Browsing by Author "Chen, PC"

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    Deformation textures in the principal slip zone of the Chelungpu fault, Taiwan, and its implication for stress change during the seismic cycle
    (American Geophysical Union, 2018-12-10) Kuo, LW; Luzin, V; Chen, PC; Yeh, EC; Ma, KF
    Thermal pressurization is postulated for fault lubrication during seismic ruptures and leads catastrophic natural disasters. One recent example includes the active Chelungpu fault resulted in 1999 Mw 7.6 Chi-Chi earthquake in Taiwan. Efforts to improve seismic hazard assessment in such a region require a quantitative understanding of fault dynamics during earthquake generation. The principal slip zone (PSZ) of the active Chelungpu fault, showing rapid shear heating of fault gouge, might preserve stress magnitude accommodated the thermal pressurization during the earthquake. Here we conduct in situ neutron texture analysis for determining both recent and ancient histories of rocks because deformation events like earthquakes are imprinted in the crystallographic grain orientation. Overall, 12 samples collected from the fresh fault core, which represent almost continuous scan across the fault, were analyzed with the neutron experiment on KOWARI, Australia. Two distinguished types of the preferred orientation were found: (1) the textures with c-axis orientations predominantly parallel to bedding planes, which are found in the most of sedimentary rocks, are compaction-related and this is observed for the most analyzed samples; (2) the textures of sample 5 and 10, which are identified as Chi-Chi PSZ, demonstrate quite different deformation history with different orientation of the principal stresses that plausibly resulted from thermal pressurization process within the PSZ. Integrating these observations with the multiple stress inversion method, we obtain the change in stress field and it magnitude related to the end of the fault rupture. Since thermal pressurization process is proposed as a widespread process for earthquake generation and propagation, we suggest that the investigation of gouge orientation of a fault offers the opportunity to study the stress drop and recovery during the seismic cycle.
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    Pore domain outer helix contributes to both activation and inactivation of the hERG K+ channel
    (American Society for Biochemistry and Molecular Biology, 2009-01-09) Ju, P; Pages, G; Riek, RP; Chen, PC; Torres, AM; Bansal, PS; Kuyucak, S; Kuchel, PW; Vandenberg, JI
    Ion flow in many voltage-gated K+ channels (VGK), including the (human ether-a-go-go-related gene) hERG channel, is regulated by reversible collapse of the selectivity filter. hERG channels, however, exhibit low sequence homology to other VGKs, particularly in the outer pore helix (S5) domain, and we hypothesize that this contributes to the unique activation and inactivation kinetics in hERG K+ channels that are so important for cardiac electrical activity. The S5 domain in hERG identified by NMR spectroscopy closely corresponded to the segment predicted by bioinformatics analysis of 676 members of the VGK superfamily. Mutations to approximately every third residue, from Phe(551) to Trp(563), affected steady state activation, whereas mutations to approximately every third residue on an adjacent face and spanning the entire S5 segment perturbed inactivation, suggesting that the whole span of S5 experiences a rearrangement associated with inactivation. We refined a homology model of the hERG pore domain using constraints from the mutagenesis data with residues affecting inactivation pointing in toward S6. In this model the three residues with maximum impact on activation (W563A, F559A, and F551A) face out toward the voltage sensor. In addition, the residues that when mutated to alanine, or from alanine to valine, that did not express (Ala(561), His(562), Ala(565), Trp(568), and Ile(571)), all point toward the pore helix and contribute to close hydrophobic packing in this region of the channel. © 2009, American Society for Biochemistry and Molecular Biology