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Edwin L. Harp

Publications and source records attributed to Edwin L. Harp.

30 records · Page 2Linked to original sources
USGS2004

Hazard analysis of landslides triggered by Typhoon Chata’an on July 2, 2002, in Chuuk State, Federated States of Micronesia

More than 250 landslides were triggered across the eastern volcanic islands of Chuuk State in the Federated States of Micronesia by torrential rainfall from tropical storm Chata’an on July 2, 2002. Landslides triggered during nearly 20 inches of rainfall in less than 24 hours caused 43 fatalities and the destruction or damage of 231 structures, including homes, schools, community centers, and medical dispensaries. Landslides also buried roads, crops, and water supplies. The landslides ranged in volume from a few cubic meters to more than 1 million cubic meters. Most of the failures began as slumps and transformed into debris flows, some of which traveled several hundred meters across coastal flatlands into populated areas. A landslide-inventory map produced after the storm shows that the island of Tonoas had the largest area affected by landslides, although the islands of Weno, Fefan, Etten, Uman, Siis, Udot, Eot, and Fanapanges also had significant landslides. Based on observations since the storm, we estimate the continuing hazard from landslides triggered by Chata’an to be relatively low. However, tropical storms and typhoons similar to Chata’an frequently develop in Micronesia and are likely to affect the islands of Chuuk in the future. To assess the landslide hazard from future tropical storms, we produced a hazard map that identifies landslide-source areas of high, moderate, and low hazard. This map can be used to identify relatively safe areas for relocating structures or establishing areas where people could gather for shelter in relative safety during future typhoons or tropical storms similar to Chata’an.

Chuuk State↗
USGS2002

Identifying a large landslide with small displacements in a zone of coseismic tectonic deformation; the Villa Del Monte landslide triggered by the 1989 Loma Prieta, California, earthquake

The Villa Del Monte landslide was one of 20 large and complex landslides triggered by the 1989 Loma Prieta , California , earthquake in a zone of pervasive coseismic ground cracking near the fault rupture. The landslide was approximately 980 m long, 870 m wide, and encompassed an area of approximately 68 ha. Drilling data suggested that movement may have extended to depths as great as 85 m below the ground surface. Even though the landslide moved <1 m, it caused substantial damage to numerous dwellings and other structures, primarily as a result of differential displacements and internal Assuring. Surface cracks, scarps, and compression features delineating the Villa Del Monte landslide were discontinuous, probably because coseismic displacements were small ; such discontinuous features were also characteristic of the other large , coseismic landslides in the area, which also moved only short distances during the earthquake . Because features marking landslide boundaries were discontinuous and because other types of coseismic ground cracks were widespread in the area, identification of the landslides required detailed mapping and analysis. Recognition that landslides such as that at Villa Del Monte may occur near earthquake-generating fault ruptures should aid in future hazard evaluations of areas along active faults.

Reviews in Engineering Geology↗
USGS2002

Anomalous concentrations of seismically triggered rock falls in Pacoima Canyon: Are they caused by highly susceptible slopes or local amplification of seismic shaking?

Anomalously high concentrations of rock falls were triggered in Pacoima Canyon (Los Angeles, California) during the 1994 Northridge earthquake. Similar concentrations were also documented from the 1971 San Fernando earthquake. Using an engineering rock-mass classification that evaluates the susceptibility of rock slopes to seismic failure based on the fracture properties of a rock mass (in terms of a numerical "Q-value" that describes rock quality), the rock slopes in Pacoima Canyon were compared with rock slopes in sorrounding areas where topography and lithology are similar, but rock-fall concentrations from the earthquakes were much lower. A statistical comparison of Q-values from five sites surrounding Pacoima Canyon indicates that seismic susceptibilities are similar to those within Pacoima Canyon; differences in the characteristics of rock slopes between these sites are not sufficient to account for the relatively high concentrations of rock falls within Pacoima Canyon as compared to low concentrations elsewhere. By eliminating susceptibility differences as a cause, the most likely explanations for the differences in rock-fall concentrations is anomalously high shaking levels in Pacoima Canyon, possibly resulting from topographic amplification within the canyon.

