618403 event 1551113360 1551113360 COLLEGE OF SCIENCES
SCHOOL OF EARTH AND
ATMOSPHERIC SCIENCES
EAS Ph.D. Defense
Tiegan Hobbs
March 8,
2019
3:00 PM
Earth and Atmospheric Sciences
Ford Environmental Science &
Technology (ES&T)
311 Ferst Drive, ES&T
Atlanta, GA 30332-0340
Web: eas.gatech.edu
ES&T
L1255
Title: Postseismic Response Following the 2012 Mw 7.6 Nicoya, Costa Rica
Earthquake
Committee members: Dr. Andrew Newman (Advisor), Dr. Zhigang Peng,
Dr. J. David Frost, Dr. Marino Protti, Dr. Timothy Dixon
Abstract: Characterization of the surface deformation related to the 2012
moment magnitude (Mw) 7.6 Nicoya earthquake was undertaken using
continuous and campaign Global Positioning System (GPS) observations. This
location is uniquely situated to monitor megathrust conditions as the peninsula
extends to within 60 km of the trench. The entirety of the postseismic and
relocking period were considered, totaling 5 years. Seismic observations were
also included, to cumulatively elucidate the timing and spatial extent of
megathrust behavior. Afterslip with equivalent Mw of 7.5 was shown to exist in
patches that were distinct from aftershocks, both of which were most abundant
immediately updip of the coseismic rupture patch. This was an important, albeit
failed, test of the applicability of using repeating aftershocks as a proxy for slip.
As trench-normal afterslip waned, relocking was initiated but shortly interrupted
by a period of exclusively trench-parallel motion across the Nicoya forearc. This
was a novel observation. Combined with results of a backslip inversion, these
findings suggest that slip partitioning may be controlled by megathrust coupling.
By 2016 the surface velocities returned to preseismic levels, indicating a return
to stable interseismic conditions. These results, and their impact on active
tectonics and subduction physics, are discussed.

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