Дисертації з теми "Crustal tomography"
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Liu, Kui. "Surface Wave Propagation and Global Crustal Tomography." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/25428.
Повний текст джерелаPh. D.
Lynner, Colton, and Robert W. Porritt. "Crustal structure across the eastern North American margin from ambient noise tomography." AMER GEOPHYSICAL UNION, 2017. http://hdl.handle.net/10150/625356.
Повний текст джерелаVillagomez, Diaz Darwin R. 1973. "Crustal and upper mantle structure beneath the Galapagos arechipelago from seismic tomography." Thesis, University of Oregon, 2010. http://hdl.handle.net/1794/11071.
Повний текст джерелаTo explain the origin of several distinct aspects of the Galápagos volcanic hotspot, such as the broad geographical extent of recent volcanism and the unusual pattern of geochemical anomalies, we conducted seismic tomography studies of the upper mantle and crust beneath the Galápagos Archipelago. The studies combine measurements of group and phase velocities of surface waves and delay times of body waves. We find that upper mantle seismic velocities are lower than those beneath other regions of comparable age in the Pacific and consistent with an excess temperature of 30 to 150°C and ∼0.5% melt. We attribute the excess temperature and presence of melt to an upwelling thermal mantle plume. Crustal seismic velocity is up to 25% lower than that of very young crust at the East Pacific Rise (EPR) and is comparable to that of Hawaii, which we attribute to heating by increased intrusive activity above the Galápagos plume and the construction of a highly porous volcanic platform. In addition, we find that the Galápagos hotspot is underlain by a high-velocity region whose thickness varies from 40 to 100 km. The tomographic images reveal that the upwelling mantle plume tilts northward (towards the nearby Galápagos Spreading Center) as it rises and then spreads laterally when it reaches the bottom the lid. The lid, which we attribute to residuum from melting, is thickest where it is farthest from the spreading center, suggesting that ridge processes may affect the generation and amount of thinning of the residuum layer. In addition, the thickness of the lid correlates well with the geographical pattern of geochemical anomalies of erupted lavas, suggesting that the lid may control the final depth of decompression melting. We conclude that many of the distinct characteristics of the Galápagos can be attributed to the interaction of the upwelling plume with the lid and the nearby ridge. We further suggest that the ridge affects the geometry of plume upwelling in the upper mantle and also the pattern of lateral spreading of the plume due to its effect on the thickness of the residuum layer. This dissertation includes previously published co-authored material.
Committee in charge: Dr. Douglas R. Toomey, Chairperson; Dr. Eugene Humphreys, Member; Dr. Emilie Hooft Toomey, Member; Dr. Paul Wallace, Member; Dr. John Conery, Outside Member
Day, Anthony James. "Seismic imaging of crustal structure at mid-ocean ridges : a three-dimensional approach." Thesis, Durham University, 2001. http://etheses.dur.ac.uk/4274/.
Повний текст джерелаBeachly, Matthew William 1986. "The Upper Crustal P-wave Velocity Structure of Newberry Volcano, Central Oregon." Thesis, University of Oregon, 2011. http://hdl.handle.net/1794/11475.
Повний текст джерелаThe upper-crustal seismic-velocity structure of Newberry volcano, central Oregon, is imaged using P-wave travel time tomography. The inversion combines a densely-spaced seismic line collected in 2008 with two USGS seismic experiments from the 1980s. A high-velocity ring (7 km EW by 5 km NS) beneath the inner caldera faults suggests an intrusive ring complex 200 to 500 m thick. Within this ring shallow low velocities (<2 km depth) are interpreted as caldera fill and a subsided block. High velocities below 2 km depth could be intrusive complexes. There appears to be a low-velocity body at 3-6 km depth beneath the center of the volcano. This region is poorly resolved in the inversion because the ray paths bend around the low-velocity body. The 2008 data also recorded a secondary arrival that may be a delayed P-wave interacting with the low-velocity body.
Committee in charge: Emilie E.E. Hooft, Chairperson; Douglas R. Toomey, Member; Katharine V. Cashman, Member
White, Donald John. "Shallow crustal structure beneath the Juan de Fuca ridge from 2[sup D] seismic refraction tomography." Thesis, University of British Columbia, 1989. http://hdl.handle.net/2429/29317.
Повний текст джерелаScience, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate
Van, Avendonk Hermanus Josephus Antonius. "An investigation of the crustal structure of the Clipperton transform fault area using 3D seismic tomography /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1998. http://wwwlib.umi.com/cr/ucsd/fullcit?p9823314.
Повний текст джерелаDelph, Jonathan, and Jonathan Delph. "Crustal and Upper Mantle Structure of the Anatolian Plate: Imaging the Effects of Subduction Termination and Continental Collision with Seismic Techniques." Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/622908.
Повний текст джерелаKashubin, Artem. "Seismic Studies of Paleozoic Orogens in SW Iberia and the Middle Urals." Doctoral thesis, Uppsala universitet, Geofysik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9405.
Повний текст джерелаHardwick, Anthony James. "New insights into the crustal structure of the England, Wales and Irish Seas areas from local earthquake tomography and associated seismological studies." Thesis, University of Leicester, 2009. http://hdl.handle.net/2381/8615.
Повний текст джерелаTiberi, Lara. "Tomografia crostale della Pianura Padana e calibrazione di procedure di localizzazione." Doctoral thesis, Università degli studi di Trieste, 2014. http://hdl.handle.net/10077/10125.
