The presence of active fault traces in proximity to any new infrastructure project is a major concern for the design process. The relative displacements that can be experienced in surface fault rupture during a seismic event must be either entirely avoided or mitigated in some way. Blind faults present a significant challenge to engineers attempting to identify these hazards. Current standards of practice employed to locate these features are time consuming and costly. This work investigates the geophysical methods of refraction microtremor (ReMi) and seismic refraction with regard to their applicability in this task. By imaging a distinct lateral variation in the shear wave velocity (Vs) profile across a short horizontal distance, these methods may provide a means of constraining traditional investigation techniques to a more focused area. The ReMi method is still very new, but holds key advantages over other geophysical methods in its ease of application and ability to achieve good results in highly urban settings. It is one of the few geophysical techniques that does not suffer in the presence of high amplitude ambient vibrations. The seismic refraction method is here applied in an attempt to corroborate data obtained through the ReMi analysis procedure. Sensitivity, precision parametric studies are carried out in order to learn how to best apply the ReMi method. Both tests are then applied at a previously trenched fault trace to determine whether the data can be matched to the subsurface information. Finally, the methods are deployed at a location with an inferred fault trace where little to nothing is known about the subsurface. The precision study indicates a coefficient of variation for the ReMi method on the order of 7%. At the known fault trace both methods generally agree qualitatively with available subsurface data and each other. Using the ReMi method, a marked shift is observed in the Vs profile laterally across the fault trace. In the case of the inferred fault trace, the same type of lateral variation in the V­­s profile is observed using the ReMi method. The seismic refraction at this site does not agree with the ReMi data, but seems reasonable given the visible geomorphology. Receiver arrays placed in close proximity to the inferred fault trace recorded erratic signals during seismic refraction testing, and displayed abnormal response modes after transforming the ReMi data to frequency-slowness space. These anomalies may possibly be attributed to the presence of abnormal subsurface structural geometry indicative of faulting.

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A new interpretive slow-varying (long-wavelength) static estimation method is introduced to remove the effects of static anomalies caused by lateral variations in near-surface velocity. The application becomes critical where the wavelength of the variation of statics is larger than the maximum offset between source and receiver (spreadlength) used during data acquisition. The method used in this study utilizes the reflection and refraction arrival times from the shallowest reflector or refractor to determine the statics variations. The study include reprocessing of 12 seismic reflection data sets from the Savannah River Site area, near Aiken, South Carolina. The same data sets were also used to extract the refracted arrivals by the refraction stack processing. Application of the estimated slow-varying statics enhanced the S/N ratio, lateral continuity, and coherency for deep as well as shallow data and allowed to better determine the geometry of faults in the Coastal Plain sediments, which penetrate from the basement. Interpretation of the enhanced seismic reflection and generated seismic refraction sections helped to constrain the depth of upward penetration of the faults imaged in the seismic data. Refraction stack sections were used to obtain better definition of the delineation of the upward penetration of the faults at shallower depths. Despite the smoothing effect that is incorporated in the refraction stacks due to long refracted paths they exhibit clear-cut termination and offset on some of the lines in spatial zones where the Pen Branch fault can be projected in the shallow sediments. The seismic data indicate that the Coastal Plain sediments dip and thicken toward the southeast in the area. The basement top provides a high acoustic impedence contrast, and has a regional dip towards the southeast. The Pen Branch fault is one of the longest faults in the area, that acts as a basin bounding fault separating the Paleozoic crystalline basement from the Triassic basin fill. Other faults such as the Steel Creek and A TT A have also been discerned by the seismic data in the area. Small antithetic faults appear to join the Pen Branch and the A TT A fault. The offset of the Pen Branch fault (15 ms; 32 m) is relatively higher then the offsets observed for the ATTA (11.5 ms; 24.5 m) and Steel Creek (13 ms; 27.5 m) faults. The delineation of the upward depth of penetration of the Pen Branch fault is imaged best on lines 28 and 2EXP where the reflections at 0.18 to 0.2 s exhibit termination with amplitude changes, thereby suggesting the presence of the fault at that level. The offset associated with the A TT A fault can be traced up to 0.16 son line 27. The expression associated with the Steel Creek fault does not seem to go above 0.2 s. On the basis of the result from the interpretation of line 27, the upward depth of penetration of the A TT A fault in the Coastal Plain sediments reaches to a higher level then that of the Pen Branch fault. On the basis of the reflection and refraction data it is interpreted that the reactivation of the Pen Branch and the A TT A fault is as young as the age of the shallow reflector at 200 ms (top of Cretaceous?). / Master of Science

