Thesis advisor: John E. Ebel / Drilling operations and extraction of oil and gas (O&G) may lead to subsurface slumping or compression of sediments due to reduced vertical principal stress which may lead to small earthquakes at the drilling site. O&G extraction is common in the northern Gulf of Mexico (NGM) and only thirty-five earthquakes of magnitudes between 2.3 and 6.0 have been recorded in the area from 1974 to the present. The purpose of this research is to detect more earthquakes using stacks of seismic data from the Transportable USArray (TA) from 2011 to 2013, and determine the spatiotemporal relationship between the detected earthquakes and O&G extraction. Five new small offshore earthquakes, that may be associated with the offshore O&G production, have been detected in the data. Spatial correlation of the epicenters with offshore drilling sites shows that the earthquakes may be due to the O&G extraction. / Thesis (MS) — Boston College, 2015. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

Rising incidents of earthquakes caused by human activity in the United States, known as induced earthquakes, is a growing concern. Induced earthquakes may occur when fluid and/or wastewater is injected several kilometers beneath the Earth’s surface into sedimentary rocks. Fluids and pressures can migrate from the sedimentary rocks, which are typically friendlier to fluid flow, into underlying less friendlier crystalline rocks along fluid pathways weakening and possibly reactivating preexisting faults. Understanding potential fluid pathways and/or barriers from the sedimentary rocks to crystalline rocks is crucial. I investigate the structure, composition, and heterogeneity of rocks near the contact between the sedimentary and crystalline rocks, known as nonconformities, and highlight their possible role in the transmission of fluids and porefluid pressures into the crystalline basement. To characterize nonconformities, we examined outcrop analogs and drillcore of nonconformities in New Mexico, Colorado, and Michigan. Geochemical, structural, and hydrological techniques were used to analyze the nonconformities at microscopic to megascopic scales. The nonconformities observed in this study consist of variably deformed, weathered, and altered igneous and metamorphic crystalline basement overlain by sedimentary rocks cut by outcrop- and map-scale faults. The nonconformity at the New Mexico sites includes a clay-rich weathered horizon atop deformed and jointed crystalline basement. Heterogeneity observed in the fracture and joint networks within the crystalline basement contributes to permeability heterogeneity and anisotropy. The crystalline basement adjacent to the nonconformity at the Colorado site is relatively fresh and unweathered and overlain by low permeability sandstones. The nonconformity and underlying slates in the Michigan drillcore are overprinted by hydrothermal alteration and carbonate mineralization, which provides evidence of hydrological communication between sedimentary and crystalline rocks. The nonconformities display a range of structural, hydrological, and geochemical styles and characteristics which vary over relatively small spatial extents. The geological and hydrogeological histories and complexities of nonconformity analogs provide valuable information to understand how fluids, past, and present, interact with the contact. This study introduces some of the factors that may control fluid flow adjacent to nonconformities and their possible significance to the interplay of deformation, fluid flow, and induced seismicity.

Pore pressure exists ubiquitously in the Earth’s subsurface and very often exhibits a cyclic loading on pre-existing faults due to seasonal and tidal changes, as well as the impoundment and discharge of surface reservoirs. The effect of oscillating pore pressure on induced seismicity is not fully understood. This effect exhibits a dynamic variation in effective stresses in space and time. The redistribution of pore pressure as a result of fluid flow and pressure oscillations can cause spatial and temporal changes in the shear strength of fault zones, which may result in delayed and protracted slips on pre-existing fractures. This research uses an experimental approach to investigate the effects of oscillating pore pressure on induced seismicity. With the aid of geophysical techniques, the spatial and temporal distribution of seismic events was reconstructed and analysed. Triaxial experiments were conducted on two types of sandstone, one with low permeability (Fontainebleau sandstone) and the other with high permeability (Darley Dale sandstone). Cyclic pore pressures were applied to the naturally-fractured samples to activate and reactivate the existing faults. The results indicate that the mechanical properties of the sample and the heterogeneity of the fault zone can influence the seismic response. Initial seismicity was induced by applying pore pressures that exceeded the previous maximum attained during the experiment. The reactivation of faults and foreshock sequences was found in the Fontainebleau sandstone experiment, a finding which indicates that oscillating pore pressure can induce seismicity for a longer period of time than a single-step increase in pore pressure. The corresponding strain change due to cyclic pore pressure changes suggests that progressive shearing occurred during the pore pressure cycles. This shearing progressively damaged the existing fault through the wearing of asperities, which in turn reduced the friction coefficient and, hence, reduced the shear strength of the fault. This ‘slow’ seismic mechanism contributed to the prolonged period of seismicity. This study also applied a material forecast model for the estimation of time-to-failure or peak seismicity in reservoir-induced seismicity, which may provide some general guidelines for short-term field case estimations.

