Abstract
Several studies have shown that the asymmetric geometry of thrust faults
with respect to the Earth's surface leads to a complex dynamic behavior
of updip ruptures, such as asymmetric ground motions and temporal
variations in normal stress. Here we use an experimental set-up designed
to mimic earthquakes on thrust faults to study how fully developed updip
ruptures interact with the free surface. The experimental technique
(Rubino et al., 2017) combines ultra-high speed photography and digital
image correlation and enables to produce coherent full-field maps of
dynamic displacements, velocities, strains, and stresses associated with
the ruptures at intervals of one microsecond. The ruptures typically
arrive to the free surface at a supershear rupture speed and include a
second phase of a trailing Rayleigh disturbance. Both phases involve a
temporal increase in velocity magnitude. The full-field experimental
measurements visualize how the free surface breaks the symmetry in the
velocity field as the rupture arrives, with a larger peak of velocity
magnitude in the hanging-wall compared to that in the footwall.
Moreover, while the arrival of the rupture is associated with a
fault-parallel motion, as slip continues, the motion of the hanging wall
becomes sub-vertical and the motion of the footwall includes a large
horizontal component. This study provides the first experimental
measurements of the stresses associated with the rupture near the free
surface. The measurements show small initial increase in normal stress
as the rupture breaks the free surface followed by a significant
reduction. Additional reduction is observed at the arrival of the
trailing Rayleigh rupture, with a temporal complete release in
experiments that were conducted under small initial compressive load
(indicating possible opening of the interface). All experiments show a
significant delay in the response of shear resistance to the variations
in normal stress.
Original language | English |
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Title of host publication | American Geophysical Union, Fall Meeting 2019 |
State | Published - Dec 2019 |
Keywords
- 7209 Earthquake dynamics
- SEISMOLOGY
- 7215 Earthquake source observations
- 7230 Seismicity and tectonics
- 7290 Computational seismology