USGS Science⌕ Search

Geology topics

A.F. Chleborad

Publications and source records attributed to A.F. Chleborad.

12 recordsLinked to original sources
USGS2005

Regional landslide-hazard assessment for Seattle, Washington, USA

Landslides are a widespread, frequent, and costly hazard in Seattle and the Puget Sound area of Washington State, USA. Shallow earth slides triggered by heavy rainfall are the most common type of landslide in the area; many transform into debris flows and cause significant property damage or disrupt transportation. Large rotational and translational slides, though less common, also cause serious property damage. The hundreds of landslides that occurred during the winters of 1995-96 and 1996-97 stimulated renewed interest by Puget Sound communities in identifying landslide-prone areas and taking actions to reduce future landslide losses. Informal partnerships between the U.S. Geological Survey (USGS), the City of Seattle, and private consultants are focusing on the problem of identifying and mapping areas of landslide hazard as well as characterizing temporal aspects of the hazard. We have developed GIS-based methods to map the probability of landslide occurrence as well as empirical rainfall thresholds and physically based methods to forecast times of landslide occurrence. Our methods for mapping landslide hazard zones began with field studies and physically based models to assess relative slope stability, including the effects of material properties, seasonal groundwater levels, and rainfall infiltration. We have analyzed the correlation between historic landslide occurrence and relative slope stability to map the degree of landslide hazard. The City of Seattle is using results of the USGS studies in storm preparedness planning for emergency access and response, planning for development or redevelopment of hillsides, and municipal facility planning and prioritization. Methods we have developed could be applied elsewhere to suit local needs and available data.

Landslides↗
USGS2005

Rainfall characteristics for shallow landsliding in Seattle, Washington, USA

Shallow landsliding in the Seattle, Washington, area, has caused the occasional loss of human life and millions of dollars in damage to property. The effective management of the hazzard requires an understanding of the rainfall conditions that result in landslides. We present an empirical approach to quantify the antecedent moisture conditions and rainstorm intensity and duration that have triggered shallow landsliding using 25 years of hourly rainfull data and a complementary record of landslide occurrence. Our approach combines a simple water balance to estimate the antecedent moisture conditions of hillslope materials and a rainfall intensity-duration threshold to identify periods when shallow landsliding can be expected. The water balance is calibrated with field-monitoring data and combined with the rainfall intensity-duration threshold using a decision tree. Results are cast in terms of a hypothetical landslide warning system. Two widespread landslide events are correctly identified by the warning scheme; however, it is less accurate for more isolated landsliding. Copyright ?? 2005 John Wiley & Sons, Ltd.

Earth Surface Processes and Landforms↗
USGS1994

Modeling and analysis of the 1949 Narrows landslide, Tacoma, Washington

A large landslide failed catastrophically along steep, 90-m (300-ft) high bluffs overlooking the waters of Puget Sound at Tacoma, Washington, in April of 1949, three days after the region was struck by a magnitude 7.1 earthquake. The area of failure was investigated to estimate the static and seismic stability of the pre-earthquake slope and to identify factors that contributed to the failure. Results of static analyses suggest that the slope was marginally stable and that high ground-water conditions would have significantly reduced slope stability. The Newmark analysis of dynamic (seismic) slope stability was used to calculate predicted inertial displacements for the landslide for a range of possible material property and ground-water conditions. Comparison of predicted displacements with a reported displacement suggests that the ground motion could have initiated the large-scale failure. Results of the study provide a basis for discussion and comparison of similar bluffs in the Puget Sound region that may be susceptible to catastrophic, earthquake-induced slope failure.

Washington↗
USGS1987

Government Draw Bentonite Beds: a newly identified stratigraphic marker in the Virgin Creek Member of the Pierre Shale, central South Dakota ( USA).

A grouping of four bentonite beds, herein named the Government Draw Bentonite Beds, is identified as a stratigraphic marker within the Virgin Creek Member of the Pierre Shale. The beds are found west of Pierre, South Dakota, over an area of at least 130 mi2 (210 km2) where no other markers within the Virgin Creek Member have been identified. In this area, the Government Draw is a potential tool needed to determine the stratigraphic and structural relationships within the upper part of the Pierre Shale, heretofore little known. A better understanding of structural elements found in the Pierre Shale is needed to unravel the Late Cretaceous and younger geologic history of the area. -Authors

Mountain Geologist↗
USGS1986

Isopach and structure contour mapping of thin bentonite and shale beds in an area of mapped lineaments, central South Dakota

The N aquifer is an important source of water in the 5,400 square-mile Black Mesa area on the Navajo and Hopi Indian Reservations, Arizona. The Black Mesa monitoring program is designed to monitor long-term effects on the groundwater resources of the mesa as part of withdrawals from the aquifer by the strip-mining operation of Peabody Coal Co. Withdrawals from the N aquifer by the mine increased from 95 acre-feet in 1968 to more than 4,000 acre-feet in 1984. In 1985, withdrawals from the mine wells were temporarily reduced to about 2,500 acre-feet. Water levels in the confined area of the aquifer declined as much as 87 feet from 1965 to 1985 in some municipal and observation wells within about a 15-mile radius of the mine well field. In 1986, measurements indicated some recovery in water levels in most of these wells because of an approximate 90-percent reduction in pumpage from Peabody Coal Co. wells during the last half of 1985. Part of the drawdown in municipal wells is due to local pumpage. Water levels have not declined in wells tapping the unconfined area of the aquifer. Chemical analyses indicate no significant changes in the quality of water from wells that tap the N aquifer or from springs that discharge from several stratigraphic units, including the N aquifer, since pumping began at the mine. (USGS)

Open-File Report↗