Повний текст джерелаI terremoti costituiscono un disastro naturale ricorrente su tutto il territorio italiano e per questo sono estremamente importanti interventi mirati e rapidi di protezione civile. La rapidità di questi interventi dipende dalla produzione di localizzazioni veloci e possibilmente in tempo reale degli eventi sismici. La precisione delle localizzazioni, inoltre, è necessaria per identificare le faglie sismogenetiche. Per questi due aspetti, è necessario un miglioramento dei sistemi di monitoraggio esistenti in modo da poter accrescere la qualità delle localizzazioni automatiche in tempo reale. Lo scopo di questo studio è la scrittura di una procedura che localizza accuratamente eventi sismici in tempo reale. La qualità delle localizzazioni è fortemente dipendente dalla corretta determinazione delle fasi P ed S. A volte è difficile riconoscere il corretto arrivo di una fase, poiché il segnale sismico può essere di difficile lettura per differenti motivi, come, ad esempio, la complessità del meccanismo della faglia generatrice e la presenza di rumore sia naturale che artificiale. Per questo motivo abbiamo studiato, analizzato e comparato differenti metodi per la rilevazione delle fasi e per la localizzazione degli eventi sismici. Gli algoritmi di rilevazione delle fasi che sono stati valutati sono lo Short Time Average su Long Time Average ratio (STA/LTA) e la funzione di Akaike Information Criterion (AIC). Il primo di questi è una tecnica comune usata per distinguere il segnale sismico dal rumore. E’ basato sul calcolo continuo di due valori medi dell’ampiezza assoluta di un segnale sismico in due finestre di tempo di differente lunghezza: media sull’intervallo breve (STA) e media sull’intervallo lungo (LTA). Il rapporto di queste due medie (STA/LTA) viene comparato ad un valore di soglia. Quando questo rapporto è maggiore della soglia, viene rilevata una fase nel segnale sismico analizzato. Il settaggio di questo sistema dipende dalla scelta dei parametri, questo prouce instabilità. La funzione di AIC è una metodologia sofisticata e precisa [Akaike and Hirotugu, 1974], basata sul classico metodo della massima verosimiglianza. La sua applicazione più comune consiste nella selezione tra pi` modelli: la stima della massima verosimiglianza dei parametri del modello da il minimo della funzione AIC. Questo metodo è strettamente correlato alla scelta della finestra di tempo nella quale applicare la funzione. Per questo motivo è necessaria una combinazione di più tecniche in modo da poter scegliere automaticamente la finestra corretta. In un segnale sismico il minimo della funzione AIC identifica l’arrivo delle onde P o delle onde S. Questa funzione è utilizzata nella procedura dell’AutoPicker [Turino et al., 2010]. Una volta identificate le fasi, è necessario elaborarle in modo da poter localizzare eventi sismici. In Antelope la procedura di localizzazione è chiamata orbassoc. Questa metodologia legge le fasi rilevate tramite il metodo STA/LTA e cerca di produrre una localizzazione dell’evento sulle tre possibili griglie: telesismica, regionale e locale. La soluzione, che produce tempi teorici di percorrenza per ogni stazione, che si accordano maggiormente con le osservazioni, viene considerata la migliore. Nell’AutoPicker l’algoritmo di localizzazione è Hypoellipse [Lahr, 1979], nel quale i tempi di percorrenza sono stimati utilizzando una struttura a strati piani paralleli e gli ipocentri sono calcolati utilizzando il metodo di Geiger [Geiger, 1912]. In questo lavoro abbiamo utilizzato metodologie per la localizzazione diverse da quelle assolute come Hypoellipse. L’HypoDD [Waldhauser and Ellsworth, 2000] è un algoritmo relativo, ovvero le localizzazioni vengono calcolate in riferimento alla localizzazione di un evento principale o dal sito di una stazione. Questo metodo può essere applicato solo nel caso in cui la distanza ipocentrale tra i due terremoti è piccola comparata alla distanza evento-stazione e alle eterogeneità laterali del campo delle velocità. In questi casi il percorso del raggio tra le due sorgenti e una stazione comune sono simili per gran parte del percorso del raggio. Per testare le prestazioni dell’AutoPicker, lo abbiamo applicato ad un database di 250 eventi registrati nell’area di contatto tra le Alpi e le Dinaridi nell’anno 2011 dalla rete C3ERN - the Central Eastern European Earthquake Reasearch Network [Dipartimento di Matematica e Geoscienze (DMG), Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), Agencija RS za okolje (ARSO) e Zentralanstalt fr Meteorologie und Geodynamik (ZAMG)]. L’algoritmo automatico proposto è risultato essere un utile strumento per l’assegnazione automatica degli arrivi delle onde P ed S. Questo risultato incoraggiante ci ha permesso di procedere nel confronto tra questa nuova metodologia e Antelope, utilizzato da noi quotidianamente in tempo reale per rilevare fasi e localizzare eventi. La complessità del contesto tettonico influenza il percorso dei raggi e conseguentemente la localizzazione degli eventi. In regioni dove sono presenti molte strutture sismogenetiche, una localizzazione precisa della sequenza sismica è essenziale, in modo da capire quale è la faglia generatrice. In questi casi l’uso di modelli 1-D potrebbe non essere sufficiente, mentre un modello 3-D potrebbe descrivere al meglio l’area interessata. La tomografia dei primi arrivi è una tecnica comune per ottenere un modello tridimensionale dalla localizzazione degli eventi. In questo studio abbiamo utilizzato una tomografia di eventi locali (Local Earthquake Tomography, LET) [Aki, 1982]. La tomografia dei primi arrivi e la localizzazione 3-D degli eventi sono state eseguite, rispettivamente, utilizzando il Computer Aided Tomography per modelli 3D (Cat3D) [Cat3D user manual, 2008] e il Non Linear Location (NonLinLoc) [Lomax et al., 2000] attraverso una procedura iterativa. Il Cat3D viene utilizzato solitamente in sismica attiva, mentre in questo studio è stato applicato ad un caso sismologico. La principale differenza tra la sismica attiva e la sismologia sono le incertezze nel sistema tomografico. Nella sismica attiva la localizzazione della sorgente è ben definita mentre nella sismologia è una variabile con incertezza elevata che si propaga nella stima del percorso del raggio e dei tempi di percorrenza. Per risolvere questo problema, abbiamo utilizzato una procedura iterativa composta