• journal_title：Bulletin of the Seismological Society of America
• Contributor：Julie B. Willis ; Peter J. Haeussler ; Ronald L. Bruhn ; Grant C. Willis
• Publisher：Seismological Society of America
• Date：2007-
• Format：text/html
• Language：en
• Identifier：10.1785/0120060109
• journal_abbrev：Bulletin of the Seismological Society of America
• issn：0037-1106
• volume：97
• issue：3
• firstpage：1019
• section：Short Notes

The western segment of the Castle Mountain fault poses a significant seismic hazard to the most populated region of south-central Alaska. We identify a previously unrecognized margin of a postglacial outwash channel that is offset right laterally 36 ± 4 m across the western segment of the Castle Mountain fault. This offset occurred after glaciers withdrew from the lowland 11,300–15,380 cal yr lass="sc">b.p. and after outwash channel margins were cut and stabilized 11,210–13,470 cal yr lass="sc">b.p. Using these ages and the measured separation, we obtain a maximum slip rate of 3.0 ± 0.6 mm yr⁻¹ and a minimum slip rate of 2.8 ± 0.7 mm yr⁻¹. These are the first lateral slip rates for the Castle Mountain fault established by a field measurement. Based on timing of the most recent earthquake, 670 ± 60 yr lass="sc">b.p., the Castle Mountain fault could have accumulated an average single-event slip of about 1.9 m (extremes range from 1.3 to 2.6 m). The fault consists of two segments; a surface-rupturing earthquake likely will be limited to the 62-km-long western segment. Area-magnitude regression calculations suggest that such an earthquake on the western Castle Mountain fault would have a moment magnitude of 6.9 to 7.3.