Nonequilibrium brittle fracture propagation: Steady state, oscillations and intermittency

A minimal model is constructed for two-dimensional fracture propagation. The heterogeneous process zone is presumed to suppress stress relaxation rate, leading to non-quasistatic behavior. Using the Yoffe solution, I construct and solve a dynamical equation for the tip stress. I discuss a generic tip velocity response to local stress and find that noise-free propagation is either at steady state or oscillatory, depending only on one material parameter. Noise gives rise to intermittency and quasi-periodicity. The theory explains the velocity oscillations and the complicated behavior seen in polymeric and amorphous brittle materials. I suggest experimental verifications and new connections between velocity measurements and material properties.Comment: To appear in Phys. Rev. Lett., 6 pages, self-contained TeX file, 3 postscript figures upon request from author at [email protected] or [email protected], http://cnls-www.lanl.gov/homepages/rafi/rafindex.htm

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

New geological and geophysical interpretation of potential fields in the area of Middle Urals transect. Article 2. East of the Urals and Western Siberia

A new 2D model had been built for the geological structure of the Urals and West Siberia along the eastern part of Europrobe seismic reflection profiling in the Urals (ESRU) up to the depth of 15 km. For the first time at the cost of anomalous fields analysis on the parallel profiles applicability of the method was evaluated in the course of density and magnetic susceptibility modeling. The fulfilled studies have confirmed high quality of works of the ESRU’s authors under guidance A.V. Rybalka. Our model makes more concrete ideas on earth crust structure along ESRU. It is shown that actual width of the Platinum Bearing belt is much bigger than shown on geological maps. Into Serov fault zone two meridional ultrabasites plates of different degree of serpentinization were singled out. In the most eastern one according to the model can assume the presence of chromites. The most significant difference of the West Siberia part of ESRU (beginning approximately from 390 km of the model) from more western “Uralian” parts is the bigger “stretching” of entire structures of earth crust. We suppose that this structure stretching and raising of deep metamorphic rocks is a consequence of early Triassic stretching accompanied by forming Triassic systems of West Siberia graben-rifts

A new geological and geophysical interpretation to potential felds near ESRU. The paper 1. Wesern part of the Urals

A new 2D-model of geological structure in the vicinity of Europrobe seismic reflection profiling in the Urals (ESRU) was built to the depth of 15 km. For the first time as a result of analysis of anomalous fields behavior on the parallel profiles in 2D-modeling of density and magnetic properties of the region the applicability of the method was estimated. It was modeled deep seating magnetic body situated under the gravity active layer. Probably this body discontinuing here and there is a continuation of the body revealed in the west part of the Urals Reflection Seismic profile (Urseis). Versions of interpretation of the body were discussed: 1. Block of Precambrian metamorphous rocks with ferruginous quartzite; 2. Block of ocean type rock or mantle diapir (plum). The former is more possible. At the West the upper (up to 3.15-4.8 км depth) part of the section is represented by early Permian terrigenous sediments. Below in the model is a formation (thickness from 0.7 km at the West, up to 1.7 km at the East) of light clastic rocks, below of which situated more dens limestones of middle Paleozoic with thickness from 0.7 km to 1.5 km at the East. The deepest layer of sediment section is constructed from mainly terrigenous thickness of 1.1-1.3 km. The bottom part of the model represents structures of Russian platform basement that moving further to the East submerge under the Ural structures. At 107-125 km along profile the basement intrusion of gabbro-diorite has emerged. From 126 to 142 km along profile one can see a block of terrigenous rocks that probably is a graben of Russian platform. A comparison has been made for blocks of the basement and known ancient metamorphous complexes of the west slope of the Urals (Taratash, etc.). From 169 km along profile one can note falling to the East and broadening with depth highly magnetized body, which probably is serpentinized ultramafic rocks. To this part of the profile Sarany ultramafic intrusion is projected. Ultrabasite zircon age is 1756 ± 12 Ma. Two superimposed stages of zircon formation 464 ± 5 and 439 ± 3 Ma is possibly to be interpreted as age of tectonic ultramafite re-processing. Thus Sarany intrusion probably is the uppest part of the big block situated in 30 km to the West and structurally below Main Ural Deep Faul