dalla tomografia dei primi arrivi e dalla rilocalizzazione degli eventi con il modello 3-D risultante. Dopo il verificarsi della sequenza sismica emiliana nel Maggio-Giugno 2012, abbiamo deciso di analizzarla come interessante caso di studio. La sequenza sismica è iniziata il 20 Maggio (02:03:53 UTC), con un terremoto di Ml 5.9 [Scognamiglio et al., 2012]. Questa sequenza è composta da migliaia di eventi, sei dei quali con Ml maggiore di 5.0, tra cui un evento di magnitudo locale 5.8, il 29 Maggio (07:00:03 UTC). Su questi eventi abbiamo testato le prestazioni dell’AutoPicker e di Antelope. Per fare ciò abbiamo rilevato manualmente le fasi e localizzato alcuni degli eventi maggiori della sequenza sismica. Questi eventi sono caratterizzati da fasi P, ma in particolar modo fasi S, difficili da rilevare, probabilmente a causa del complesso meccanismo di faglia. Inoltre la complessità del sistema tettonico assieme all’incertezza della profondità focale rendono problematiche le localizzazioni degli eventi. La sequenza sismica emiliana ha interessato un’area di 50 km con andamento E-W localizzata nell’angolo sud della Pianura Padana, interessando il settore centrale dell’arco di Ferrara appartenente al sistema esterno della cintura degli Appennini Settentrionali. L’arco di Ferrara è composto da due sistemi: le pieghe di Ferrara nel nordest e la piega di Mirandola localizzata nella parte più interna a sudovest [Govoni et al., 2014]. Abbiamo elaborato gli arrivi P ed S in modo da poter localizzare la sequenza sismica utilizzando differenti modelli di velocità trovati in letteratura: Bragato et al. [2011], Ciaccio and Chiarabba [2002],Costa et al. [1992], Iside, Zollo et al. [1995], Malagnini et al. [2012], Massa [2012] e quattro modelli geologici proposti da Lavecchia et al. [in prep.] L’idea è di produrre un insieme di localizzazioni di eventi clusterizzati con residui minimi, in modo da poter capire quale è la faglia generatrice. Questo lavoro è stato svolto in collaborazione con l'Università di Chieti e il Dipartimento di Protezione Civile (DPC). Dalla distribuzione ipocentrale delle soluzioni, sembra che l'arco di Mirandola non sia coinvolto nella sequenza sismica, mentre i segmenti della parte interna e centrale del sistema di sovrascorrimento di Ferrara sembrano essere stati attivati dalle sequenze sismiche del 29 e del 20 Maggio, rispettivamente. La complessità dell'area interessata dalla sequenza sismica dell'Emilia, richiede il calcolo di modelli tridimensionali di velocità in modo da poter localizzare più precisamente gli eventi. Come già detto, abbiamo elaborato una procedura iterativa: tomografia dei primi arrivi e localizzazioni 3-D degli eventi, attraverso l'uso rispettivamente del Cat3D e del NonLinLoc, in collaborazione con l'OGS. La sequenza sismica copre solo una piccola parte della regione (30x30 km^2 di larghezza e 20 km di profondità), per questo l'area investigata si limiterà alla porzione superiore della crosta. Come modelli iniziali di velocità abbiamo scelto: Costa et al, 1992; Massa et al. 2013 e NewModel1 (LaVecchia et al., in prep., i quali avevano errori verticali inferiori al chilometro nello studio precedente. Il miglior modello iniziale sembra essere quello di Massa et al. (2013), il quale mostra valori di rms bassi rispetti alle altre soluzioni. I tre modelli tridimensionali di velocità per le onde P risultanti mostrano caratteristiche comuni: uno strato superficiale a bassa velocità e uno strato spesso (5-20 km in profondità) a 5.5km/s. I risultati tomografici per i modelli Vs presentano un comune strato superficiale a bassa velocità e uno strato caratterizzato da valori di velocità per le onde S di 3.0 km/s. Le tre serie di soluzioni, dei differenti modelli di velocità, sono comparabili all'interno dell'intervallo di errore, anche in termini di qualità. Le localizzazioni per la scossa principale del 20 maggio 2012 sono sparpagliate rispetto a quelle della seconda scossa principale del 29 maggio. Una possibile causa potrebbe essere l'installazione delle stazioni temporanee nel campo vicino della sequenza sismica dopo il 20 maggio 2012. Per l'evento del 29 maggio, infatti, si hanno molte più registrazioni che per il primo evento del 20 e tutte in campo vicino. Le localizzazioni degli eventi ottenute da modelli tomografici tridimensionali sono meno disperse di quelle ottenute con modelli unidimensionali, anche se le localizzazioni dei due eventi principali sono simili. In profondità le due serie di soluzioni non differiscono in modo significativo. Per migliorare la qualità della procedura di localizzazione nel nostro centro di raccolta dati, vorremo installare una procedura automatica sia rapida sia precisa. Per raggiungere questo risultato abbiamo comparato l'AutoPicker con Antelope sulla sequenza sismica dell'Emilia. Questo confronto è di fondamentale importanza per comprendere quale dei due algoritmi rileva fasi e/o localizza eventi in modo più preciso. Il nostro scopo, infatti, è quello di unire ed implementare queste due tecniche in modo da ottenere un miglior rilevatore di fasi e localizzatore. I risultati di questo confronto ci hanno portato a concludere che l'AutoPicker trova più fasi e con maggior precisione rispetto ad Antelope, sia per le fasi P che per le fasi S. Nonostante ciò il processo di associazione delle fasi in Antelope è in grado di correggere gli errori delle fasi e trovare la corretta localizzazione dell'evento. Questo ci ha suggerito di implementare l'algoritmo dell'AutoPicker nella procedura di Anteope, in modo tale che l' AutoPicker definisca gli arrivi P ed S e Antelope li associ e localizzi gli eventi. Con il miglioramento delle reti sismiche e la possibilità di raccogliere enormi quantitativi di dati, è necessario produrre enormi database, in modo da poter avere un rapido accesso ad essi e di poterli rielaborare in tempo reale o quasi reale. Per questi enormi database la rilevazione manuale delle fasi è un lavoro oneroso, che richiede tanto tempo. La possibilità di avere uno strumento che rilevi automaticamente fasi di ottima qualità, che producano risultati similari a quelli ottenuti dall'inversione tomografica utilizzando le fasi rilevate manualmente, è sicuramente conveniente ed utile. Per questa ragione abbiamo confrontato due differenti tomografie dei primi arrivi, prodotte con la stessa tecnica dell'analisi precedente, che differiscono solo per i dati di partenza: la prima è stata ottenuta dalle fasi rilevate manualmente, la seconda dalle fasi rilevate automaticamente con l'AutoPicker per la sequenza sismica dell'Emilia. I risultati ottenuti indicano un incremento del valore medio dell' rms sia nelle localizzazioni sia nella tomografia per le fasi automatiche. Nonostante questo i modelli tridimensionali ottenuti ( Vp, Vs and Vp/Vs) sono comparabili. Pertanto sembra che gli errori nelle localizzazioni non influenzino i risultati tomografici ma inficino la precisione del sistema tomografico stesso. Quindi per database contenenti enormi quantità di dati è possibile utilizzare le fasi automatiche come dati di partenza, ottenendo risultati comparabili a quelli ottenuti con le fasi manuali.