Pore pressure exists ubiquitously in the Earth’s subsurface and very often exhibits a cyclic loading on pre-existing faults due to seasonal and tidal changes, as well as the impoundment and discharge of surface reservoirs. The effect of oscillating pore pressure on induced seismicity is not fully understood. This effect exhibits a dynamic variation in effective stresses in space and time. The redistribution of pore pressure as a result of fluid flow and pressure oscillations can cause spatial and temporal changes in the shear strength of fault zones, which may result in delayed and protracted slips on pre-existing fractures. This research uses an experimental approach to investigate the effects of oscillating pore pressure on induced seismicity. With the aid of geophysical techniques, the spatial and temporal distribution of seismic events was reconstructed and analysed. Triaxial experiments were conducted on two types of sandstone, one with low permeability (Fontainebleau sandstone) and the other with high permeability (Darley Dale sandstone). Cyclic pore pressures were applied to the naturally-fractured samples to activate and reactivate the existing faults. The results indicate that the mechanical properties of the sample and the heterogeneity of the fault zone can influence the seismic response. Initial seismicity was induced by applying pore pressures that exceeded the previous maximum attained during the experiment. The reactivation of faults and foreshock sequences was found in the Fontainebleau sandstone experiment, a finding which indicates that oscillating pore pressure can induce seismicity for a longer period of time than a single-step increase in pore pressure. The corresponding strain change due to cyclic pore pressure changes suggests that progressive shearing occurred during the pore pressure cycles. This shearing progressively damaged the existing fault through the wearing of asperities, which in turn reduced the friction coefficient and, hence, reduced the shear strength of the fault. This ‘slow’ seismic mechanism contributed to the prolonged period of seismicity. This study also applied a material forecast model for the estimation of time-to-failure or peak seismicity in reservoir-induced seismicity, which may provide some general guidelines for short-term field case estimations.

Thesis (M.S. in E.A.S.)--School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 2004. Directed by James Gaherty. / Includes bibliographical references (leaves 38-42).

Comprehensive and reliable seismic analysis techniques can aid in achieving successful inference of rockmass behaviour in different stages of the caving process. This case study is based on field data from Telfer sublevel caving mine in Western Australia. A seismic monitoring database was collected during cave progression and breaking into an open pit 550 m above the first caving lift. Five seismic analyses were used for interpreting the seismic events. Interpretation of the seismic data identifies the main effects of the geological features on the rockmass behaviour and the cave evolution. Three spatial zones and four important time periods are defined through seismic data analysis. This thesis also investigates correlations between the seismic event rate, the rate of the seismogenic zone migration, mucking rate, Apparent Stress History, Cumulative Apparent Volume rate and cave behaviour, in order to determine failure mechanisms that control cave evolution at Telfer Gold mine.

