scholarly journals Transient Brittle‐Ductile Transition Depth Induced by Moderate‐Large Earthquakes in Southern and Baja California

2019 ◽  
Vol 46 (20) ◽  
pp. 11109-11117 ◽  
Author(s):  
Yifang Cheng ◽  
Yehuda Ben‐Zion
Keyword(s):  
Baja California ◽  
Brittle Ductile Transition ◽  
Transition Depth ◽  
Large Earthquakes

scholarly journals Dynamics of interplate domain in subduction zones: influence of rheological parameters and subducting plate age

2012 ◽  
Vol 4 (2) ◽  
pp. 943-992
Author(s):  
D. Arcay
Keyword(s):  
Subduction Zones ◽  
Activation Volume ◽  
Rheological Parameters ◽  
Strength Increase ◽  
Thermomechanical Model ◽  
Mantle Viscosity ◽  
Brittle Ductile Transition ◽  
Transition Depth ◽  
Subducting Plate

Abstract. The properties of the subduction interplate domain are likely to affect not only the seismogenic potential of the subduction area but also the overall subduction process, as it influences its viability. Numerical simulations are performed to model the long-term equilibrium state of the subduction interplate when the diving lithosphere interacts with both the overriding plate and the surrounding convective mantle. The thermomechanical model combines a non-Newtonian viscous rheology and a pseudo-brittle rheology. Rock strength here depends on depth, temperature and stress, for both oceanic crust and mantle rocks. I study the evolution through time of, on one hand, the kinematic decoupling depth, zdec and, on the other hand, of the brittle-ductile transition (BDT) depth, zBDT, simulated along the subduction interplate. The results reveal that zBDT mainly depends on the friction coefficient characterising the interplate channel and on the viscosity at the lithosphere-asthenosphere boundary. The influence of the weak material activation energy is of second order but not negligible. zBDT becomes dependent on the ductile strength increase with depth (activation volume) if the BDT occurs at the interplate deocupling depth. Regarding the interplate decoupling depth, it is basically a function of (1) mantle viscosity at asthenospheric wedge tip, (2) difference in mantle and interplate activation anergy, and (3) activation volume. Specific conditions yielding zBDT = zdec are discussed. I then present how the subducting lithosphere age affects the brittle-ductile transition depth and the kinematic decoupling depth in this model. Simulations show that a rheological model in which the respective activation energies of mantle and interplate material are too close impedes strain localization during incipient subduction of a young (20 Myr old) and soft lithosphere under a thick upper plate. Finally, both the BDT depth and the decoupling depth are a function of the subducting plate age, but are not influenced in the same fashion: cool and old subducting plates deepen the BDT but shallow the interplate decoupling depth. Even if BDT and kinematic decoupling are instrinsically related to different mechanisms of deformation, this work shows that they are able to interact closely.

scholarly journals Dynamics of interplate domain in subduction zones: influence of rheological parameters and subducting plate age

Solid Earth ◽  
2012 ◽  
Vol 3 (2) ◽  
pp. 467-488 ◽  
Author(s):  
D. Arcay
Keyword(s):  
Activation Energy ◽  
Subduction Zones ◽  
Activation Volume ◽  
Viscosity Reduction ◽  
Rheological Parameters ◽  
Strength Increase ◽  
Thermomechanical Model ◽  
Brittle Ductile Transition ◽  
Transition Depth ◽  
Subducting Plate

Abstract. The properties of the subduction interplate domain are likely to affect not only the seismogenic potential of the subduction area but also the overall subduction process, as it influences its viability. Numerical simulations are performed to model the long-term equilibrium state of the subduction interplate when the diving lithosphere interacts with both the overriding plate and the surrounding convective mantle. The thermomechanical model combines a non-Newtonian viscous rheology and a pseudo-brittle rheology. Rock strength here depends on depth, temperature and stress, for both oceanic crust and mantle rocks. I study the evolution through time of, on one hand, the brittle-ductile transition (BDT) depth, zBDT, and, on the other hand, of the kinematic decoupling depth, zdec, simulated along the subduction interplate. The results show that both a high friction and a low ductile strength at the asthenospheric wedge tip shallow zBDT. The influence of the weak material activation energy is of second order but not negligible. zBDT becomes dependent on the ductile strength increase with depth (activation volume) if the BDT occurs at the interplate decoupling depth. Regarding the interplate decoupling depth, it is shallowed (1) significantly if mantle viscosity at asthenospheric wedge tip is low, (2) if the difference in mantle and interplate activation energy is weak, and (3) if the activation volume is increased. Very low friction coefficients and/or low asthenospheric viscosities promote zBDT = zdec. I then present how the subducting lithosphere age affects the brittle-ductile transition depth and the kinematic decoupling depth in this model. Simulations show that a rheological model in which the respective activation energies of mantle and interplate material are too close hinders the mechanical decoupling at the down-dip extent of the interplate, and eventually jams the subduction process during incipient subduction of a young (20-Myr-old) and soft lithosphere under a thick upper plate. Finally, both the BDT depth and the decoupling depth are a function of the subducting plate age, but are not influenced in the same fashion: cool and old subducting plates deepen the BDT but shallow the interplate decoupling depth. Even if BDT and kinematic decoupling are intrinsically related to different mechanisms of deformation, this work shows that they are able to interact closely. Comparison between modelling results and observations suggests a minimum friction coefficient of 0.045 for the interplate plane, even 0.069 in some cases, to model realistic BDT depths. The modelled zdec is a bit deeper than suggested by geophysical observations. Eventually, the better way to improve the adjustment to observations may rely on a moderate to strong asthenosphere viscosity reduction in the metasomatised mantle wedge.

Health and Health Care Problems Among the Kumiai of San Antonio Necua and Their Indigenous Relatives in Baja California

2003 ◽  
Vol 1 (1) ◽  
pp. 140-157 ◽  
Author(s):  
K. Jill Fleuriet
Keyword(s):  
Health Care ◽  
Baja California ◽  
San Antonio ◽  
Rural Poverty ◽  
Indigenous Communities ◽  
Traditional Healers ◽  
Medical Pluralism ◽  
Indigenous Groups ◽  
Health And Illness ◽  
Care Problems

The rural Kumiai community of San Antonio Necua is one of the few remaining indigenous communities in Baja California, Mexico. Necuan health and health care problems are best understood through a consideration of the effects of colonialism and marginalization on indigenous groups in northern Baja California as well as a tradition of medical pluralism in Mexico. The lack of traditional healers and biomedical providers in the community, high rates of preventable or manageable illnesses, and a blend of biomedical, folk mestizo, and traditional indigenous beliefs about health and illness reflect current conditions of rural poverty and economic isolation. Descriptions of health and health care problems are based on ethnographic fieldwork among the Kumiai, their Paipai relatives, and their primary nongovernmental aid organization.

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