Earthquakes constitute a recurring natural disaster all over the Italian territory, and therefore civil defence focused interventions are extremely important. The rapidity of such interventions strongly depend on the production of fast and possibly real-time locations of the seismic events. The precise location of events is also needed to identify seismogenic faults. For these two aspects, an upgrade of the existing monitoring systems is fundamental to improve the automatic locations quality in a quasi real-time mode. The main purpose of this study is the production of a routine that will accurately locate seismic event in real-time. The quality of the locations strongly depends on the correct determination of the P- and S- phases. Sometimes it is hard to recognize the correct onset of a phase, since the signal can be blurred by various causes, such as, e.g., the complexity of the generating fault mechanism and the presence of natural or man-made noise. For this reason we have studied, analyzed and compared different phase picking and location methods. The picking algorithms that were evaluated are the Short Time Average over Long Time Average ratio (STA/LTA) and the Akaike Information Criterion (AIC) function. The first one is a common technique used to distinguish the seismic signal from noise. It is based on the continuous calculation of the average values of the absolute amplitude of a seismic signal in two moving-time windows with different lengths: the short-time average and the long-time average. The STA/LTA ratio is compared with a threshold value. When the ratio is larger than this threshold, the onset of a seismic signal is detected. The main disadvantage of this method is its instability, due to the parameters choice: a too long STA window could cause the non-detection of local events, whereas a too short STA window could cause the detection of man-made seismic noise. A high STA/LTA threshold records less events than the ones those have occurred, but false triggers are eliminated. If this value is chosen to be lower, more events will be detected, but more frequent false triggers could be recorded. This algorithm is part of the Antelope (BRRT, Boulder) detection procedure, used in this study. The AIC function is a precise and sophisticated methodology, being a revision of the classical maximum likelihood estimation procedure (Akaike, 1974). The AIC function is designed for statistical identification of model characteristics. Its most classical application consists in the selection of the best among several competing models; the maximum likelihood estimate of the model parameters gives the minimum of AIC function. It is strictly correlated to the correct choice of the time window in which apply the function, so it is necessary combined with other techniques, in order to automatically choose a correct window. This dependence on other methods, makes the application of the AIC function to detect phases, a complex methodology, which can be affected by errors in the parameter choices. The AIC function is used in the AutoPicker procedure (Turino et al., 2012). In a seismic signal the minimum of the AIC function identifies the P- or S- onset. In this automatic phase picker the time window in which to apply the function, in the case of P phases, is chosen by a combination of a band-pass filter and an envelope time function, used as “energy” detector to select the event in the waveform; for the S phases, the selection of the window is guided by a preliminary location of the P- phases. Once the P- and S- phases are identified, it is necessary to elaborate them in order to locate the seismic event. In Antelope the location procedure is called orbassoc. This methodology reads the pickings, determined through the use of the STA/LTA technique, and tries to produce an event location over three possible grids: teleseismic, regional and local. The solution that produces the minimum travel time residuals set (differences between synthetic travel times and observed travel times) is considered as the best one. In the AutoPicker the location algorithm is Hypoellipse (Lahr, 1979), in which the travel-times are estimated from a horizontally-layered velocity-structure and the hypocenter is calculated using Geiger's method (Geiger, 1912) to minimize the root mean square (rms) of the travel time residuals. In order to improve the location quality we have used in this work various location methodologies with respect to the absolute ones, such as Hypoellipse. The HypoDD (Waldhauser et al., 2000) is a relative algorithm, the locations depend either on the location of a master event or on a station site. This method can be applied only in the case when the hypocentral separation between two earthquakes is small compared to the event-station distance and the scale length of the velocity heterogeneities. In such cases the ray paths between the source region and a common station are similar along almost the entire ray path. In order to test the performances of the AutoPicker, we have applied it to a database of 250 events recorded in the year 2011 by the C3ERN - the Central Eastern European Earthquake Reasearch Network [Department of Mathematics and Geosciences (DMG), Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), Agencija RS za okolje (ARSO) and Zentralanstalt für Meteorologie und Geodynamik (ZAMG)] – at the Alps-Dinarides contact. The proposed automatic picker appears to be a useful tool for assigning automatically onset P and S times to detected seismic signals for the purpose of rapid hypocenter calculations. These encouraging results have allowed us to proceed comparing this new picking methodology to another