Automated location of seismic events is a very important task in microseismic monitoring operations as well for local and regional seismic monitoring. Since microseismic records are generally characterised by low signal-to-noise ratio, such methods are requested to be noise robust and sufficiently accurate. Most of the standard automated location routines are based on the automated picking, identification and association of the first arrivals of P and S waves and on the minimization of the residuals between theoretical and observed arrival times of the considered seismic phases. Although current methods can accurately pick P onsets, the automatic picking of the S onset is still problematic, especially when the P coda overlaps the S wave onset. In this thesis I developed a picking free automated method based on the Short-Term-Average/Long-Term-Average (STA/LTA) traces at different stations as observed data. I used the STA/LTA of several characteristic functions in order to increase the sensitiveness to the P wave and the S waves. For the P phases we use the STA/LTA traces of the vertical energy function, while for the S phases, we use the STA/LTA traces of the horizontal energy trace and then a more optimized characteristic function which is obtained using the principal component analysis technique. The orientation of the horizontal components can be retrieved by robust and linear approach of waveform comparison between stations within a network using seismic sources outside the network (chapter 2). To locate the seismic event, we scan the space of possible hypocentral locations and origin times, and stack the STA/LTA traces along the theoretical arrival time surface for both P and S phases. Iterating this procedure on a three-dimensional grid we retrieve a multidimensional matrix whose absolute maximum corresponds to the spatial and temporal coordinates of the seismic event. Location uncertainties are then estimated by perturbing the STA/LTA parameters (i.e the length of both long and short time windows) and relocating each event several times. In order to test the location method I firstly applied it to a set of 200 synthetic events. Then we applied it to two different real datasets. A first one related to mining induced microseismicity in a coal mine in the northern Germany (chapter 3). In this case we successfully located 391 microseismic event with magnitude range between 0.5 and 2.0 Ml. To further validate the location method I compared the retrieved locations with those obtained by manual picking procedure. The second dataset consist in a pilot application performed in the Campania-Lucania region (southern Italy) using a 33 stations seismic network (Irpinia Seismic Network) with an aperture of about 150 km (chapter 4). We located 196 crustal earthquakes (depth < 20 km) with magnitude range 1.1 < Ml < 2.7. A subset of these locations were compared with accurate locations retrieved by a manual location procedure based on the use of a double difference technique. In both cases results indicate good agreement with manual locations. Moreover, the waveform stacking location method results noise robust and performs better than classical location methods based on the automatic picking of the P and S waves first arrivals. / Die automatische Lokalisierung seismischer Ereignisse ist eine wichtige Aufgabe, sowohl im Bereich des Mikroseismischen Monitorings im Bergbau und von Untegrund Aktivitäten,  wie auch für die lokale und regionale Überwachung von natürlichen Erdbeben. Da mikroseismische Datensätze häufig ein schlechtes Signal-Rausch-Verhältnis haben müssen die Lokalisierungsmethoden robust gegen Rauschsignale und trotzdem hinreichend genau sein. Aufgrund der in der Regel sehr hochfrequent aufgezeichneten Messreihen und der dadurch sehr umfangreichen Datensätze sind automatische Auswertungen erstrebenswert. Solche Methoden benutzen in der Regel automatisch gepickte und  den P und S Phasen zugeordnete Ersteinsätze und Minimieren die Summe der quadratischen Zeitdifferenz zwischen den beobachteten und theoretischen Einsatzzeiten. Obgleich das automatische Picken der P Phase in der Regel sehr genau möglich ist, hat man beim Picken der S Phasen häufig Probleme, z.B. wenn die Coda der P Phase sehr lang ist und in den Bereich der S Phase hineinreicht. In dieser Doktorarbeit wird eine Methode vollautomatische, Wellenform-basierte Lokalisierungsmethode entwickelt, die Funktionen des Verhältnisses "Short Term Average / Long Term Average"  (STA/LTA) verwendet und keine Pickzeiten invertiert. Die STA/LTA charakteristische Funktion wurde für unterschiedliche Wellenform Attribute getestet, um die Empfindlichkeit für P und S Phasen zu erhöhen. Für die P Phase wird die STA/LTA Funktion für die Energie der Vertikalkomponente der Bodenbewegung benutzt, wohingegen für die S Phase entweder die Energie der horizontalen Partikelbewegung oder eine optimierte Funktion auf Basis der Eigenwertzerlegung benutzt wird. Um die Ereignisse zu lokalisieren wird eine Gittersuche über alle möglichen Untergrundlokalisierungen durchgeführt. Für jeden räumlichen und zeitlichen Gitterpunkt werden die charakteristischen Funktionen entlang der theoretischen Einsatzkurve aufsummiert. Als Ergebnis erhält man eine 4-dimensionale Matrix über Ort und Zeit des Ereignisses, deren Maxima die wahrscheinlichsten Lokalisierungen darstellen. Um die Unsicherheiten der Lokalisierung abzuschätzen wurden die Parameter der STA/LTA Funktionen willkürlich verändert und das Ereignis relokalisiert. Die Punktwolke aller möglichen Lokalisierungen gibt ein Maß für die Unsicherheit des Ergebnisses. Die neu entwickelte Methode wurde an einem synthetischen Datensatz von 200 Ereignissen getestet und für zwei beobachtete Datensätze demonstriert. Der erste davon betrifft induzierte Seismizität in einem Kohlebergbau in Norddeutschland. Es wurden 391 Mikrobeben mit Magnituden zwischen Ml 0.5 und 2.0 erfolgreich lokalisiert und durch Vergleich mit manuell ausgewerteten Lokalisierungen verifziert.Der zweite Datensatz stammt von einem Anwednung auf des Regionale Überwachungsnetz in der Region Campania-Lucania (Süditalien)  mit 33 seismischen Stationen und einer Apertur von etwa 150 km. Wir konnten 196 Erdbeben mit Tiefen < 20 km und Magnituden zwischen Ml 1.1 und 2.7 lokalisieren. Eine Untergruppe der eigenen Lokalisierungen wurde mit den Lokalisierungen einer Standard Lokalisierung sowie einer  hochgenauen Relativlokalisierung verglichen. In beiden Fällen ist die Übereinstimmung mit den manuellen Lokalisierungen groß. Außerdem finden wir, dass die Wellenform Summations Lokalisierung ronbust gegen Rauschen ist und bessere Ergebnisse liefert als die Standard Lokalisierung, die auf dem automatischen Picken von Ersteinsatzzeiten alleine basiert.

