Quaternary Rupture Behavior Of The Karakoram Fault And Its Relation To The Dynamics Of The Continental Lithosphere Nw Himalaya West Tibet

Author : Veronica Blythe Prush
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.5/5 (825 download)

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Download or read book Fault Activity and Mechanical Conditions for Rupture of the Akatengneng Shan Earthquake Gate Along the Altyn Tagh Fault, Northwest China written by Veronica Blythe Prush and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Historical rupture mapping and numerical modeling demonstrate that geometric complexities along faults, such as bends and stepovers, act as barriers to earthquake propagation. Numerical models of strike-slip faults suggest that the efficacy of these barriers is dependent on the angle of deviation of fault strike, fault connectivity at depth, rupture directivity, and rupture speed. The efficacy of a barrier to throughgoing rupture, however, may be time-dependent and subject to local stress heterogeneities accumulated by the halting of prior earthquakes within a fault complexity. These factors lead to complexities acting as earthquake gates, which cycle between periods of more or less efficiency as rupture barriers. This fault behavior over many seismic cycles can be constrained using Quaternary records of fault activity. Of particular importance are geomorphic slip rate analyses, which reveal gradients in fault activity that are associated with how ruptures stop within these barriers, and distributed deformation onto secondary structures that accrues as a result of this behavior. Quaternary slip rate gradients require knowledge of 1) total displacement of an offset landform and 2) a minimally ambiguous relationship between timing of displacement and landform formation. This dissertation contributes to uncertainty estimates in both displacement measurements and age estimation methods commonly used for Quaternary slip rate analyses. The appendix of this dissertation includes a principal component analysis for determining two or three-dimensional piercing line offset. This method quantifies uncertainty in piercing line extrapolation, reducing uncertainty estimates and providing more rigorous fault activity constraints. In Chapter 1 I present a mechanistic model for cosmogenic nuclide inheritance that incorporates the contributions of episodic landsliding and background erosion due to soil formation. Inheritance-corrected landform ages are systematically younger than published ages. Application of the model provides a rigorous approach to correcting landform ages for inheritance and reveals information on landslide frequency, with broad implications for hazard and land use. These methods represent a significant advance in slip rate measurements, and I utilize both throughout my dissertation. The sinistral Altyn Tagh fault (ATF) in northwest China is one of the primary structures accommodating deformation of the Tibetan Plateau due to ongoing Indian-Eurasian Plate convergence. Along its central ~800 km span are four fault complexities that may act as rupture barriers. Paleoseismic records, slip-per-event analyses, and numerical models suggest that one of these complexities, the Akatengneng Shan (AS), acts as an earthquake gate to rupture along the central portion of the ATF. Fault geometry is complex within the Akatengneng Shan, and includes an eastern releasing stepover, central double restraining bend, and western releasing double bend. This dissertation seeks to determine the efficacy of the Akatengneng Shan earthquake gate as a barrier to rupture by evaluating Quaternary fault slip rate at 7 sites along the main ATF fault strand and secondary structures. I find that the pattern of slip distribution within the AS is complex and varies with location in the range. Slip rate is found to decline from 8 - 12 mm/yr on the Xorkoli section of the ATF to 4.7 ± 0.8 mm/yr on the eastern Pingding section, suggesting half of the net ATF slip rate is distributed to other structures within the region at this longitude (Chapter 2). In Chapter 3 I demonstrate this by documenting slip rates through the eastern side of the range that in sum account for approximately two-thirds of total Altyn Tagh fault slip. I further show that deformation must be significantly more diffuse on the western side of the AS, where the sole morphologically prominent Quaternary active fault carries less than a third of the total expected slip rate. This result highlights the importance of secondary structures in accommodating deformation within earthquake gate systems, and that much of this deformation may be highly distributed and not easy to quantify on mapped faults. To determine the mechanical conditions under which rupture propagates through the complex fault geometry of the AS, I use forward modeling of applied stress fields on a simplified fault geometry of the AS to determine their kinematic compatibility with field observations of fault slip direction. I show that there is no single stress field that can allow for the observed slip vectors on all active faults within the Akatengneng Shan earthquake gate. I find instead that there must be rotation of the stress field near the fault to allow for sinistral slip along its more misoriented sections. Stress rotation could be accommodated by elevated pore pressure or a weakened fault core relative to a stronger surrounding crustal volume, as has been argued along other mature continental strike-slip faults, such as the San Andreas fault. Evaluating earthquake gate-like rupture behavior should account for the orientation, kinematics, and rate of activity of secondary structures that accommodate deformation away from the main fault, as this off-fault deformation provides useful information for understanding throughgoing rupture, as well as alternative pathways for gate-breaching events.