Our research focus lies in understanding the processes associated with deformation of the continental lithosphere, and is firmly grounded in remote sensing and the acquisition of field-based observational data. The integration of field observations, cosmogenic dating, remote sensing, and space geodesy to quantify fault system behavior over various time scales comprises the core of my research. PhD research has focused on the Himalaya-Karakoram-Tibet collision zone and addresses four highly debated topics regarding the deformation of continents: 1) The relationship between the present day and ancient kinematics of the Tibetan orogen, 2) testing models of intracontinental deformation: microplate vs. thin-viscous sheet, 3) The function of strike-slip faulting during orogenesis, and 4) the mechanics of conjugate strike-slip faults.

Geometry and kinematics of conjugate faults in central Tibet

How does the Tibetan plateau accommodate the Indo-Asian collision? Previous research has emphasized Tibet’s margins, such as the Himalayan fold-thrust belt, and the Red River and Altyn Tagh strike-slip faults, which are believed to contribute to rigid block extrusion of intact continental terranes. Using an integrative approach, we use field observations and remote sensing to understand a series of previously unidentified conjugate strike-slip faults within central Tibet. The conjugate strike-slip structures accommodate a significant portion of Indo-Asian convergence, and have led to the development of a new tectonic model, which places emphasis on the distributed eastward extrusion of a series of crustal wedges. The wedges are bounded by a system of intersecting NE and NW-striking strike-slip faults. In turn, the conjugate fault geometry requires coeval fault initiation and fault slip (over geologic time scales), and is consistent with an eastward spreading of the Tibetan crust. The kinematics of the conjugate fault systems is consistent with the bedrock geology, earthquake focal mechanisms, and geodetic observations from east central Tibet.

Surface deformation in central Tibet using InSAR

A goal of understanding continental tectonics is to quantify the rate of fault slip and the degree to which adjacent faults interact. Using InSAR, we have constructed continuous maps of the surface displacement in the vicinity of the conjugate strike-slip faults in central Tibet. Our data indicates that the conjugate fault systems account for ~5% of present-day India-Siberia convergence. In terms of fault kinematics, we find that while one segment of the conjugate fault system is accumulating elastic strain, its opposing conjugate does not appear to do so within the time span of the interferograms and the detection limit of InSAR. These results are being used to infer the mechanical properties of the crust, in terms of the stability of conjugate strike-slip faults. In addition, our results provide the far-field geodetic fault slip rates to quantify the distribution of instantaneous strain throughout the collision zone.

Mechanics of conjugate strike-slip faults

The acute intersection angle for conjugate strike-slip faults in central Tibet is ~70°, and is bisected by the axis of maximum extension. Individual strike-slip structures in general, exceed 250 km length, and exhibit <20 km of fault slip in most cases. The observation of the fault geometries and kinematics is inconsistent with conventional theories of faulting, in that the acute angle is not bisected by the principle shortening direction. We suggest that strike-slip faults in central Tibet initiated at, or near their present day geometry in a two-stage process through stress transfer between contrasting rheologic crustal layers. In this kinematic model, the conjugate strike-slip faults initiate in the middle crust with an intersection angle of ~90°, as predicted by plasticity theory. As deformation proceeds, the conjugate strike-slip shear zones and surrounding rock mass rotate about vertical axes to their ~present day geometry. During the second stage, faulting initiates in the upper crust through stress transfer. Vertical-axis rotation of upper crustal blocks is not required in this mode of faulting, and may explain why small intersection angles are often found to occur between conjugate strike-slip faults where evidence of vertical-axis rotations are lacking. Our conceptual model implies that bottom-driven processes are significant factors to consider when describing orogenic belts. Moreover, this particular conjugate strike-slip configuration is not an isolated case, but rather, is characteristic of the entire Alpine-Himalayan-Tibet orogenic belt, and the western United States.

Herat and Chaman strike-slip faults, Afghanistan

A geologically unexplored region that lies between Tibet and Iran is Afghanistan. This region exhibits an apparent example of strike-slip tectonics that is related to the Arabia-Indo-Eurasian collision. However, fundamental questions in terms of the fault geometry, kinematics, and slip-rates along the prominent fault systems are unknown. I will initiate a remote sensing project that involves understanding the fault kinematics of the Herat and Chaman strike-slip faults. Recent advances in remote sensing will provide a means to understand the structural framework of the region, and to identify potential targets for future field-based investigations (e.g., cosmogenic dating). I propose an integrated study using available remote sensing imagery to characterize the regional fault geometry (e.g., ASTER, SRTM, and Quick Bird).

Denali fault, Alaska

The 2002 Denali earthquake rupture initiated on the Susitna Glacier thrust, and evolved into an essentially purely right-lateral strike slip earthquake (Mw = 7.9). The right-slip Denali fault strikes NW, accommodates dominantly horizontal motion, and is relatively discrete along its SE segment. To the north, the fault changes to an ~W-striking orientation and feeds slip into a series of N-directed thrusts and fault propagation folds. The degree of along-strike slip-partitioning between the strike-slip fault segment and its associated off fault structures (e.g. fault propagation folds), and fault slip rates are unknown. Two N-S GPS transects span the Denali fault, and a catalogue of relocated earthquakes can provide a means to estimate both the geodetic and seismic strain rates. However, a self-consistent study that integrates both neotectonic field observations and the available geophysical data into a coherent kinematic picture is presently lacking. I propose to expand upon the observational data collected from the Denali fault system, by exploring the theoretical aspects of earthquake nulcleation, slip partioning, and their implications for lithospheric deformation.

 

 

 




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