Η περιοχή του κόλπου του San Francisco είναι μια πολύ σεισμογενής περιοχή.Η σεισμικότητα οφείλεται στις τεκτονικές πλάκες (πλάκα του Ειρηνικού Ωκεανού και η πλάκα της Βόρειας Αμερικής) που κινούνται η μία σε σχέση με την άλλη. Τα όρια αυτών των πλακών ή η αλληλεπίδρασή τους εκφράζεται από τα ρήγματα της περιοχής, όπως το ρήγμα του Αγίου Ανδρέα και το ρήγμα του Hayward, τα οποία είναι ενεργά.Η ενεργός τεκτονική της περιοχής έχει σαν απότέλεσμα την εντυπωσιακή μορφολογία της περιοχής του κόλπου του San Francisco. Σειρά ισχυρών σεισμών έχουν πλήξει την περιοχή με βάση στοιχεία παλαιοσεισμολογίας κατά τους ιστορικούς χρόνους. Με βάση τα δεδομένα αυτά και την αρχή του ομοιομορφισμού εκτιμάται ότι παρόμοιου μεγέθους σεισμοί θα πλήξουν την περιοχή και στο άμεσο μέλλον. Οι προβλέψεις των επιστημόνων συγκλίνουν στο συμπέρασμα ότι στα επόμενα χρόνια, οι άνθρωποι θα ξαναδοκιμαστούν από τη σεισμική δράση στην περιοχή του San Francisco. Η ερευνητική δραστηριότητα των επιστημόνων στοχεύει στο να μετριασθούν οι επιπτώσεις αυτές οι οποίες είναι πολυποίκιλες και απαριθμούνται στη συνέχεια. Οι καταστροφές από τους σεισμούς διαχωρίζονται σε πρωτογενείς και δευτερογενείς. Στις δευτερογενείς που είναι και οι πιο καταστροφικές για το δομημένο περιβάλλον συγκαταλέγονται οι αστοχίες του δικτύου ύδρευσης, οι καταρρεύσεις ή οι βλάβες των σπιτιών και η υποβάθμιση στην ποιότητα των αποθεμάτων του πόσιμου νερού της μητροπολιτικής περιοχής. Επίσης οι σεισμοί προκαλούν τσουνάμι, ρευστοποιήσεις εδάφους, πυρκαγιές, θανάτους ανθρώπων, αλλά και υλικές ζημιές σε όλες τις κατασκευές του ανθρώπου. / The region of the Gulf of San Francisco is a very activity region. Seismicity is owed in the tectonic plates (plate of Pacific Ocean and the plate of Northern America) that they are moved the one concerning the other. The limits of these plates or the interaction to them it is expressed by the faults of region, as the fault of San Andreas and the fault of Hayward, which are active. The active tectonics of region have as result the impressive morphology of San Francisco bay region. Many earthquakes have affected the region. scientists appreciate that similar size earthquakes will also affect the region in the direct future. The inquiring activity of scientists aims in are moderated this repercussions. Τhe destructions by the earthquakes are separated in primary and secondary. In secondary that are also most devastating are included damages of water supply, collapse or the damage of houses and the devalorisation in the quality of reserves of potable water of metropolitan region. Also the earthquakes cause tsoynamis, liquidations of ground, fires, deaths of persons but also material damage in all the human manufactures.

