Date of Award

12-17-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

First Advisor

Haydar Al-Shukri

Abstract

Damaging earthquakes including pre-historical, historical and recent demand paleoseismic studies to improve seismic risk assessment of future destructive earthquakes. Such large earthquakes could damage many structures, kill scores of people and leave others homeless, and devastate the economy. In this study, extensive research efforts are described to investigate the feasibility and effectiveness of using Ground Penetrating Radar (GPR) in detecting and identifying specific geological features that are related to historic and prehistoric earthquakes. These features are preserved in the near surface soil and manifested as sand blows, buried paleo-surfaces, venting dikes, and structural faults. They are related to severe cyclic shaking of saturated loose sand to that resulted in grain rearrangement and an increase in pore pressure due to the overburden soil. The liquefied sand usually vented through breaches in the soil generating sand dikes. In addition to geophysical fieldwork and data acquisition, the research integrates multiple distinct approaches including analyzing satellite and areal images, soil conditions, trenching and logging, and AMS radiocarbon dating and optically-stimulated luminescence(OSL) dating. The target area of this study is south and west of Marianna, Arkansas USA. Image Analysis integrated with Geographic Information System (GIS) tools was used to assist in selection of the five sites studied for this project. Because the sand units were relatively thin, a GPR system equipped with a 400-MHz antenna, a survey cart and survey wheel was employed to identify the suitable locations for trenching areas. Four trenches were excavated in the study area, two each at site 3 (DBNW3) and site 5 (DBNW5). The north walls of three trenches were logged and sampled for dating the sand blow features. Investigations of sand blows in the Marianna area indicate that these features were formed prior to 4800 years ago. The long axes of many of these sand blows are oriented SE-NW, most likely a representation of a SE-NW lineament above a dormant fault that was active in the past. Liquefaction analyses indicate that an earthquake with at least a magnitude of 6 is needed to produce such liquefaction features. However, caution is recommended prior to estimating the magnitudes because there are many factors affecting the formation of sand blows.

Download

Share

COinS