Serving professionals in engineering, environmental, and groundwater geology
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APRIL MEETING NOTICE
***Wednesday, April 10, 2013***

Topic: "Translational Sheet Landsliding in the Pacific Palisades and its Relevance to Safety Factor Calculation"

Speaker: E. D. Michael, CEG
Consultant Geologist

Location: Cisco's Restaurant
925 S. Westlake Boulevard, Westlake Village, CA
(805) 778-1191

Date/Time: Wednesday, April 10, 2013
5:45pm - Social Hour
6:45pm - Dinner
7:45pm - Program

Cost: $30 per person with reservations in advance for AEG members, $35 without reservations (at the door), $15 for students with a valid Student ID

RSVP: Please email Shant Minas at: shant@aessoil.com
or call (818) 552-6000 ext.109
Please make reservations by e-mail prior to
1 p.m., Tuesday, April 9, 2013


Abstract
TRANSLATIONAL SHEET LANDSLIDING IN THE PACIFIC PALISADES
and ITS RELEVANCE TO SAFETY FACTOR CALCULATION with ADDITIONAL NOTES ON OIL-SHALE DEVELOPMENT


E.D. Michael
March 19, 2013

McGill (1989) mapped three extensive masses of older landslide debris In the Pacific Palisades sea cliff along Pacific Coast Highway between Potrero Canyon and Sunset Boulevard in the City of Los Angeles. The slides are clearly translational and quite likely single units rather than slide complexes. All have been derived from the Modelo Formation and at least in two cases they have carried with them sections of overlying Pleistocene terrace deposits. Those deposits are laid on the what McGill calls the Pacific Palisades platform, a wave-cut surface he correlates with the Dume terrace of Davis (1934) to which Birkeland (1979) has assigned a date of around 104,000 years bp. From east to west, these are referred to here as the Tahitian Terrace slide ( 20 acres), the Bay Club slide (18 acres) and the Sunset Towers slide ( 8 acres). As so far determined, none is known to be thicker than about 40 feet. Such a disparity in the thickness-area ratio - in the range of 10-4 to 10-5 - justifies referring to them as "sheets." These features demand explanation not only in terms of the mechanics involved but also regarding their significance in terms of current efforts to redevelop properties they underlie.

The evidence strongly suggests that these translational slide sheets are unique in California, although the circumstances may be similar to some coastal areas farther north. They are a result of a sequence of events beginning with the depositional environment of the basal Modelo Formation in early late Miocene time with anaerobic bacterial reduction of brackish-water sulfate to pyrite or marcasite, deep burial and then exposure to the atmosphere during current tectonic uplift believed to have begun in Pleistocene time, sea-cliff steepening by wave erosion as a result of the Flandrian transgression now in progress, alteration of the secondary iron sulfides to the potassium-iron sulfate, jarosite involving volumetric increase of perhaps 350 percent, with consequent fracturing and loss of bulk cohesion in surficial zones, followed by landsliding in response to seismic acceleration. The geological character of these translational sheet slides in the Pacific Palisades sea cliff is such that failure due to area-wide high ground-water levels is extremely unlikely. They all could be due to a single large-magnitude earthquake.

Of most concern is the fact that such a bulk loss of cohesion calls into question the common method of slope-stability analysis used to demonstrate a safety factor of 1.5 in such materials as current City Building and Safety Code policy requires. It is clear that the bulk cohesion - by which is meant the cohesive strength of the debris mass as a unit - has no relationship to cohesion commonly determined by direct shear tests individual formation specimens upon which, in practice, calculations of safety factors for specific sites now are almost invariably based.

The extensive fracturing due to alteration of iron sulfides to sulfates such as jarosite has an interesting serendipitous aspect regarding oil-shale development. Now being widely considered for Miocene sections in California, this is certain to raise environmental objections - among them ground-water contamination - as is now reported to be the case in Colorado due to effects of hydrofracking. Consequently, the oil industry may well consider an alternative procedure - call it airfracking - to be achieved from oxygen-induced alteration of the sulfides. The evidence suggests that such alteration occurs quite rapidly, probably on the order of a few months. Although probably not so efficient as the mechanical application water pressure force, this might be significantly ameliorated by a large number of injection points.

References:
Birkeland, Peter W., 1972, Late Quaternary eustatic sea-level changes along the Malibu Coast, Los Angeles, County, California: Jour. Geol. Vol. 80, pp. 432-448

Davis, W.M., 1933, Glacial epochs of the Santa Monica Mountains, California: Geol Soc. America Bull., Vol. 44, No. 5, pp. 1041-1133.

McGill, John T., 1989, Geologic maps of the Pacific Palisades area, City of Los Angeles, California: U.S. Geol. Survey Misc. Investigation Series Map I-1828.
 
Speaker Biography
Eugene D. Michael

Don Michael was born in Spokane, Washington, and although living in San Diego and Hawthorne, Nevada when he was young, his later youth was spent in West Los Angeles. Upon graduation from University High School in 1946, he enlisted in the U.S. Navy. After two year's service, he was honorably discharged and began his advanced education earning a BA in geology from Occidental College in 1953. His professional career was first as a Jr. EG with the State Division of Water Resources and then as an Asst. EG with the State Division of Highways. During that period, he joined with about twenty-five other local geologists, mostly public agency employees, to form the Los Angeles section of the California Association of Engineering Geologists, later AEG. In 1955, he enrolled in UCLA, graduating with an MA in geology in 1960 with minors in mathematics and physical science. During that period, which was prior to State licensing for geologists, he began private consulting, being among the first fifteen or so geologists from whom local agencies accepted reports concerning property development as required under initially established grading codes.

Don began full-time private consulting in engineering geology and hydrogeology in 1960. However, from 1966 to 1970, he worked in Viet Nam for two years with Pope Evans and Robbins of New York, primarily on ground-water problems for US military bases, and then two years on the staff of the Science Advisor, Military Assistance Command, Viet Nam, on a variety of military projects. When leaving that post as requirements for the work of the Science Advisor began to diminish, he was awarded by the Commanding General a Department of Defense Certificate of Appreciation for his work in support of the US and other Free World military forces. Upon return to California, he again took up consulting. Over the years, he has maintained an academic interest in various geologic subjects and publishes from time to time. Recently, he established a web site, "Malibu Geology, Then and Now," and he continues research for a book on the lives of Ethan Allen and Hosea Ballou Grosh, the discovers of the Comstock Lode.