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12.7.2 Geophysical Investigations in the Cascadia Subduction Zone
Figure 12.41 presents a schematic map of the Cascadia subduction zone, reflecting
the main features of contemporary tectonic processes: crustal seismicity, volcanism,
and formation of the accretionary complex.
Earthquake sources concentrate in the northern and southern parts of the sub-
duction zone, within the states of Washington and California, where the Benioff
zone is traced quite reliably. According to seismological evidence, the oceanic plate
subducts at a low angle in these areas, with its dip gradually increasing to 45
◦
.At
the same time, the central part of the subduction relating to the state of Oregon is
aseismic. Here, the oceanic plate also starts subducting at a low angle, but seismic
tomography data indicate that, at depths of about 40-80 km, it is sharply curved and
then descends at an angle of about 70
◦
.
Fig. 12.41
Evidences of recent tectonic processes: (1) accretionary complex, (2) crustal seismicity,
(3) Quaternary volcanic rocks, (4) depth to the Benioff zone in km (Romanyuk et al., 2001b)
