Overview of Offshore-Onshore Wide-Angle Seismic Recordings in the Bering-Chukchi Sea

T M Brocher (U.S. Geological Survey, 345 Middlefield Rd., MS 977, Menlo Park, CA 94025; tel. 415-329-4737; e-mail: brocher@andreas.wr.usgs.gov) R M Allen (Dept. Geol. Sci., Univ. Durham, Durham, DH1 3LE, UK) D B Stone (Geophys. Inst., Univ. Alaska, Fairbanks, AK 99775) L W Wolf (Dept. Geol., Auburn Univ., Auburn, AL 36849) S L Klemperer and B K Galloway (Dept. Geophys., Stanford Univ., Stanford, CA 94305)



Abstract submitted to AGU Fall Meeting, December 1995.

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The U.S. Geological Survey (USGS) and University of Alaska, Fairbanks (UAF), deployed an array of twelve 3-component REFTEK and PDAS recorders which recorded air gun signals during both the northbound and southbound legs of the R/V Ewing. Fourteen two-sided wide-angle seismic reflection/refraction profiles were recorded in western Alaska and eastern Siberia. Data quality obtained during the experiment is highly variable, depending primarily on the sea state and wind speed conditions. The two regions having the more dense wide-angle coverage lie (1) in the Chukchi Sea between Point Hope and Point Lay and (2) south of the Bering Straits in a triangular region between the northwestern tip of St. Lawrence Island, Provideniya, in eastern Siberia, and Tin City, on the Seward Peninsula. Upper mantle refractions, Pn, generated by the air gun signals were observed to ranges in excess of 400 km, and upper crustal refractions, Pg, can be traced to offsets in excess of 300 km. Lower crustal reflections observed in the wide-angle data correlate well in location and time with those observed on the vertical-incidence multichannel reflection data. One-dimensional forward modeling of the refracted and reflected arrivals indicates that the crustal thickness along the survey line varies from 30 to 35 km, being thickest in the vicinity of Point Hope, much more than expected from the present elevation of the top of the crust, just below sealevel. This modeling suggests four main layers: (1) an upper sedimentary layer up to 6 km thick with velocities between 3.5 and 5 km/s, (2) an upper crustal layer up to 15 km thick with velocities between 5.8 and 6.5 km/s, (3) a lower crustal layer up to 20 km thick with velocities of about 7 km/s, and (4) the upper mantle with a velocity of 8 km/s.

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© Richard M Allen