one, tested and used daily and in real-time by us to detect and locate events, the Antelope software. The complexity of the tectonic environment influences ray tracing and consequently the event locations. In regions where many seismogenic structures are present, a precise location of a seismic sequence is essential, in order to understand which fault is the generating one. In such cases the use of a 1-D velocity model might not be sufficient, so a 3-D velocity model is a better solution to describe the studied area. The travel-time tomography is a common technique to obtain a 3-D velocity model, from event locations. In this study we have chosen a local earthquake tomography (LET) (Aki, 1982). The travel time tomography and the 3-D event location are performed, respectively, using the Computer Aided Tomography for 3D models (Cat3D) software (Cat3D manual, 2008) and the Non Linear Location (NonLinLoc) software (Lomax et al., 2000) through an iterative procedure. The Cat3D is basically used in active seismics, but in this study it is applied to a seismological case. The main difference between active seismics and seismology are the unknowns in the tomographic system. In seismology the source location is an unknown parameter with a high uncertainty, while in active seismics the source locations are well defined. In this study, the introduction of the source location in the tomographic system, introduces uncertainties in obth the ray tracing and travel-times estimation. In order to solve this uncertainty, we used an iterative procedure composed by the application of tomography and the event location in resulting 3-D velocity model. After the occurrence of the Emilia seismic sequence in May-June 2012, we have decided to investigate it as an interesting study case. The sequence started on May 20 (02:03:53 UTC), with a ML 5.9 earthquake, preceded by a M_L 4.1 foreshock, three hours earlier (Scognamiglio et al., 2012). Theaftershock sequence comprised thousands of earthquakes, six of them with M_L ≥ 5.0. Among these, a M_L 5.8 earthquake, on May 29 (07:00:03 UTC), caused probably more damages than the first shock. Through the study of this seismic sequence we have tested the performances of the automatic picking algorithms. In order to do that, we have manually picked and located some of the major events of this seismic sequence. These events are characterized by P- and especially S-phases, which are really difficult to detect, probably because the fault system of the Emilia earthquake area is complex. Moreover, the complexity of the tectonic environment along with the focal depth uncertainty make the event locations problematic, because it is not always easy to assess which fault has moved. The Emilia sequence occurred in the central, roughly E-W trending, sector of the Ferrara arc belonging to the external fold-and-thrust system of the Northern Apennines belt. The Ferrara arc is structured into two major fold-and-thrust systems: the Ferrara system in the northeast and the Mirandola system located in a more internal position to the southwest (Govoni et al., 2014). We have processed the P- and S- onsets in order to locate the seismic sequence using different velocity models found in literature: Bragato et al. (2011), Ciaccio et al. (2002), Costa et al. (1992), “Iside”, Zollo et al. (1995), Malagnini et al. (2012), Massa (Rapporto DPC-INGV S1-2013) and four geological models proposed by Lavecchia et al. (in prep). The idea is to produce a set of clustered event locations with the lowest residuals, in order to understand which is the generating fault in the complex system of faults. This work is being performed in collaboration with Università di Chieti and Department of Civil Defence (DPC). From the hypocentral distribution, it seems that the Mirandola thrust was not involved during the Emilia sequence, whereas the internal and middle segments of the Ferrara thrust systems were activated by 29 and 20 May seismic sequences, respectively. The complexity of the seismic sequence area in Emilia requires the calculation of a tridimensional velocity model in order to locate more precisely the events. As already said, we elaborated an iterative procedure: travel-time tomography and 3-D event locations, through the use of the Cat3D and NonLinLoc softwares, in collaboration with OGS. This is done to minimize the uncertainties introduced in the tomographic system by the unknown source locations. Since the seismic sequence covers only a small part of this region (about 30x30km^2 wide and 0-20 km deep), the investigated area will be limited to its upper crustal part. As initial velocity models, we have chosen those ones: Costa et al, 1992; Massa et al. 2013 and NewModel1 (LaVecchia et al., in prep.) that have vertical errors lower than one km. The best velocity model is the one, obtained using as initial model the Massa et al. (2013), which shows rms values lower than the others. The three resulting 3-D Vp velocity models shows similar characteristcs: a surface layer (0 – 5 km) of low Vp velocity, about 1,8 km/s, and a thick layer (5 – 20 km) of 5.5 km/s. The tomographic results for Vs velocity model present a common shallow layer (0 - 3 km) of low velocity (about 1 km/s) and a thick layer (3 - 13 km) characterized by a Vs velocity value of about 3.0 km/s. The three set of solutions, from the different velocity models, are comparable in the errors range. The locations for the main-shock of the 20th of May, 2012 are more scattered respect the solutions for the 29th's. A possible reason could be the installations of temporary stations in the near field of the sequence after the 20th of May, 2012. For the 29th event, in fact, we have more waveforms than for the previous main-shock, and all of them in the near field. We calculated the rms for each event in order to discriminate a velocity model with respect to another from the quality of the locations. We obtained three similar rms values trends, so we were not able to choose a best velocity model. The events locations from 3-D tomographic models are less scattered than those one computed from the 1-D ones; otherwise the locations of the two main-shock events seem to be quite similar. In depth the two set of solutions do not differ in a significative way. To improve the quality of the location procedure in our datacenter, we would like to install a precise and rapid automatic procedure. Therefore, we