abstract: The goal of this study is to gain a better understanding of earthquake distribution and regional tectonic structure across Arizona. To achieve this objective, I utilized seismic data from EarthScope's USArray Transportable Array (TA), which was deployed in Arizona from April 2006 to March 2009. With station spacing of approximately 70 km and ~3 years of continuous three-component broadband seismic data, the TA provided an unprecedented opportunity to develop the first seismicity catalog for Arizona without spatial sampling bias. In this study I developed a new data analysis workflow to detect smaller scale seismicity across a regional study area, which serves as a template for future regional analyses of TA data and similar datasets. The final event catalog produced for this study increased the total number of earthquakes documented in Arizona by more than 50% compared to the historical catalog, despite being generated from less than three years of continuous waveform data. I combined this new TA catalog with existing earthquake catalogs to construct a comprehensive historical earthquake catalog for Arizona. These results enabled the identification of several previously unidentified areas of seismic activity within the state, as well as two regions characterized by seismicity in the deeper (>20 km) crust. The catalog also includes 16 event clusters, 10 of which exhibited clear temporal clustering and swarm-like behavior. These swarms were distributed throughout all three physiographic provinces, suggesting that earthquake swarms occur regardless of tectonic or physiographic setting. I also conducted a case study for an earthquake swarm in June of 2007 near Theodore Roosevelt Lake, approximately 80 miles northeast of Phoenix. Families of events showed very similar character, suggesting a nearly identical source location and focal mechanism. We obtained focal mechanisms for the largest of these events, and found that they are consistent with normal faulting, expected in this area of the Arizona Transition Zone. Further, I observed no notable correlation between reservoir water level and seismicity. The occurrence of multiple historical earthquakes in the areas surrounding the reservoir indicates that this swarm was likely the result of tectonic strain release, and not reservoir induced seismicity. / Dissertation/Thesis / Appendix A: Earthquakes recorded by EarthScope USArray / Appendix B: Total Arizona earthquake catalog / Appendix B: Earthquake catalog references / Appendix D: Mine Blast data / Appendix D: Potential mine blasts / Appendix D: Arizona blasting sites / Appendix E: Earthquake clusters / Appendix F: Antelope tutorial and parameter files / Appendix C: Stations used in this study / M.S. Geological Sciences 2011

The midcontinent United States, a region which typically does not experience many earthquakes, has experienced a significant increase in the number of earthquakes over the last decade. This increase in earthquake activity has been linked to wastewater injection, a process in which large volumes of wastewater from oil and gas extraction are injected into deep (2-3 km), high-permeability sedimentary rocks, near low-permeability Precambrian (>540-million-year-old) crystalline ‘basement’ rocks. The contact between these two rock types is referred to as the Precambrian nonconformity. Injection-induced earthquakes occur on or near basement-hosted faults due to an increase in pore fluid pressures, which implies that there may be a hydrological connection between the basement-hosted faults and the injection point. We hypothesize that the Precambrian nonconformity greatly influences this hydrological connection. We investigate the geologic properties of Precambrian nonconformity zone outcrop and core analogs to examine how the geology of the nonconformity zone controls fluid flow. Methods include mapping of geological materials and deformation structures (faults and fractures), mineralogical analysis, and geochemical analysis. These data sets allow us to infer the nature of fluid flow in the past, and make predictions about fluid flow in the future. In addition, this information is used to inform hydrological models, improving the ability to predict earthquakes due to wastewater injection. We identify three main geological scenarios that are likely to be encountered at the nonconformity. These are: 1) basal conglomerate, 2) weathered/altered horizon, and 3) mineralized contacts. These scenarios, or combinations of these scenarios, may be fractured or faulted, resulting in a variety of hydrological implications. The permeability of basal conglomerates and weathered horizons at the contact depends on the textures and minerals that are present. Regolith, clast-supported granitic wash, or poorly cemented conglomeratic horizons, may act as high permeability conduits, whereas a clay-rich grus or granitic wash, or tightly cemented conglomerate, may act as low permeability barriers. Mineralized contacts may act as low permeability barriers due to a reduction of pore space. The mineralized contact shows that the introduction of warm brines by modern injection may result in mineralization or chemical weathering, dynamically affecting permeability over time depending on the mineralogy of the host rock and chemical composition of the injected brine.