Rupture process of large earthquakes in the northern Mexico subduction zone

The Cocos plate subducts beneath North America at the Mexico trench. The northernmost segment of this trench, between the Orozco and Rivera fracture zones, has ruptured in a sequence of five large earthquakes from 1973 to 1985; the Jan. 30, 1973 Colima event ( M s 7.5) at the northern end of the segment near Rivera fracture zone; the Mar. 14, 1979 Petatlan event ( M s 7.6) at the southern end of the segment on the Orozco fracture zone; the Oct. 25, 1981 Playa Azul event ( M s 7.3) in the middle of the Michoacan “gap”; the Sept. 19, 1985 Michoacan mainshock ( M s 8.1); and the Sept. 21, 1985 Michoacan aftershock ( M s 7.6) that reruptured part of the Petatlan zone. Body wave inversion for the rupture process of these earthquakes finds the best: earthquake depth; focal mechanism; overall source time function; and seismic moment, for each earthquake. In addition, we have determined spatial concentrations of seismic moment release for the Colima earthquake, and the Michoacan mainshock and aftershock. These spatial concentrations of slip are interpreted as asperities; and the resultant asperity distribution for Mexico is compared to other subduction zones. The body wave inversion technique also determines the Moment Tensor Rate Functions ; but there is no evidence for statistically significant changes in the moment tensor during rupture for any of the five earthquakes. An appendix describes the Moment Tensor Rate Functions methodology in detail.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43169/1/24_2004_Article_BF00875970.pd

Crosslinking process and properties of unconventional blends of chloroprene rubber and partially hydrogenated acrylonitrile-butadiene rubber

Zbadano właściwości niekonwencjonalnych mieszanin podatnego na krystalizację i termosieciowanie kauczuku chloroprenowego (CR) z częściowo uwodornionym (> 95 % mol) kauczukiem butadienowo-akrylonitrylowym (THNBR). Mieszaniny sporządzano stosując metodę reaktywnego przetwórstwa, połączonego z dynamicznym, selektywnym termosieciowaniem CR, a następnie sieciowania w temperaturze 433 K disiarczkiem tetrametylotiuramu (TMTD), w obecności ZnO. Zbadano kinetykę sieciowania oraz właściwości mechaniczne przy rozciąganiu oraz metodą mikroskopii sił atomowych (AFM) określono morfologię mieszanin, a na podstawie pęcznienia równowagowego w rozpuszczalnikach stopień ich usieciowania. Stwierdzono, że mieszaniny CR/THNBR, zawierające 25—45 phr uprzednio termousieciowanego CR, a następnie usieciowane za pomocą TMTD/ZnO, charakteryzują się wyższym stopniem usieciowania oraz większą wytrzymałością na rozciąganie niż mieszaniny zawierające tylko termousieciowany CR.The properties of unconventional elastomer blends of crystallizable and thermally crosslinkable chloroprene rubber (CR) with partially hydrogenated (> 95 mol %) acrylonitrile-butadiene rubber (THNBR) were investigated. The blends were prepared by reactive processing combined with dynamic, selective thermal curing of CR and subsequent crosslinking with tetramethylthiuram disulfide (TMTD) and zinc oxide at 433 K. The crosslinking kinetics and tensile mechanical properties of the produced blends were studied. The morphology of blends was investigated using atomic force microscopy (AFM) method and the degree of crosslinking was determined by equilibrium swelling in selected solvents. It has been found that CR/THNBR blends containing 25—45 phr thermally cured CR, subsequently crosslinked with TMTD/ZnO system are characterized by higher crosslinking degree and higher tensile strength than CR/THNBR blends with only thermally cured CR

Nowa metoda sieciowania kauczuku butadienowo-styrenowego za pomocą kwasów Lewisa generowanych in situ

Heating of blends composed of styrene-butadiene rubber (SBR) and chlorosulphonated polyethylene (CSM) at T = 453 K in the presence of fine powdered Zn leads to curing of the elastomers involving interelastomer reactions of the blend components. Analysis of IR spectra leads to the conclusion that the curing in the studied blends is a result of the interelastomer Friedel-Crafts alkylation of the SBR phenyl rings with the elastomeric polyhalide. This reaction is catalyzed with a Lewis acid (ZnCl2) generated in situ by the reaction of CSM with the Zn powder. This new, unconventional method can be used for the curing of the SBR/CSM blends containing selected fillers.Ogrzewanie w T = 453 K mieszanin zawierających kauczuk butadienowo-styrenowy (SBR) i chlorosulfonowany polietylen (CSM) w obecności rozdrobnionego Zn prowadzi do usieciowania składników. Na podstawie widm w podczerwieni (IR) stwierdzono, że sieciowanie składników mieszanki jest wynikiem interelastomerowego alkilowania w reakcji Friedela-Craftsa pierścieni fenylowych makrocząsteczek SBR elastomerycznym polihalogenkiem. Reakcje te są katalizowane kwasem Lewisa (ZnCl2) generowanym in situ w reakcji CSM ze sproszkowanym Zn. Nowa, niekonwencjonalna metoda może być wykorzystana do sieciowania mieszanin SBR/CSM zawierających wybrane napełniacze

Paleomagnetism: continents and oceans

Paleomagnetism is the study of the fossil magnetism in rocks. It has been paramount in determining that the continents have drifted over the surface of the Earth throughout geological time. The fossil magnetism preserved in the ocean floor has demonstrated how continental drift takes place through the process of sea-floor spreading. The methods and techniques used in paleomagnetic studies of continental rocks and of the ocean floor are described and then applied to determining horizontal movements of the Earth''s crust over geological time. An up-to-date review of global paleomagnetic data enables 1000 millionyears of Earth history to be summarized in terms of the drift of the major crustal blocks over the surface of the Earth. The first edition of McElhinny''s book was heralded as a "classic and definitive text." It thoroughly discussed the theory of geomagnetism, the geologicreversals of the Earth''s magnetic field, and the shifting of magnetic poles. In the 25 years since the highly successful first edition of Palaeomagnetism and Plate Tectonics (Cambridge, 1973) the many advances in the concepts, methodology, and insights into paleomagnetism warrant this new treatment. This completely updated and revised edition of Paleomagnetism: Continents and Oceans will be a welcome resource for a broad audience of earth scientists as well as laypeople curious about magnetism, paleogeography, geology, and plate tectonics.Because the book is intended for a wide audience of geologists, geophysicists, and oceanographers, it balances the mathematical and descriptive aspects of each topic.* Details the theory and methodology of rock magnetism, with particular emphasis on intrepreting crustal movements from continental and oceanic measurements* Outlines Earth history for the past 1000 million years, from the Rodinia super-continent through its breakup and the formation of Gondwana to the formation and breakup of Pangea and the amalgamation of Eurasia* Provides a comprehensive treatment of oceanic paleomagnetism* Provides a set of color pateogeographic maps covering the past 250 million years* Written by two internationally recognized experts in the fiel