Location

New York, New York

Session Start Date

4-13-2004

Session End Date

4-17-2004

Abstract

The M 7.9 earthquake of November 3, 2002 event ruptured more than 340 kilometers on three fault, causing widespread liquefaction in the fluvial deposits of steep alpine valleys of the Alaska Range and eastern lowlands of the Tanana River. The event occurred in a remote and largely undeveloped portion of the rugged Alaskan central range, with few seismometer recordings. The areas affected by liquefaction are largely confined to native Holocene river deposits, areas bounded by stiffer ground moraine, Pleistocene uplands, and bedrock. Liquefaction affected areas of alluvial river valleys draining mountainous and glacier-proximal rivers. The most noteworthy observations are that liquefaction damage was focused towards the eastern end of the rupture area. In the western portion of the rupture zone, localized liquefaction developed in recent deposits of the Susitna and Delta rivers in the immediate vicinity of the surface rupture of the fault. More abundant and severe liquefaction occurred on the eastern Robertson, Slana, Tok, Chisana and, especially, Nabesna Rivers. In the Tanana lowland, liquefaction features were sparse on the western bars of the Tanana River in the vicinity of Fairbanks to west of Delta, but became pervasive throughout the eastern region from Delta to Northway. Though liquefaction observations were abundant, there was a dearth of instrumental recordings useful to relate damage effects to measured intensity. To characterize soil properties and stiffness of liquefaction evaluation sites, we used a portable spectral analysis of surface waves (SASW) apparatus to profile the shear wave velocity of the ground. On the Nabesna and Delta rivers that cross the fault, we only observe liquefaction features in soil deposits where normalized shear wave velocities fall below 230 m/s. Severity of sand boils, fissuring and lateral displacement of liquefied ground dramatically increase in soils of lower shear wave velocity, especially below 170 m/s. Some of the most pronounced ground failures are far from the fault zone (60-100 km) in extremely loose, low velocity (~120 m/s) fine sands of the bars of the Tanana River. Strong motion instrumentation was sparse within 150 kilometers of the fault rupture and the seismometers of Alyeska pump stations PS9 (PGA=0.09), PS10 (PGA=0.36g), and PS11 (PGA=0.09) serve as the principal strong motion recordings. Insufficient strong motion instrumentation is available to identify areas of amplified ground motion

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conference on Case Histories in Geotechnical Engineering

Meeting Name

Fifth Conference

Publisher

University of Missouri--Rolla

Publication Date

4-13-2004

Document Version

Final Version

Rights

© 2004 University of Missouri--Rolla, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

Share

 
COinS
 
Apr 13th, 12:00 AM Apr 17th, 12:00 AM

Geotechnical Observations of the November 3, 2002 M7.9 Denali Fault Earthquake

New York, New York

The M 7.9 earthquake of November 3, 2002 event ruptured more than 340 kilometers on three fault, causing widespread liquefaction in the fluvial deposits of steep alpine valleys of the Alaska Range and eastern lowlands of the Tanana River. The event occurred in a remote and largely undeveloped portion of the rugged Alaskan central range, with few seismometer recordings. The areas affected by liquefaction are largely confined to native Holocene river deposits, areas bounded by stiffer ground moraine, Pleistocene uplands, and bedrock. Liquefaction affected areas of alluvial river valleys draining mountainous and glacier-proximal rivers. The most noteworthy observations are that liquefaction damage was focused towards the eastern end of the rupture area. In the western portion of the rupture zone, localized liquefaction developed in recent deposits of the Susitna and Delta rivers in the immediate vicinity of the surface rupture of the fault. More abundant and severe liquefaction occurred on the eastern Robertson, Slana, Tok, Chisana and, especially, Nabesna Rivers. In the Tanana lowland, liquefaction features were sparse on the western bars of the Tanana River in the vicinity of Fairbanks to west of Delta, but became pervasive throughout the eastern region from Delta to Northway. Though liquefaction observations were abundant, there was a dearth of instrumental recordings useful to relate damage effects to measured intensity. To characterize soil properties and stiffness of liquefaction evaluation sites, we used a portable spectral analysis of surface waves (SASW) apparatus to profile the shear wave velocity of the ground. On the Nabesna and Delta rivers that cross the fault, we only observe liquefaction features in soil deposits where normalized shear wave velocities fall below 230 m/s. Severity of sand boils, fissuring and lateral displacement of liquefied ground dramatically increase in soils of lower shear wave velocity, especially below 170 m/s. Some of the most pronounced ground failures are far from the fault zone (60-100 km) in extremely loose, low velocity (~120 m/s) fine sands of the bars of the Tanana River. Strong motion instrumentation was sparse within 150 kilometers of the fault rupture and the seismometers of Alyeska pump stations PS9 (PGA=0.09), PS10 (PGA=0.36g), and PS11 (PGA=0.09) serve as the principal strong motion recordings. Insufficient strong motion instrumentation is available to identify areas of amplified ground motion