Years participated in RESESS:
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Major: Mathematics; Geological Science minor
Academic Affiliation: Boston College
Research Mentors: David Phillips and Christine Puskas
Writing Mentor: Lesley Ann Butcher
A spark from a gifted, passionate high school earth science teacher was the catalyst for New Yorker Brian Chung, an enthusiastic mathematics student with a particular love of the outdoors and cross country running, to pursue an undergraduate education at Boston College connecting mathematics with geophysics. Additional liberal arts interests of the violin and Eastern European linguistics have led Brian to seek opportunities in applying his technical abilities in areas of social significance. At RESESS, Brian conducted computational research in stress evolution and earthquake triggering related to the 1983 Borah Peak earthquake in central Idaho, and has connected his findings to physical manifestations by way of an extensive field trip to the region. His techniques draw on distinguished studies in such areas as southern California and are directly applicable to countless regions in conducting risk analysis for seismic events.
The M7.3 1983 Borah Peak earthquake occurred along the Lost River fault and was the largest historic earthquake in Idaho. The Lost River fault is one of several large normal faults in the central Intermountain Seismic Belt. The stress evolution of this family of faults, including the Lost River, Lemhi, Beaverhead, and Sawtooth, is analyzed by computing Coulomb stress changes from paleoearthquakes and interseismic loading. The event can be understood with respect to prehistoric stress interactions between the brittle and creeping segments of the central Idaho fault system. Paleoseismic dates, offsets, and slip rates are acquired from published scarp and trench analyses. Coulomb stress change models are based on coseismic earthquake offsets in the upper seismogenic crust and on cumulative slip from fault creep in the lower crust. Models of Coulomb stress change are based on known current fault geometry and inferred geometry from the Borah Peak event. The time-lapse models commence at 9.5 ka. Mean dates and slip rates are used in a preliminary model in light of large age ranges on the order of thousands of years. Coulomb stresses from creeping segments are modeled as slipping fault planes from the brittle-ductile boundary down to the crust- mantle boundary. The Borah Peak earthquake and most paleoearthquakes occurred in regions of increased Coulomb stress of up to 5 bars. These stress changes are dominantly dictated by single-segment coseismic displacements rather than interseismic loading in this preliminary model. Coseismic stress drops on a segment are about 5 bars, while interseismic loading contributes to approximately 2-bar Coulomb stress increases in the overriding brittle lithosphere of the same segment. Coulomb stress increases from adjacent segment earthquakes are approximately 4 bars. Both the isolated Borah Peak model and the total stress model are consistent with the distribution of post-Borah Peak earthquakes north of the Lost River fault. Additional models will be run to consider varying paleoearthquake dates and interseismic slip rates to see how sensitive Coulomb stress changes are to these parameters. Interseismic loading displacements will also be compared to GPS velocities to check fault slip rates.