A high-resolution seismic reflection/refraction study of the Chugach-Peninsular terrane boundary, southern Alaska

Journal of Geophysical Research Solid Earth
By: , and 

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Abstract

We present results from a high-resolution seismic refraction analysis of the shallow (approximately 2 km) crustal structure along the 107-km-long Trans-Alaska Crustal Transect Chugach reflection line in southern Alaska and a comparison with laboratory measurements of field samples. The refraction analysis includes the two-dimensional interpretation of several thousand first- and secondary-arrival travel times digitized from 1024-channel split-spread common shot gathers. The velocity model derived from this analysis better defines the location and geometry of terrane boundaries than does the normal incidence reflection section and agrees well with surface mapping of lithologies. Furthermore, the model predicts travel times within 100 ms of the reflection times recorded from the base of the Quaternary on the Chugach reflection section. Thicknesses of Quaternary deposits, with velocities between 1.1 and 2.0 km/s, correlate inversely with the quantity of observed lower crustal reflections on the Chugach section, suggesting that the presence or absence of these sediments in sufficient thickness exerted primary control on the quality of the deeper portion of the section. There is a significant velocity contrast between crystalline rocks across the Border Ranges fault (5.0 versus 5.6 km/s), the major contact between the Chugach and Peninsular terranes, in agreement with laboratory measurements of field specimens. In the Peninsular terrane the modeling indicates that an unnamed fault delimiting the southern flank of the Copper River Basin dips steeply northward at 50° and has about 1300 m of vertical offset. Laboratory measurements document a maximum velocity anisotropy of 20% for phyllitic schists of the Valdez Group in the Chugach terrane. In agreement with the observed E-W strike and near-vertical dip of the Valdez Group, we determined a significant (14%) velocity anisotropy for ray paths oriented N-S versus NE-SW.

Publication type Article
Publication Subtype Journal Article
Title A high-resolution seismic reflection/refraction study of the Chugach-Peninsular terrane boundary, southern Alaska
Series title Journal of Geophysical Research Solid Earth
DOI 10.1029/JB094iB04p04441
Volume 94
Issue B4
Year Published 1989
Language English
Publisher American Geophysical Union
Description 15 p.
First page 4441
Last page 4455
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