have compared the AutoPicker method with a more tested and solid one, the Antelope picking method, on the Emilia seismic sequence of data, using as reference pickings and locations the manual ones. This comparison is of fundamental importance which one of the two algorithms better detects phases and/or locates events. Our aim is, in fact, to merge and implement these two techniques to obtain a better detector and locator. AutoPicker finds more and preciser phases than Antelope both P- and mainly S-phases. Despite that the associator process in Antelope, is able to correctly associate the detections and to find the correct location. The obtained results suggest us to implement the AutoPicker algorithm in the Antelope procedure in order to use the AutoPicker to define P- and S-onset and Antelope to associate them and locate the events. With the improvement of seismic networks and the possibility to store huge amounts of data, it is necessary to produce big databases, in order to have a rapid access to the data and to re-elaborate them in real time o quasi real time mode. For big databases, the manual picking is an onerous work, requiring a lot of time. The possibility to have a good-quality automatic tool for phase recognition and picking, which produces similar results to those obtained from the tomographic inversion by using manual phases picking, is certainly convenient and useful. For this reason, we have compared two different travel time tomographic inversions made with the same technique of the previous analysis, differing only in the input phase files: the first one obtained from manual pickings, the second one from the automatic AutoPicker pickings of the Emilia sequence. The obtained results indicate an increase of the average rms both on the locations and on the tomography. Despite that, the tridimensional velocity models (Vp, Vs and Vp/Vs) are comparable, therefore, it seems that the location errors do not influence the tomographic results but the precision of the tomographic system. So for a large database it is possible to use automatic phases as input in a travel-time tomography, obtaining similar results as those obtained using manually picked phases.
XXVI Ciclo
1985
Han, Liang. "Seismic imaging and thermal modeling of active continental rifting processes in the Salton Trough, Southern California." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/78906.
Повний текст джерелаPh. D.
Mihoubi, Abdelhafid. "Imagerie sismique de la structure profonde de la marge Algérienne orientale (secteur de Jijel) : implications en terme de potentiel pétrolier." Thesis, Brest, 2014. http://www.theses.fr/2014BRES0037/document.
Повний текст джерелаThis thesis has been conducted within the framework of the Algerian-French research cooperation program SPIRAL (Sismique Profonde et Investigations Régionales du Nord de l’Algérie). This project aims to study the deep structure of the Algerian margin. The area covered by this study focuses in the region of Jijel in eastern Algerian margin.The main objective of our thesis is to improve depth imaging of the Algerian margin using a combined approach of seismic techniques; wide-angle and multi- channel seismic data. The purpose of this thesis is to bring new knowledge to answer some questions about the nature of the crust, the area of continental -oceanic transition, the presence of Messinian salt, its distribution and relationship between surface sedimentary formations and crustal structures.This study presents the results of a deep seismic survey across the north Algerian margin, based on the combination of 2D multi-channel and wide-angle seismic data simultaneously recorded by 41 ocean bottom seismometers deployed along a North-South line extending 180 km off Jijel into the Algerian offshore basin, and 25 land stations deployed along a 100 km-long line, cutting through the Lesser Kabylia and the Tellian thrust-belt.In this study, our approach is a joint inversion of wide-angle seismic recordings (OBS, ocean bottom seismometers) and multi- channel seismic data (MCS). We conducted a series of first arrivals tomography, a joint inversion of reflected and refracted arrivals and gravity modelling. Since the solution of the inverse problem is not unique, two tomography programs were applied using the same data for the same study area; FAST (First Arrival Seismic Tomography) and Tomo2D. Tomography was followed by a joint inversion of reflected and refracted arrivals following an approach based on the combination of Kirchhoff prestack depth migration (PSDM) for MCS data and forward modelling of OBS. To check the consistency of the velocity model with gravity data, the free air anomaly was modeled.The final model obtained using forward modelling of the wide-angle data and pre-stack depth migration of the seismic reflection data provides an unprecedented view of the sedimentary and crustal structure of the margin. The sedimentary layers in the Algerian basin are 3.75 km thick to the north and up to 4.5 to 5 km thick at the foot of the margin. They are characterised by seismic velocities from 1.9 km/s to 3.8 km/s. Messinian salt formations are about 1 km thick in the study area, and are modelled and imaged using a velocity between 3.7 km/s to 3.8 km/s. The crust in the deep sea basin is about 4.5 km thick and of oceanic origin, presenting two distinct layers with a high gradient upper crust (4.7 km/s - 6.1 km) and a low gradient lower crust (6.2 km/s - 7.1 km/s). The upper mantle velocity is constrained to 7.9 km/s. The ocean-continent transition zone is very narrow between 15 km to 20 km wide. The continental crust reaches 25 km thickness as imaged from the most landward station and thins to 5 km over a less than 70 km distance. The continental crust presents steep and asymmetric upper and lower crustal geometry, possibly due to either asymmetric rifting of the margin, an underplated body, or flow of lower crustal material towards the ocean basin. Present-time deformation, as imaged from 3 additional seismic profiles, is characterized by an interplay of gravity-driven mobile-salt creep and active thrusting at the foot of the tectonically inverted Algerian margin
Bazin, Sara. "Three-dimensional crustal structure of East Pacific rise discontinuities from tomographic inversions /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2000. http://wwwlib.umi.com/cr/ucsd/fullcit?p3035403.
