large differences in sampling and vastly disparate scales of these studies (body waves - the region
shown, Rayleigh waves - continent-wide). Note an "uplift" of velocity contours towards the interior of the craton.