Bulletin of the Seismological Society of America↗
USGS2002

Landslides triggered by Hurricane Mitch in Tegucigalpa, Honduras

The arrival of Hurricane Mitch in Honduras in the latter part of the 1998 hurricane season produced effects that were unprecedented in their widespread nature throughout Central America. After winds from the storm had blown down more than 70 percent of the conifer forest on the Bay Island of Guanaja, the hurricane turned inland and stalled over the mainland of Honduras for 3 days. The resulting deluge of rainfall produced devastating flooding and landslides that resulted in more than 9,000 fatalities and 3 million people displaced. Although the eye of Hurricane Mitch passed through the northern part of Honduras, the greatest rainfall totals and intensities occurred in the southern part of the country near Choluteca. For the three days October 29-31, 1998, total rainfall at Choluteca exceeded 900 mm. Not surprisingly, it was in this area that the highest landslide concentrations occurred.

Open-File Report↗
USGS2002

Digital inventory of landslides and related deposits in Honduras triggered by Hurricane Mitch

Intense rainfall from Hurricane Mitch from October 27-31, 1998, exceeded 900 mm in places in Honduras and triggered in excess of 500,000 landslides throughout the country. Landslides damaged an estimated 70% of the road network in Honduras based on estimates by the U. S Army Corps of Engineers. Numbers of fatalities due to landslides are not accurately known due to the fact that numerous small villages throughout Honduras lost residents to landslides without an official count being recorded. A conservative estimate would place the number at near 1,000. Debris flows accounted for over 95% of the landslides and ranged in thickness from 1 to 15 m. Flow path lengths of these failures ranged from several meters to 7.5 km. The highest concentrations of debris flows occurred in the mountains near the town of Choluteca where over 900 mm of rain fell in three days. Although landslides other than debris flows were few, several deep-seated landslides in the city of Tegucigalpa severely impacted people and property. The 'El Berrinche' rotational slump/earth flow of approximately six million cubic meters volume destroyed the entire neighborhood of Colonia Soto near the center of the city. The landslide also dammed the Rio Choluteca and created a lagoon behind the landslide dam, which immediately posed a health problem for the city, because raw, untreated sewage was emptying into the Rio Choluteca. Several areas of highly concentrated landslides have been responsible for much of the flooding problem as well. Huge sediment influxes from landslide source areas near La Ceiba, La Libertad, Marale, and in several arms of El Cajon Reservoir have reduced stream capacities to practically nothing and have exacerbated flooding conditions in even the moderate rainfall seasons since Hurricane Mitch. The ongoing hazard to communities from landslides triggered during Hurricane Mitch are being analyzed using aerial photography taken by the U.S. Air Force and by supplemental photography taken by local contractors. Through the use of digital elevation models derived from 1:50,000-scale topographic maps and geologic maps, landslide susceptibility maps will be derived to aid land-use planning and relocation efforts.

Open-File Report↗
USGS2001

Assessment of landslide hazards resulting from the February 13, 2001, El Salvador earthquake; a report to the government of El Salvador and the U. S. Agency for International Development

On February 13, 2001, a magnitude 6.5 earthquake occurred about 40 km eastsoutheast of the capital city of San Salvador in central El Salvador and triggered thousands of landslides in the area east of Lago de Ilopango. The landslides are concentrated in a 2,500-km2 area and are particularly abundant in areas underlain by thick deposits of poorly consolidated, late Pleistocene and Holocene Tierra Blanca rhyolitic tephras that were erupted from Ilopango caldera. Drainages in the tephra deposits are deeply incised, and steep valley walls failed during the strong shaking. Many drainages are clogged with landslide debris that locally buries the adjacent valley floor. The fine grain-size of the tephra facilitates its easy mobilization by rainfall runoff. The potential for remobilizing the landslide debris as debris flows and in floods is significant as this sediment is transported through the drainage systems during the upcoming rainy season. In addition to thousands of shallow failures, two very large landslides occurred that blocked the Rio El Desague and the Rio Jiboa. The Rio El Desague landslide has an estimated volume of 1.5 million m3, and the Rio Jiboa landslide has an estimated volume of 12 million m3. Field studies indicate that catastrophic draining of the Rio El Desague landslide-dammed lake would pose a minimal flooding hazard, whereas catastrophic draining of the Rio Jiboa lake would pose a serious hazard and warrants immediate action. Construction of a spillway across part of the dam could moderate the impact of catastrophic lake draining and the associated flood. Two major slope failures on the northern side of Volcan San Vicente occurred in the upper reaches of Quebrada Del Muerto and the Quebrada El Blanco. The landslide debris in the Quebrada Del Muerto consists dominantly of blocks of well-lithified andesite, whereas the debris in the Quebrada El Blanco consists of poorly consolidated pyroclastic sediment. The large blocks of lithified rock in Quebrada Del Muerto are unlikely to be remobilized during the rainy season; whereas, the sandy and silty landslide debris in the channel of Quebrada El Blanco is susceptible to remobilization as debris flows that could extend into populated areas on the lower slopes of the volcano. Around the northern and eastern shore of Lago de Ilopango, earthquake-induced liquefaction and lateral-spreading landslides caused local damage to homes and other structures; this damage was most prevalent in the village of San Agustin. San Agustin is also potentially threatened by floods because it is located on the alluvial fan of the Quebrada El Chaguite drainage basin, which contains hundreds of landslides that have choked numerous small channels with volcanic tephra. As the easily eroded tephra is transported down the drainage system and deposited on the alluvial fan, it could clog the currently active channel with sediment, divert the stream into a new channel, and possibly direct flow through San Agustin, causing more damage and destruction

