Geology topics

M.A. Khan

Publications and source records attributed to M.A. Khan.

5 recordsLinked to original sources

USGS2012

Group takes a fresh look at the lithosphere underneath southern Kenya

Since the turn of the century the well-developed Kenya rift has been a crucial location for studying the interrelationships between extension, uplift, and magmatism. In 1989–1990, an experiment conducted by the Kenya Rift International Seismic Project (KRISP) focused on the central and northern portions of Kenya (Figure 1) and provided a rich base of information regarding the structure and evolution of the rift, which answered many key questions and raised others. Does the crust thin to the south of the Kenya dome as it does to the north?, and if it does, which crustal layer would be mainly affected? How is the Chyulu Hills Quaternary volcanism related to the rifting process? What is the relationship between the crust and lithospheric mantle during extension?

East African Rift, Great Rift Valley, Gregory Rift↗

USGS1994

The KRISP 90 seismic experiment-a technical review

On the basis of a preliminary experiment in 1985 (KRISP 85), a seismic refraction/wide-angle reflection survey and a teleseismic tomography experiment were jointly undertaken to study the lithospheric structure of the Kenya rift down to depths of greater than 200 km. This report serves as an introduction to a series of subsequent papers and will focus on the technical description of the seismic surveys of the main KRISP 90 effort. The seismic refraction/wide-angle reflection survey was carried out in a 4-week period in January and February 1990. It consisted of three profiles: one extending along the rift valley from Lake Turkana to Lake Magadi, one crossing the rift at Lake Baringo, and one located on the eastern flank of the rift proper. A total of 206 mobile vertical-component seismographs, with an average station interval of about 2 km, recorded the energy of underwater and borehole explosions to distances of up to about 550 km. During the teleseismic survey an array of 65 seismographs was deployed to record teleseismic, regional and local events for a period of about 7 months from October 1989 to April 1990. The elliptical array spanned the central portion of the rift, with Nakuru at its center, and covered an area about 300 × 200 km, with an average station spacing of 10–30 km.

Tectonophysics↗

USGS1994

The East African rift system in the light of KRISP 90

On the basis of a test experiment in 1985 (KRISP 85) an integrated seismic-refraction/teleseismic survey (KRISP 90) was undertaken to study the deep structure beneath the Kenya rift down to depths of 100–150 km. This paper summarizes the highlights of KRISP 90 as reported in this volume and discusses their broad implications as well as the structure of the Kenya rift in the general framework of other continental rifts. Major scientific goals of this phase of KRISP were to reveal the detailed crustal and upper mantle structure under the Kenya rift, to study the relationship between mantle updoming and the development of sedimentary basins and other shallow structures within the rift, to understand the role of the Kenya rift within the Afro-Arabian rift system and within a global perspective and to elucidate fundamental questions such as the mode and mechanism of continental rifting. The KRISP results clearly demonstrate that the Kenya rift is associated with sharply defined lithospheric thinning and very low upper mantle velocities down to depths of over 150 km. In the south-central portion of the rift, the lithospheric mantle has been thinned much more than the crust. To the north, high-velocity layers detected in the upper mantle appear to require the presence of anistropy in the form of the alignment of olivine crystals. Major axial variations in structure were also discovered, which correlate very well with variations in the amount of extension, the physiographic width of the rift valley, the regional topography and the regional gravity anomalies. Similar relationships are particularly well documented in the Rio Grande rift. To the extent that truly comparable data sets are available, the Kenya rift shares many features with other rift zones. For example, crustal structure under the Kenya, Rio Grande and Baikal rifts and the Rhine Graben is generally symmetrically centered on the rift valleys. However, the Kenya rift is distinctive, but not unique, in terms of the amount of volcanism. This volcanic activity would suggest large-scale modification of the crust by magmatism. Although there is evidence of underplating in the form of a relatively high-velocity lower crustal layer, there are no major seismic velocity anomalies in the middle and upper crust which would suggest pervasive magmatism. This apparent lack of major modification is an enigma which requires further study.

Tectonophysics↗

USGS1991

Seroepidemiology of leptospirosis in Minnesota wolves

Serum samples (n = 457) from wolves (Canis lupus) in northern Minnesota were collected from 1972 through 1986 and were tested for antibodies against Leptospira interrogans using a microtiter agglutination test. Twelve serovars included in the study were: australis, autumnalis, ballum, bataviae, bratislava, canicola, copenhageni, grippotyphosa, hardjo, pomona, pyrogenes, and tarassovi. Fifty-two (11%) sera had antibody titers of greater than or equal to 1:50 against one or more serovars of L. interrogans. The seroprevalence of different serovars in decreasing order was: grippotyphosa, bratislava, autumnalis, canicola, pomona, ballum, pyrogenes, hardjo, and copenhageni. No antibodies were found against australis, bataviae, and tarassovi. These results indicate that L. interrogans infection may occur in wolves of Minnesota.

Journal of Wildlife Diseases↗

USGS1986

Antibodies against canine parvovirus of wolves of Minnesota: A serologic study from 1975 through 1985

Serum samples (n = 137) from 47 wild wolves (Canis lupus; 21 pups and 26 adults) were evaluated from 1975 to 1985 for antibodies against canine parvovirus, using the hemagglutination inhibition (HI) test. In addition, several blood samples (n = 35) from 14 of these wolves (6 pups and 8 adults) were evaluated simultaneously for erythrocyte and leukocyte counts, and for hemoglobin and blood urea nitrogen concentrations. Sixty-nine (50%) of the serum samples (35 wolves) had HI titers of greater than or equal to 256, whereas 68 (50%) of the samples (16 wolves) had HI titers of less than or equal to 128. Significant differences in the geometric mean titers were not found between pups and adults or between males and females. Of the 47 wolves evaluated, 12 (25%) developed a greater than or equal to fourfold increase in antibody titers during the 11-year period, with 2 wolves developing serologic conversions in 1976. The data indicate that canine parvovirus may have begun infecting wolves before or at the same time that it began infecting the dog population in the United States.

Journal of the American Veterinary Medical Associa↗