Geophysics and Seismology Commons^™

Mitigating Non-Linearity In Full Waveform Inversion Using Scaled-Sobolev Norms, Mohammad Akbar Hosain Zuberi

Electronic Thesis and Dissertation Repository

Seismic full waveform inversion (FWI) is a non-linear problem. The Born approximation provides a way to linearize FWI and obtain a gradient in a computationally efficient manner. However, this linearization is only valid if the background velocity is sufficiently known, which often is not possible in practice. There have been various attempts at solving problems associated with the non-linearity of FWI by separating the problems of background and scatterer inversion. Most of the methods, however either depend on the availability of low frequencies and large offsets in the data, or separate the spatial scales completely, which removes the scattered information …

Investigating The Mechanism Of Deep-Focus Earthquakes Via In-Situ Acoustic Emission Experiments On Fe2sio4 At High Temperature And Pressure, Timothy Officer

Electronic Thesis and Dissertation Repository

In subduction zones, earthquakes are thought to be associated with faulting that arises from phase transformations. In order to test the viability of this mechanism experimentally, it was necessary to make microseismic measurements while the mineral under investigation was subjected to the pressure and temperature (P,T) conditions corresponding to their environment at depth. A system has been developed capable of making in situ acoustic emission (AE) measurements on samples under P,T conditions representative of the upper mantle and transition zone. Experiments were performed in a 3000-ton multi-anvil press using an 18/11 octahedral cell with 6 piezoelectric transducers mounted on the …

Time Series Analysis Of Surface Deformation Associated With Fluid Injection And Induced Seismicity In Timpson, Texas Using Dinsar Methods, Simon Thorpe

Electronic Thesis and Dissertation Repository

In recent years, a rise in unconventional oil and gas production in North America has been linked to an increase in seismicity rate in these regions (Ellsworth, 2013). As fluid is pumped into deep formations, the state of stress within the subsurface changes, potentially reactivating pre-existing faults and/or causing subsidence or uplift of the surface. Therefore, hydraulic fracturing and/or fluid disposal injection can significantly increase the seismic hazard to communities and structures surrounding the injection sites (Barnhart et al., 2014). On 17th May 2012 an Mw4.8 earthquake occurred near Timpson, TX and has been linked with wastewater injection operations in …

Geophysical Study Of Complex Meteorite Impact Structures, William Zylberman

Electronic Thesis and Dissertation Repository

Hypervelocity impact craters are the most abundant morphologic features on rocky planetary bodies of the Solar System, except on Earth where they have mostly been erased by plate tectonics, erosion, or are buried under sediments. The internal structure of complex impact craters can only be studied on Earth by using ground-truth geophysical and geological studies. Such approaches - combined with modeling - can reveal how impact cratering, target geological composition, erosion and other post-impact processes can lead to the observed geophysical anomalies, which could also be detected by remote geophysical data on other planetary surfaces. In this work, a multidisciplinary …

New Gps Time Series Analysis And A Simplified Model To Compute An Accurate Seasonal Amplitude Of Tropospheric Delay, Hadis Samadi Alinia

Electronic Thesis and Dissertation Repository

Horizontal and vertical deformation of the Earth’s crust is due to a variety of different geophysical processes that take place on various spatiotemporal scales. The quality of the observations from spaced-based geodesy instruments such as Global Positioning System (GPS) and differential interferometric synthetic aperture radar (DInSAR) data for monitoring these deformations are dependent on numerous error sources. Therefore, accurately identifying and eliminating the dominant sources of the error, such as troposphere error in GPS signals, is fundamental to obtain high quality, sub-centimeter accuracy levels in positioning results.

In this work, I present the results of double-differenced processing of five years …

A Comparison Of Ground Motion Characteristics From Induced Seismic Events In Alberta With Those In Oklahoma, Krista M. Kaski

Electronic Thesis and Dissertation Repository

Ground motions from potentially-induced seismic events in Alberta of magnitude (M) > 3, recorded within 100 km, are empirically characterized in terms of their response spectral shapes and amplitudes. Ground motions are compared statistically to those from induced events in Oklahoma, as well as to three benchmark ground motion prediction equations (GMPEs), derived from natural events. Discrepancies between Alberta and Oklahoma events appear to be magnitude-dependent, and distance-independent. For events greater than M~4, the ground motions appear equivalent in the two regions. High-frequency motions from M< 3.5 events in Alberta are weaker than those of natural events, even those at shallow focal depths. For larger magnitudes, the residuals between the Alberta motions and benchmark GMPEs (Yenier and Atkinson, 2015; Atkinson, 2015; Abrahamson et al., 2014) suggest that observations are in reasonable accord with the models. These results provide a further understanding of ground motions from induced events in Alberta.