Open-File Report↗
USGS1998

A method for producing digital probabilistic seismic landslide hazard maps: An example from the Los Angeles, California, area

The 1994 Northridge, California, earthquake is the first earthquake for which we have all of the data sets needed to conduct a rigorous regional analysis of seismic slope instability. These data sets include (1) a comprehensive inventory of triggered landslides, (2) about 200 strong-motion records of the mainshock, (3) 1:24,000-scale geologic mapping of the region, (4) extensive data on engineering properties of geologic units, and (5) high-resolution digital elevation models of the topography. All of these data sets have been digitized and rasterized at 10-m grid spacing in the ARC/INFO GIS platform. Combining these data sets in a dynamic model based on Newmark's permanent-deformation (sliding-block) analysis yields estimates of coseismic landslide displacement in each grid cell from the Northridge earthquake. The modeled displacements are then compared with the digital inventory of landslides triggered by the Northridge earthquake to construct a probability curve relating predicted displacement to probability of failure. This probability function can be applied to predict and map the spatial variability in failure probability in any ground-shaking conditions of interest. We anticipate that this mapping procedure will be used to construct seismic landslide hazard maps that will assist in emergency preparedness planning and in making rational decisions regarding development and construction in areas susceptible to seismic slope failure.

California↗
USGS1995

Inventory of landslides triggered by the 1994 Northridge, California earthquake

The 17 January 1994 Northridge, California, earthquake (M=6.7) triggered more than 11,000 landslides over an area of about 10,000 km?. Most of the landslides were concentrated in a 1,000-km? area that includes the Santa Susana Mountains and the mountains north of the Santa Clara River valley. We mapped landslides triggered by the earthquake in the field and from 1:60,000-scale aerial photography provided by the U.S. Air Force and taken the morning of the earthquake; these were subsequently digitized and plotted in a GIS-based format, as shown on the accompanying maps (which also are accessible via Internet). Most of the triggered landslides were shallow (1-5 m), highly disrupted falls and slides in weakly cemented Tertiary to Pleistocene clastic sediment. Average volumes of these types of landslides were less than 1,000 m?, but many had volumes exceeding 100,000 m?. Many of the larger disrupted slides traveled more than 50 m, and a few moved as far as 200 m from the bases of steep parent slopes. Deeper ( >5 m) rotational slumps and block slides numbered in the hundreds, a few of which exceeded 100,000 m? in volume. The largest triggered landslide was a block slide having a volume of 8X10E06 m?. Triggered landslides damaged or destroyed dozens of homes, blocked roads, and damaged oil-field infrastructure. Analysis of landslide distribution with respect to variations in (1) landslide susceptibility and (2) strong shaking recorded by hundreds of instruments will form the basis of a seismic landslide hazard analysis of the Los Angeles area.

Open-File Report↗
USGS1989

Map showing 1983 landslides in Utah

The State of Utah sustained direct damages from landslides and flooding in excess of $400 million during approximately three months in the spring of 1983. These disastrous events were declared national disaster areas (Anderson and others, 1985).

Utah↗