It is often claimed that the first Fresnel zone associated with the dominant frequency represents the spatial resolution limit of traveltime tomography. We show, however, that the relevant Fresnel limit for tomographic resolution is the maximum, not the dominant frequency in the data. For physically realizable causal wavelets, the maximum frequency is infinite. In practice, noise lowers the effective possible maximum frequency. To demonstrate these points, synthetic seismic data were generated for traveltime picking and inversion for a single, small velocity anomaly embedded in a homogeneous background velocity. A variety of traveltime picking techniques were tested and compared for their ability to detect the presence of objects smaller than that Fresnel zone associated with the dominant frequency. All methods produced accurate ray-theoretical (infinite-frequency) picks from noise-free seismic data for objects smaller than the dominant-frequency Fresnel zone. For the lowest dominant frequencies with Fresnel zones many times larger than the object, picking methods that focus on features along the onset of the first arrival were the most accurate, while cross-correlation with a known wavelet preformed less accurately. First-onset picking methods perform better because they take advantage of the highest frequencies in the data, whereas the correlation wavelet is typically in line with the dominant frequency. All methods successfully detected the presence of objects smaller than a wavelength. The inversion of the traveltime picks from the different picking methods always recovered the position and shape of the object. Random noise at a range of signal-to-noise ratios was then added to the seismic data and the data were repicked. Pick times with different noise realizations are statistically centered on the noise-free pick, not the time that would be recorded in the absence of the object. Trace stacking prior to picking or the averaging of many picks improves the signal-to-noise ratio and can extract signal that is not detected on an individual pick. An averaging of traveltime picks also occurs during tomographic inversion. This inherent signal-to-noise improvement allows tomography to image objects that are undetectable in individual trace picks. The resolution of tomography is limited not by the Fresnel zone associated with the dominant frequency, but by the accuracy of the traveltime picks. Resolution is further improved by dense ray coverage. / Master of Science

