mantle, the nature of the continent-ocean transition zones, plate interactions, and neotectonics in the Arctic.

The broad-band stations should be sited to create favorable source-receiver paths for surface wave and tomographic inversions across the Arctic Ocean Basin. Existing seismic stations with long operating histories should be upgraded and ice stations should operate seismographs where feasible. The broad-band stations should be supplemented with local networks in areas of tectonically significant seismicity such as northeastern Alaska, the Mackenzie Delta, and the southwestern Canadian Arctic Islands. Such local networks provided important supplementary data in northern Alaska and the Canadian Arctic from 1975 to 1982.

A primary objective of seismological research in the Arctic Ocean Basin is to determine the structure of the crust and upper mantle beneath the basins, ridges, and continental margins of the Amerasia Basin. Tomographic inversion of surface-wave phase velocities can provide information on the structure of the crust and upper mantle at wavelengths of 100 km or less with resolution in depth of 10 km (Yu and Mitchell, 1979). Because regional body wave phases are also well excited along most earthquake paths that cross the Arctic Ocean, three-dimensional elastic and anelastic modeling of these phases would provide insights into the structure beneath the large bathymetric features of the Arctic Ocean Basin, information that would be especially useful when interpreted in conjunction with improved potential field and long-offset seismic refraction data. Reflected body wave phases could also be used to constrain further the elastic and anelastic parameters of near-surface features. The present paucity of high-quality seismograph stations in the Arctic, particularly in the Soviet sector, limits the number of ray paths that can be studied. The lack of stations on arctic continental margins also makes it difficult to separate the contributions of ocean and continental crust to the dispersion curves. High-quality stations can also serve as anchors for regional arrays, similar to those envisioned by PASCAL, which can better constrain near-source and near-station structure through the calculation of source and receiver functions. High-priority targets for seismic crustal structure studies include the Chukchi Borderland, Mendeleev Ridge, the Canada Plain, and the East Siberian and Barents Shelves. Improved earth structure models would also enhance moment tensor inversion and other source process studies. Further, more numerous and improved seismograph stations, possibly including ocean-bottom seismometers, would aid in the study of ocean-floor anisotropy and the details of regional surface wave dispersion.

Some segments of the arctic continental margin display high seismic activity. Along the Canadian Arctic Islands, for example, clusters of earthquakes with magnitudes approaching 6 are associated with positive gravity anomalies. Both sediment loading (Hasegawa et al., 1979) and deglaciation stresses (Stein et al., 1979) have been proposed as causative factors. More precise location of the low-to moderate-magnitude events would provide significant insight into the structural character and geodynamics of these margins.

It is curious that earthquake clusters with events as large as magnitude 7 lie landward of the continental slope near some aseismic arctic continental margins. These clusters occur within continental shelf basins or along subbasin structures, and their study may provide important insights into the development of structurally controlled sedimentary basins within passive continental margins.

Delineation of microseismicity and transform faults along the Arctic Mid-Ocean Ridge and its junction with the Laptev Shelf and identification of volcanic earthquakes along the ridge axis would provide important insights into the mechanisms that operate at slow-spreading mid-ocean

Front Matter (R1-R12)

Executive Summary (1-4)

1 Introduction (5-6)

2 Physiography (7-8)

3 Role of the Arctic in Global Solid-Earth Geoscience (9-13)

4 Rationale for Focusing on the Arctic Ocean Basin and Its Margins (14-18)

5 The Next Stage of Arctic Solid-Earth Geoscience Research (19-45)

6 Logistic Realities and Opportunities (46-55)

7 Research Priorities (56-58)

8 Special Concerns (59-60)

References (61-67)