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Titolo:
Finite element models of stress orientations in well-developed strike-slipfault zones: Implications for the distribution of lower crustal strain
Autore:
Lynch, JC; Richards, MA;
Indirizzi:
Univ Calif Berkeley, Dept Earth & Planetary Sci, Berkeley, CA 94720 USA Univ Calif Berkeley Berkeley CA USA 94720 ary Sci, Berkeley, CA 94720 USA
Titolo Testata:
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
fascicolo: B11, volume: 106, anno: 2001,
pagine: 26707 - 26729
SICI:
0148-0227(20011110)106:B11<26707:FEMOSO>2.0.ZU;2-T
Fonte:
ISI
Lingua:
ENG
Soggetto:
SAN-ANDREAS FAULT; EARTHQUAKE CYCLES; CALIFORNIA; FRICTION; STATE; EVOLUTION; MOTION; SYSTEM; DEPTH;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
40
Recensione:
Indirizzi per estratti:
Indirizzo: Lynch, JC Univ Calif Berkeley, Dept Earth & Planetary Sci, Berkeley, CA 94720 USA Univ Calif Berkeley Berkeley CA USA 94720 erkeley, CA 94720 USA
Citazione:
J.C. Lynch e M.A. Richards, "Finite element models of stress orientations in well-developed strike-slipfault zones: Implications for the distribution of lower crustal strain", J GEO R-SOL, 106(B11), 2001, pp. 26707-26729

Abstract

Finite element models are used to examine the effects of strike-slip earthquakes on stresses in an elastic layer overlying a finite width viscoelastic shear zone in the lower crust. The overall dimensions of the model are 300 km wide, 400 km long, and 50 km deep. Three geometries for the lower crustal shear zone are considered: (1) a viscoelastic half-space approximation,with a shear zone that extends to the model boundaries (300 km in width); (2) a wide shear zone model (70 km in width); and (3) a narrow shear zone model (10 km in width). Earthquakes are simulated with a fault plane that slips without friction at the desired time step and is centered above the shear zone, extending to a depth of 15 km and running the length of the mesh. Far-field plate velocity boundary conditions are enforced at the model edges so that stress on the fault evolves naturally. A Coulomb-type failure criterion based on the average shear stress on the fault is set such that the earthquake cycle is similar to 250 years. The models are run until a limit cycle is reached and transient stresses have decayed away. We focus on the maximum changes in the stress field during the earthquake cycle by examining stresses before and immediately after each earthquake. In addition to comparisons of the separate components of the stress tensor we present resultsin the form of maximum compressive stress orientations, plunge angles of the principal stress axes, and beach ball diagrams that facilitate visualizing the full tensor. Stresses are concentrated in the upper crust where it overlies the finite width viscoelastic shear zone, which causes the plunge angles of the principal stress axes to rotate from Andersonian orientations of 90 degrees and 0 degrees to angles that approach 45 degrees in the lowercrust. Our results suggest that an examination of stress orientations in the upper and middle crust from borehole breakouts and focal mechanisms may provide insight as to the distribution of strain in the lower crust and mayeventually allow us to distinguish between localized and distributed deformation models for the lower crust in active strike-slip zones.

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Documento generato il 18/01/20 alle ore 21:30:34