O presente trabalho de mestrado está inserido nos estudos de refração profunda do Projeto Temático 'Estudos Geofísicos e Modelo Tectônico dos Setores Central e Sudeste da Província Tocantins, Brasil Central'. Nesses estudos foram levantadas três linhas de refração de aproximadamente 300 km de extensão, duas no setor Central da Província Tocantins e uma no setor Sudeste, que é o objeto de estudo deste trabalho. Foram utilizados 111 sismógrafos digitais SGR pertencentes ao programa PASSCAL, instrumentos auxiliares do USGS, e 13 sismógrafos digitais e instrumentos auxiliares do IAG/USP. A linha sísmica teve aproximadamente 300 km de extensão com pontos de registro separados a cada 2,5 km, distribuídos ao longo de estradas principais e secundárias. A cada 50 km, aproximadamente, foi realizada uma explosão, nas explosões dos extremos da linha foram utilizados 1000 kg de explosivo e para a explosão central uma carga de 500 kg. Para a determinação das coordenadas geográficas dos pontos de tiro e de registro, foi utilizado o método diferencial com medidas de GPS. O principal objetivo deste trabalho foi obter como produto final um modelo de velocidades sísmicas contendo as características físicas das principais descontinuidades na crosta terrestre e no manto superior. Para análise e processamento dos dados foram utilizados os pacotes SAC, SU, SEIS. Para a modelagem foram utilizados a teoria do raio e a elaboração de sismogramas sintéticos, do pacote SEIS. Para a elaboração do modelo final foram utilizados os dados das explosões dos pontos extremos e central, tendo em vista que devido a problemas técnicos não foram registrados os sinais das outras 4 explosões. Além disso, as explosões registradas não apresentaram sinais claros em toda a extensão da linha. Devido a tudo isso e considerando as unidades geológicas presentes na região de estudo são sugeridos três modelos de velocidades sísmicas. O primeiro modelo refere-se ao tiro direto (EX31) localizado no extremo sudoeste da linha, sobre a Bacia do Paraná. Para este modelo obteve-se para superfície (0 km) a velocidade inicial de 2 km/s (coberturas); para a profundidade de 0,086 km a velocidade inicial é de 5,15 km/s (basalto); para a profundidade de 0,350 km obteve-se a velocidade inicial de 4,6 km/s (arenito - camada de baixa velocidade); para profundidade de 0,650 km a velocidade inicial é de 5,75 km/s e para profundidade de 4 km obteve-se a velocidade inicial de 6,07 km/s. O segundo modelo refere-se ao tiro reverso (EX34) localizado no centro da linha sobre granitóides do Grupo Araxá. Para este modelo obteve -se para superfície (0 km) a velocidade inicial de 2 km/s; para a profundidade de 0,06 km a velocidade inicial é de 5,69 km/s e para a profundidade de 0,860 km obteve-se a velocidade inicial de 6,25 km/s. Finalmente, o terceiro modelo refere-se ao tiro direto para toda a extensão da linha (300 km). Este modelo foi definido a partir de fases secundárias lidas nos registros e modelos anteriores propostos na literatura. Da superfície até os 4 km iniciais de profundidade este modelo é igual ao primeiro, para uma profundidade de 20 km obteve-se a velocidade inicial de 6,70 km/s e para uma profundidade de 40 km a velocidade é de 8,00 km/s (descontinuidade de MOHO). / This work to fulfil the degree of Master of Sciences is inserted among the deep seismic refraction studies of the Thematic Project 'Geophysical Studies and Tectonic Model of the Tocantins Province Central and Southeast Sectors, Central Brazil'. Three refraction lines, of around 300 km long each, were deployed, two of them in the Central sector and the other in the SE sector, that is subject of the present work. The equipment used in this experiment was composed by 111 SGR digital seismographs belonging to the PASSCAL Program. Complemented with auxiliary instruments from USGS and 13 seismographs belonging to IAG/USP. The space among the recording points was 2.5 km, which were located along main and secondary roads. Every 50 km was fired an explosion with 1000 kg of emulsion in each extreme and 500 kg in the central point. The geographical co-ordinates were determined by using the GPS differential method. The main objective of this work is to obtain as a final product a seismic velocity model with the physical characteristics of the main discontinuities in the crust and upper mantle. The packages SAC, SU and SEIS were used to perform the data analysis and processing. To carry on the modelling were used the ray theory and the synthetic seismograms construction, belonging to the SEIS package Data from the extreme and middle points of the seismic line were used to elaborate the final model, considering that due to technical problems signals from the other four explosions were not recorded. Apart from that, the recorded explosions did not present clear signals all along the extension of the line. Due to these facts, and considering also the geological units present in the studied region, are suggested three seismic velocity models. The first model is referred to the direct shot (EX31), which is localised in the Southwest extreme of the line on the Parana Basin province. In this model we obtained the P wave velocity (VP) of 2 km/sec at the surface, corresponding to the unconsolidated sediments and soil on the top of that basin. At a depth of 86 m we found VP of 5,15 km/sec and at a depth of 350 m the velocity VP of 4,6 km/sec, corresponding to the basalt and sand layers of the Parana Basin. Underlying them, at 650 m of depth we found the basement with VP of 5,75 km/sec and finally at a depth of 4 km there is a layer with VP of 6,07 km/sec, corresponding to a typical upper crust P wave velocity. The second model corresponds to the reverse shot (EX34) that is localised in the middle point of the line on the granitoides of the Araxa Group. For this model we obtained VP of 2 km/sec for the superficial layers, then at a depth of 60 m was obtained V P of 5,69 km/sec and for a depth of 860 m the value of V P is 6,25 km/sec. Finally, the third model belongs to the whole line section (300 km) from the direct shot (EX31). This model was obtained by using the arrivals of secondary phases and the results of models proposed in other works. From the surface down to 4 km of depth this model is similar to the first one. At 20 km of depth there is a layer with VP of 6,70 km/sec, corresponding to the lower crust, with Moho at a depth of 40 km with VP of 8,00 km/sec.

