Publication Date

2018-07-24

Availability

Embargoed

Embargo Period

2020-07-23

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Marine Geology and Geophysics (Marine)

Date of Defense

2018-04-20

First Committee Member

Falk C. Amelung

Second Committee Member

Shimon Wdowinski

Third Committee Member

Guoqing Lin

Fourth Committee Member

Timothy Dixon

Fifth Committee Member

Enrique Cabral-Cano

Abstract

Mexico City, located in central Mexico, is one of the largest and most populated urban areas in the world. Due to its geographic location and particular geological conditions, the city and its population has been exposed to geological hazards. On the one hand, the city is exposed to earthquakes due to ongoing seismic activity originated offshore the southern coast of Mexico, mainly along the convergence boundary between the North American and the Cocos plates. On the other hand, the city was built on a highly compressible lacustrine sediment sequence, which has historically produced seismic amplification. Additionally, and triggered by aggressive groundwater extraction, the sedimentary sequence is subjected to differential land subsidence with rates exceeding 350 mm/yr. The city-scale subsidence patterns and rates were investigated since the 1940’s using multiple geodetic techniques, including the more advanced Interferometric Synthetic Aperture Radar (InSAR). However, these studies focused on the city-scale land subsidence and mostly ignored important differential displacements occurring at smaller scales, which cause damage to buildings and infrastructure. In this work, I use InSAR observation to evaluate geological hazards in Mexico City, focusing on smaller-scale signals typically hidden by the first-order subsidence that cause damage to buildings and infrastructure. First, I use InSAR to systematically measure the subsidence rates along the city’s Metro system, and evaluate the differential subsidence by the means of a 1D parameter—velocity gradient. My results yield that gradient values along some of the Metro lines exceed rates of 1x10^(-3) yr^(-1); these segments of high velocity gradients are also known to suffer from damage or malfunctioning, as reported by official and unofficial sources. Second, I use a band-pass filtering method to decompose the city’s InSAR-derived velocity map into maps of long, intermediate, and short wavelength subsidence velocities. In this study, I focus on the intermediate wavelength signal, which reflect shallow subsidence of large buildings and infrastructure facilities, as Metro lines, and can be used for infrastructure monitoring and improving geotechnical zone boundaries. Third, I use InSAR products to study an atypical phenomenon of shallow faulting induced by the September 19th, 2017 Puebla-Morelos earthquake. The induced shallow faults occur in areas that experienced differential subsidence and shallow faulting and, hence, represent a rapid occurrence of a slow faulting process that typically last 10-20 years of slow faulting.

Keywords

InSAR; geological hazards; subsidence; differential subsidence; Mexico City; metro

Available for download on Thursday, July 23, 2020

Share

COinS