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Geology topics

D. K. Keefer

Publications and source records attributed to D. K. Keefer.

31 records · Page 2Linked to original sources
USGS1993

The susceptibility of rock slopes to earthquake-induced failure

Faulure of rock slopes is a major cause of damage and casualties during moderate and strong earthquakes. This article presents a method for assessing the seismic stability of rock slopes, which can be applied on a regional scale, using data from existing maps, reports, aerial photographs, and reconnaissance-level field observations. The method is based on observed associations between landslide concentrations and slope characteristics in 24 earthquakes that occurred in various parts of the world.

Bulletin of the Association of Engineering Geologi↗
USGS1993

Landslides caused by the Klamath Falls, Oregon, earthquakes of September 20, 1993

The Klamath Falls earthquakes caused landslides throughout an area of about 420 sq km and as far as about 29 km from the epicenter, a distribution that is typical for magnitude 6 earthquakes (see graphs on following pages). Most of the landslides were rock falls or shallow, highly disrupted rock slides from roadcuts, quarries, and steep bluff faces. Such landslides are also among the most common types caused by other earthquakes of comparable magnitude. In the Klamath Falls area, the most numerous earthquake-induced rock falls were along the east-to southeast-facing flank of a ridge immediately south and west of Howard Bay (locality 1 on the accompanying map), 18 km east-southeast of the epicenter of the magntiude 6.0 shock at 10:45 p.m. This ridge is more than 240 m high and has slopes steeper than 45 ° in places. The upper part of the ridge is composed of material from basaltic lava flows, an the lower slopes are covered with colluvium and talus deposits containing abundant boulders.

Oregon↗
USGS1992

Surface effects of the earthquakes

The April 25-26, 1992, earthquakes caused significant changes in the landscape of the Cape Mendocino region. Although fault rupture did not break through to the surface, effects on the landscape included landslides, ground cracking due to strong shaking, liquefaction features (described later in this article), and uplift along the coast. The location map on the next page shows the distribution of some of these features.

California↗
USGS1989

Statistical analysis of factors affecting landslide distribution in the new Madrid seismic zone, Tennessee and Kentucky

More than 220 large landslides along the bluffs bordering the Mississippi alluvial plain between Cairo, Ill., and Memphis, Tenn., are analyzed by discriminant analysis and multiple linear regression to determine the relative effects of slope height and steepness, stratigraphic variation, slope aspect, and proximity to the hypocenters of the 1811-12 New Madrid, Mo., earthquakes on the distribution of these landslides. Three types of landslides are analyzed: (1) old, coherent slumps and block slides, which have eroded and revegetated features and no active analogs in the area; (2) old earth flows, which are also eroded and revegetated; and (3) young rotational slumps, which are present only along near-river bluffs, and which are the only young, active landslides in the area. Discriminant analysis shows that only one characteristic differs significantly between bluffs with and without young rotational slumps: failed bluffs tend to have sand and clay at their base, which may render them more susceptible to fluvial erosion. Bluffs having old coherent slides are significantly higher, steeper, and closer to the hypocenters of the 1811-12 earthquakes than bluffs without these slides. Bluffs having old earth flows are likewise higher and closer to the earthquake hypocenters. Multiple regression analysis indicates that the distribution of young rotational slumps is affected most strongly by slope steepness: about one-third of the variation in the distribution is explained by variations in slope steepness. The distribution of old coherent slides and earth flows is affected most strongly by slope height, but the proximity to the hypocenters of the 1811-12 earthquakes also significantly affects the distribution. The results of the statistical analyses indicate that the only recently active landsliding in the area is along actively eroding river banks, where rotational slumps formed as bluffs are undercut by the river. The analyses further indicate that the old coherent slides and earth flows in the area are spatially related to the 1811-12 earthquake hypocenters and were thus probably triggered by those earthquakes. These results are consistent with findings of other recent investigations of landslides in the area that presented field, historical, and analytical evidence to demonstrate that old landslides in the area formed during the 1811-12 New Madrid earthquakes. Results of the multiple linear regression can also be used to approximate the relative susceptibility of the bluffs in the study area to seismically induced landsliding.