Повний текст джерелаAraujo, Sebastián. "Travel time tomography of the crust and the mantle beneath Ecuador from data of the national seismic network." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAU015/document.
Повний текст джерелаAlthough there have been numerous studies on the geodynamics and the tectonics in Ecuador based on the seismic activity, there has not been to date a comprehensive tomography study using the entire database of the National Seismic Network (RENSIG). Only a preliminary limited study was performed by Prevot et al. to infer a simple P velocity model in central Ecuador, and several profiles in the South-Colombian-Ecuador margin were also investigated by using travel time inversion of wide-angle seismic data obtained during the two marine experiments SISTEUR and SALIERI. Inverting the hundreds of thousands of arrival times of P and S waves of uneven quality that constitutes the RENSIG catalogue is the challenging subject of this thesis.We describe how we complemented the RENSIG catalogue with data from the Northern Peru network and how we homogenized and filtered the resulting dataset of more than 800 000 first arrival times of P and S waves corresponding to more than 50 000 earthquakes. To invert these data for both the velocity models and the event locations we adopted a Bayesian approach. We show how the problem can be recast in the Gaussian framework by changes of variable while imposing a robust statistics to the data, and how it leads to a generalized nonlinear least squares problem. We detail in particular the regularization of the models through the smoothing and damping properties of the covariance kernels. We also show that inverting differences in data instead of the raw data amounts to the introduction of specific correlation terms in the data covariance matrix, while keeping the same set of data. We finally indicate how the computation of the averaging index allows the delimitation of a confidence region for the resulting model.The practical inversion has been carried out by using the two Fortran 2003 codes (B. Potin, B. Valette, V. Monteiller): LOCIN (prior localization) and INSIGHT (tomography). The final study region is a parallelepipedic box of 590$times$770 km$^2$ area and 244 km height that contains the topography of the surface. The models consist of the $v_P$ and $v_P/v_S$ fields discretized over a grid, the spacing of which is 5 km in the horizontal directions and 2 km in the vertical one, and of the spatial and temporal parameters of the seismic events. A battery of tests allowed us to set reasonable values for these tuning parameters through an L-curve analysis.We obtained the spatial distribution of the seismicity with an improved accuracy which allows us to describe with more details the shallow seismic clusters, as those of Pisayambo, Macas, Reventador, and to identify lineaments in the seismicity in relation with tectonics. We obtained also a clear image of the intermediate depth seismicity wich is dominated by 4 nests, namely the Maldonado, La Man'a, and Guayaquil nests, at depths ranging between 75 km and 115 km, and the Puyo nest at much deeper depths. The Wadati-Benioff zone allowed us to clearly defined the topography of the slab only to a depth to about 110-150 km, depending on the latitude, and to observe the decrease of the dip angle from about 25° in northern and central Ecuador down to about 10° in southern Ecuador and northern Peru. On the other hand, the analysis of the P velocity clearly suggests that the slab is broken in two pieces, the southern one passing under the northern at the level of the Puyo nest. The $v_P/v_S$ model presents a high anomaly of the ratio along the western cordillera at a depth ranging between 30 km and 50 km that characterized partially melted rocks and corresponds to the feeding reservoir of the volcanic arc. Finally, we deduced the Moho depth from our model by taking the depth for which the norm of the velocity gradient is maximum between 7.2 and 7.4 km/s and by incorporating information on the Moho depth provided by the SISTEUR and SALIERI experiments in the convergent margin
Macquet, Marie. "Tomographie crustale des Pyrénées et des régions avoisinantes par corrélation de bruit." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENU037/document.
