Brugia Malayi - Clark Science Center - Smith College

Analyzing Systems of Earthquake-Related Landform Deformation along
the Chilean Coastline
Paula Burgi and Alexandria Julius
A large subduction zone is present along Chile’s Pacific coastline, where the Nazca plate is subducting under the South American
plate. Stress induced on the upper South American plate by the lower Nazca plate causes differing physical expressions on the
upper plate. In Southern Chile, the deformation takes the form of faults, which is expected in this tectonic setting. In Northern
Chile, however, there is less large-scale faulting but rather, relatively small cracks in the ground. Our goal was to examine the
different manifestations of stress and their origins. Factors for this discrepancy are the subduction zone geometry changing with
geographic location, and variation of locking between the subduction zone and the upper plate, determining how much the lower
plate slips relative to the upper plate.
Our main tool of analysis was mathematical modeling using MATLAB, a technical computing software program. Initially,
we created an accurate 3-dimensional representation, in the form of a triangular mesh, of the subduction zone and the upper
plate faults. Next, we calculated the partial derivatives of displacement and strain 1 imposed on the upper plate faults by the rate
of subduction of the lower plate. With this information, we were able to calculate the stress imposed on the faults. We were also
able to calculate slip along the faults by using the computed stress on the faults, and inverting the partial derivative calculations.
After determining the stresses on the upper plate faults, we statistically modeled the distribution of stresses in relation to
geographical location. Figure 1 is a histogram of the three components of stress in Northern Chile versus Southern Chile. There
is no significant variation in the distribution of stress between Northern and Southern Chile. Figure 2 represents the distribution
of slip along the upper plate faults. The calculated slip, which would result from 150 years’ worth of subduction zone locking,
yields slip rates consistent with previous data. 2
The consistency of stress between Northern and Southern Chile signifies that there may be other determining factors for
the discrepancy in stress expression. Possible explanations may be the influence from areas of the subduction zone that were not
included in our calculations, and geographic differences in rock rigidity, earthquake size and frequency, and occurrences of ancient
structures. The results shown in Figure 2 indicate that our model estimates slip rates on faults along the Chilean coastline that are
consistent with geologic studies. (Supported by the Jack Loveless Startup Fund)
Advisor: Jack Loveless
References:
1
Meade, BJ. 2007. Algorithms for the Calculation of Exact Displacements, Strains, and Stresses for Triangular Dislocation Elements in a Uniform Elastic Half Space.
Computers & Geosciences 33.8: 1064-1075.
2
Allmendinger, R. W., and G. González. 2010. Neogene to Quaternary Tectonics of the Coastal Cordillera, Northern Chile. Journal of Tectonophysics 495: 93-110.
Moreno, M., D. Melnick, M. Rosenau, J. Baez, J. Koltz, O. Oncken, A. Tassara, J. Chen, K. Bataille, M. Bevis, A. Socquet, J. Bolte, C. Vigny, B. Brooks, I. Ryder, V.
Grund, B. Smalley, D. Carrizo, M. Bartsch, and H. Hase. 3 Feb 2012. Towards Understanding Tectonic Control on the Mw 8.8 Maule Chile Earthquake. Earth and
Planetary Science Letters 321-322: 152:165.
Chlieh, M., H. Perfettini, H. Tavera, J. Avouac, D. Remy, J. Nocquet, F. Rolandone, F. Bondoux, G. Gabalda, and S. Bonvalot. Oct. 2010. Interseismic Coupling and
Seismic Potential along the Central Andes Subduction Zone.” American Geophysical Union, Vol 116.
2012
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