Kentucky, Tennessee↗
USGS1986

Seismically induced landslides: current research by the US Geological Survey.

We have produced a regional seismic slope-stability map and a probabilistic prediction of landslide distribution from a postulated earthquake. For liquefaction-induced landslides, in situ measurements of seismically induced pore-water pressures have been used to establish an elastic model of pore pressure generation. -from Authors

Geologia Applicata e Idrogeologia↗
USGS1985

Map showing ground failures from the Greenville/Mount Diablo earthquake sequence of January 1980, Northern California

The Greenville/Mt. Diablo earthquake sequence of January 24-26, 1980, was composed of Small and moderate earthquakes; the two largest shocks, on January 24 and 26, were of magnitudes (M) 5.5 and 5.6, respectively (Bolt and others, 1981). A 5.5 event is at the lower end of the range of earthquake magnitudes which cause observable ground failure (Youd and Perkins, 1978; Keefer, 1984). While none of the slope failures produced by the Greenville/Mt. Diablo earthquake sequence (GMDES) was larger than a few tens of cubic meters, they were both widespread in area (see map) and rich in variety, and thus have much to teach us about seismically induced slope failures in the San Francisco Bay area. This map depicts the location, type, and relative size of the ground failures observed during our reconnaissance, which began at 2:30 pm PST on January 24 and continued on January 25, 26, and 28 and February 6. Our observations were generally limited to that part of the Livermore region that is accessible by state and county roads. Information about the individual ground failures may be obtained from the map and the brief descriptions in table 1. The following text is a general discussion of the distribution and the mechanisms of the ground failures, followed by a discussion of the effects of wet winter conditions and of topographic amplification on the distribution and mechanisms of slope failure, and it concludes with a description of our (unsuccessful) efforts to locate any ground failures due to liquefaction. The discussion is intended not only to describe the GMDES slope failures but also to place them into the larger general context of seismically induced slope failures.

California↗
USGS1984

Rock avalanches caused by earthquakes: Source characteristics

Study of a worldwide sample of historical earthquakes showed that slopes most susceptible to catastrophic rock avalanches were higher than 150 meters and steeper than 25 degrees. The slopes were undercut by fluvial or glacial erosion, were composed of intensely fractured rock, and exhibited at least one other indicator of low strength or potential instability.

Science↗
USGS1984

Landslides caused by earthquakes

Data from 40 historical world-wide earthquakes were studied to determine the characteristics, geologic environments, and hazards of landslides caused by seismic events. This sample of 40 events was supplemented with intensity data from several hundred United States earthquakes to study relations between landslide distribution and seismic parameters. Fourteen types of landslides were identified in the earthquakes studied. The most abundant of these were rock falls, disrupted soil slides, and rock slides. The greatest losses of human life were due to rock avalanches, rapid soil flows, and rock falls. Correlations between magnitude (M) and landslide distribution show that the maximum area likely to be affected by landslides in a seismic event increases from approximately 0 at M ≅ 4.0 to 500,000 km 2 at M = 9.2. Threshold magnitudes, minimum shaking intensities, and relations between M and distance from epicenter or fault rupture were used to define relative levels of shaking that trigger landslides in susceptible materials. Four types of internally disrupted landslides—rock falls, rock slides, soil falls, and disrupted soil slides—are initiated by the weakest shaking. More coherent, deeper-seated slides require stronger shaking; lateral spreads and flows require shaking that is stronger still; and the strongest shaking is probably required for very highly disrupted rock avalanches and soil avalanches. Each type of earthquake-induced landslide occurs in a particular suite of geologic environments. These range from overhanging slopes of well-indurated rock to slopes of less than 1° underlain by soft, unconsolidated sediments. Materials most susceptible to earthquake-induced landslides include weakly cemented rocks, more-indurated rocks with prominent or pervasive discontinuities, residual and colluvial sand, volcanic soils containing sensitive clay, loess, cemented soils, granular alluvium, granular deltaic deposits, and granular man-made fill. Few earthquake-induced landslides reactivate older landslides; most are in materials that have not previously failed.

Geological Society of America Bulletin↗