Assessment Of Earthquake Site Amplification And Application Of Passive Seismic Methods For Improved Site Classification In The Greater Vancouver Region, British Columbia, Frederick Andrew Jackson

Electronic Thesis and Dissertation Repository

There is renewed interest to improve seismic microzonation mapping in Greater Vancouver, British Columbia (BC). We investigate local geology as the cause of observed variable ground shaking from the 2015 M 4.7 Vancouver Island earthquake. We observe high amplification at 4-6 Hz on thick sediment and the northern edge of the Fraser River delta, and disparities with current regional seismic microzonation mapping. Site amplification and shear-wave velocity (V_S) are assessed from the first borehole earthquake recordings in BC. We also perform ambient vibration analyses at 13 new locations in southwest BC to highlight suitability of passive seismic methods …

Petrophysical Investigations Of The Marathon Cu-Pge Deposit, Marathon, On, Hiruni Gunawardana

Electronic Thesis and Dissertation Repository

Drill core samples obtained from four mineralized zones of the Marathon Cu-PGE deposit in the Coldwell igneous complex have been investigated for their petrophysical characteristics. Remanent magnetization was used as a possible tool to reorient core samples but a drilling induced overprint magnetization dominated the record. Anisotropy of magnetic susceptibility was measured to provide a proxy for the petrofabric of samples obtained from oriented drill cores; a well-defined planar fabric was found to strike 177 and dip 25°W, with down-dip lineation, in excellent agreement with inferred magmatic flow direction based on 3D modeling of mineralized footwall troughs. Magnetite rich lithologies …

The First Earthquake Site Assessments In Alberta, Canada, Joseph J. Farrugia

Electronic Thesis and Dissertation Repository

A thorough characterization of the site conditions at Alberta seismic stations is a vital component in assessing seismic hazard in the province. This thesis provides the first earthquake site characterizations in Alberta, including shear-wave velocity (V_S) depth profiles, estimates of the average shear-wave velocity in the upper 30 m (V_S30) and peak frequency (f_peak), and their validation for prediction of earthquake site amplification. National Building Code of Canada site classes are limited to C and D based on V_S30 estimates, with D being the predominant site class. Three …

Using Bolide Airwaves To Estimate Meteoroid Source Characteristics And Window Damage Potential, Nayeob Gi

Electronic Thesis and Dissertation Repository

We examined the far-field infrasonic signals produced by 78 bolides simultaneously detected by U.S. government sensors to determine the mechanisms responsible for interstation spreads in infrasound signal period. These signal period spreads lead to large variances in source energy estimates. Our analysis suggests that while acoustic source height contributes to some extent to the variance in signal periods, the range from the source to the station and in particular station noise plays a more significant role.

By simulating the near-field weak shocks from a suite of well-observed energetic fireballs, we have empirically estimated how often fireball shocks produce overpressure ( …

Developing And Testing A Model Of Site Amplification For Southern Ontario, Sebastian Braganza

Electronic Thesis and Dissertation Repository

Commonly-applied methods to estimate ground-motion amplification for earthquake hazard applications in southern Ontario are highly generalized. Site amplification effects have typically been estimated by a parameter that is not well-known in the region, the time-averaged shear-wave velocity in the top 30 metres of soil; V_S30. Moreover, V_S30 is not well correlated with site amplification in this region. This study develops a model that can better estimate ground motions and shaking intensities in southern Ontario based on readily-available information. The model is based on a site’s peak response frequency (f_peak), which can be estimated from depth-to-bedrock. …

Full-Waveform Inversion With Scaled-Sobolev Preconditioning Applied To Vibroseis Field Data, Benjamin Paul Consolvo

Electronic Thesis and Dissertation Repository

I present an application of a high-resolution subsurface imaging technique known as “full-waveform inversion” (FWI) to a vibroseis seismic dataset from eastern Ohio, USA. The data were collected over a crooked line with rough topography, 3.5 km maximum offsets, and no significant frequency content below 12 Hz. These parameters present challenges to obtaining quality images from FWI. The use of a preconditioner–the ‘scaled-Sobolev preconditioner’ (SSP - Zuberi and Pratt, 2017)–on the gradient of the misfit functional was key to obtaining low wavenumbers without discarding high wavenumbers. The results represent the first successful application of FWI with the SSP to a …