The Tualatin Valley is a well defined elliptical basin centered at Hillsboro, with a major axis trending roughly N65°W. The valley is bordered on the northeast by the Tualatin Mountains (Portland Hills) which are a faulted, northwest-trending asymmetrical anticline. Topographic and geophysical evidence have defined the Portland Hills fault, which occurs along the northeast side of the Tualatin Mountains. The possibility that a fault or fault zone occurs along the southwest side of the Tualatin Mountains was investigated in this study.

SP, resistivity/IP and seismic refraction responses of the Woodlawn Orebody and Mt.Bulga Deposit are examined and compared. Both exhibit similar responses produced mainly by uneconomic and disseminated sulphide mineralization and host rock features, demonstrating that the magnitude and character of electrical and seismic responses are not reliable indicators of size and economic sulphide content of volcanogenic sulphide ores. SP, soil geochemistry and electrogeochemistry are found to be the most effective exploration methods followed by resistivity/IP and seismic refraction. The large SP responses over both ore zones are simulated using new methods which allowed the width and depth of oxidation to be computed. Conventional and compensation array resistivity responses best define the deposits. Computer simulation shows that dipole- dipole and Unipole arrays are most useful. First order IP responses are large and similar, but the ore zones are not easily distinguished from polarizable host rocks. Second order responses, at Woodlawn, better define these lithologies and cross-plots of EM coupling removed first order parameters prove useful. The supergene and gossan zones are defined as sources of electrical anomalies and correlate with interpreted SP sources. Seismic velocities of fresh Woodlawn ore samples indicate only small contrasts with host rocks. Refraction travel-time data are highly complex but host rocks are clearly distinguished by their seismic velocities. Both deposits appear as low velocity zones at the general bedrock level which are shallower and narrower than the electrical sources associated with the ore zones. Extensive model simulation shows that the Reciprocal interpretation method is most useful when compared to other time- term methods for refraction interpretation but has some limitations. Computer simulation shows the significance of non- critical refractions, diffractions and laterally hidden zones which define the lateral resolution of the refraction method. The results of this study and the interpretative techniques developed will assist the exploration for similar and deeper massive volcanogenic orebodies in comparable geological environments.

Graduation date: 1988

Tez (Yüksek Lisans) - Süleyman Demirel Üniversitesi, Fen Bilimleri Enstitüsü, Jeofizik Mühendisliği Anabilim Dalı, 2008. / Kaynakça var.

The main cause of failure in embankment dams - which represent 75% of all dams in the world (ICOLD, 2018) - is the internal erosion produced by excessive seepage not accounted for in their designs. This erosion can cause that a small anomalous structure, not likely to be considered as risky, turns rapidly into a significant structural damage if not recognized on time. This creates a necessity for methods that can detect these anomalies in a non-intrusive, cost-effective and sensitive way. The purpose of this work is to analyse the strength of three geophysical methods (ERT and Seismic Refraction and Reflection) in detecting and accurately localizing anomalous structures inside an embankment dam. This study has been successfully approached in two different ways: by synthetic modelling and by an experimental field work at an embankment dam in northern Sweden. The results show that these methods are capable of detecting different structures in the interior of the dam in an accurate and rapid manner. / Den främsta orsaken till brister i jordfyllningsdammar, som utgör 75% av alla dammar i världen (ICOLD, 2018) och är föremål för detta arbete, är inre erosion som orsakas av extrem läckage som togs inte med i beräkningar i deras konstruktioner. Denna erosion kan resultera i att en liten anomal struktur, som sannolikt inte anses vara riskabel, snabbt blir en betydande strukturell skada om den inte är uppmärksammas i tid. Därför krävs metoder som kan upptäcka dessa anomalier på ett icke-påträngande, kostnadseffektivt och känsligt sätt. Syftet med detta arbete är att analysera möjligheterna med tre geofysiska metoder (ERT, Seismisk Refraktion och Seismisk Reflektion) för att upptäcka och exakt lokalisera anomala strukturer inuti en jordfyllningsdamm. Denna studie har utförts på två fronter: genom (i) syntetisk modellering och (ii) ett experimentellt fältarbete vid en damm i norra Sverige. Resultaten visar att dessa metoder kan detektera olika strukturer inuti dammen på ett pålitligt och snabbt sätt.