Document Type

Thesis

Date of Degree Completion

Summer 2016

Degree Name

Master of Science (MS)

Department

Geological Sciences

Committee Chair

Dr. Lisa Ely

Second Committee Member

Dr. Breanyn MacInnes

Third Committee Member

Dr. Walter Szeliga

Abstract

South-central Chile has an extensive written catalog of historic earthquakes and tsunamis, but such records can be subject to inconsistencies. Dated tsunami deposits are more objective data that provide hard evidence of past tsunamis. The inland extent of deposits from past tsunamis (paleodeposits) can be used in tsunami modeling to reveal characteristics of the source earthquake, but these deposits may have undergone taphonomic processes since initial deposition. Therefore, to determine how tsunami deposits change during burial and preservation and the potential limitations of using paleodeposits in modeling, I investigated the modern 2010 Mw 8.8 Maule earthquake and tsunami as a detailed case study. I used GeoClaw numerical modeling to compare simulated tsunamis from published co-seismic slip distributions of the earthquake with observations from post-tsunami surveys and modified these distributions to determine the most important tsunami-forming characteristics of the earthquake. To investigate taphonomic changes of the deposits, in 2015 I resurveyed the 2010 deposits where they had been previously described and related these findings to modeling results.

The majority of simulated results of the 2010 tsunami underestimated the observed field data, with the most successful simulation created by a published slip distribution that matched observations at 5 of the 6 study sites. My most successful modified slip distribution did not improve this match (4/6 sites), and had an earthquake magnitude that was too large. The errors in modeling derived from using coarse resolution bathymetry and topography were likely the main reason for under-performing simulations, although a combination of other error sources could also play a role.

The tsunami deposits at all study sites were altered by taphonomic processes since 2010, but were still recognizable, indicating moderate preservation. Changes in the deposit inland extent from 2010 - 2015 at two sites ranged from -6% to +24%. Deposit thickness was better preserved than the internal structures, therefore most deposits will likely be preserved in the long-term. Combined, the results of my modeling and sediment studies indicate that GeoClaw modeling based on preserved paleotsunami deposits could provide useful estimates of tsunami-generating earthquake characteristics in south-central Chile, provided better resolution bathymetry and topography are available.

Available for download on Saturday, October 06, 2018

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