Повний текст джерелаIn this thesis, we applied the ambient noise correlation method in the very heterogeneous region of the Pyrenees and the surrounding areas (mountain belt and thick sedimentary basins). The dataset used is a combination of two temporary broadband arrays from France and Spain (PYROPE and IBERARRAY) and stations of the French and Catalan permanent broadband arrays. Seismic noise recorded over years by the 158 stations was used to calculate correlations in a period range of 5-55 s. Observed Rayleigh and Love wave group velocities between pairs of stations were used as input to a linearized inversion scheme, where we obtained for each period group velocities maps, with a lateral resolution of approximately 40 km. The comparison between the two type of waves demonstrates radial anisotropy at short periods, while little or no radial anisotropy is present at long periods. We developed a new strategy for the inversion of dispersion curves to shear wave velocity models and applied it to the Rayleigh waves group velocity. This approach is based on the combination of a full exploration of the model space and a linearized inversion. The obtained model, validated by the comparison of our results with the results of other methods, is the first complete 3-D crustal Vs model of the region. We in particular note : (1) Atypical S-waves profiles in the Eastern part of the Massif Central which indicate a thinned crust and low velocities in the uppermost mantle. (2) High-velocity anomalies at 25 km depth beneath the Labourd-Mauléon area and the on-land continuation of the Parentis basin. We suggest that they are the traces of the hyper-extension which might have preceded the collision phase which lead to the formation of the Pyrenees. The strong heterogeneity of our study region is also well-adapted to analyze the influence of the ray deviations on the reconstruction of the model. First results show that the reconstructed model, using great-circle paths, does not explain the ray deviations as observed by beamforming. Observed deviations therefore carry the potential of improving the model in a combined inversion scheme
Lecomte, Isabelle. "Structure crustale d'une dorsale lente : tomographie sismique 3D sur la dorsale de Mohn (72°20N, 1°30E)." Université Louis Pasteur (Strasbourg) (1971-2008), 1990. http://www.theses.fr/1990STR1A003.
Повний текст джерелаHuang, Hui Ph D. Massachusetts Institute of Technology. "Ambient noise tomography for wavespeed and anisotropy in the crust of southwestern China." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/87518.
Повний текст джерелаCataloged from PDF version of thesis.
Includes bibliographical references.
The primary objective of this thesis is to improve our understanding of the crustal structure and deformation in the southeastern Tibetan Plateau and adjacent regions using surface wave tomography. Green's functions for Rayleigh and Love waves are extracted from ambient noise interferometry. Using the Green's functions, we first conduct traditional traveltime tomography for the two shear wavespeeds Vsv and Vsh Their differences are measured as radial anisotropy. We then conduct Eikonal tomography to study azimuthal anisotropy in the crust. Our tomography results are well consistent with geology in the study region. In the Sichuan Basin, low wavespeed and positive radial anisotropy (Vsh> Vsv) in the upper crust reflect thick sedimentary layers at surface; high wavespeed and small radial anisotropy in the middle and lower crust reflect a cold and rigid basin root. Little azimuthal anisotropy is observed in the Basin, indicating small internal deformation. In the Tibetan Plateau, we observe widespread low wavespeed zones with positive anisotropy in the middle and lower crust, which may reflect combined effects of weakened rock mechanism and horizontal flow in the deep crust of southeastern Tibet. The northern part of the Central Yunnan block, which geographically coincides with the inner zone of the Emeishan flood basalt, reveals relatively higher wavespeeds than the surrounding regions and little radial anisotropy throughout the entire crust. We speculate that the high wavespeeds and small radial anisotropy are due to combined effects of the remnants of intruded material from mantle with sub-vertical structures and channel flow with sub-horizontal structures. In general, the azimuthal anisotropy in our study region is consistent with a clockwise rotation around the Eastern Himalayan Syntaxis. Careful examination reveals large angular differences between the azimuthal anisotropy in the upper and lower crust, suggesting different deformation patterns at the surface and in depth. Therefore, our tomography results support models with ductile flow in the deep crust of the southeastern Tibetan Plateau; however, the large lateral variation of both wavespeeds and anisotropy indicates that the flow also varies greatly in intensity and pattern in different geological units.
by Hui Huang.
Ph. D.
Saygin, Erdinc, and erdinc saygin@anu edu au. "Seismic Receiver and Noise Correlation Based Studies in Australia." The Australian National University. Research School of Earth Sciences, 2007. http://thesis.anu.edu.au./public/adt-ANU20091009.115242.
Повний текст джерелаWagner, Diana [Verfasser]. "Tomographic investigation of the crust of Central Java, Indonesia / Diana Wagner." Kiel : Universitätsbibliothek Kiel, 2008. http://d-nb.info/1019754621/34.
Повний текст джерелаSun, Youshun 1970. "P- and S- wave tomography of the crust and uppermost mantle in China and surrounding areas." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33172.
Повний текст джерелаThis electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references.
This thesis involves inverting the seismic structure of the crust and uppermost mantle in China from the P- and S-wave travel-time tomography. The main contributions of this research are: 1) introducing the adaptive moving window method to obtain 2338 1D P and S models in China; 2) introducing a tomographic method to perform the 3D body wave travel-time tomography with the Moho discontinuity included. Both horizontal and vertical resolutions are highly controlled and smooth transitions among adjacent locations are guaranteed in the final models. To achieve these objectives, the Monte-Carlo (random search) method and the Gauss-Newton method are applied iteratively to find the nonlinear least square solutions and to optimize the models in the crust and uppermost mantle. The models we obtained provide accurate travel-time calculation, ground-truth event relocation and seismogram fittings. These models can therefore be applied to reliable earthquake location. Geological, geodynamic, and volcanic implications of our models are discussed in this thesis. Our tomographic models provide new insights into the geological structure and tectonics of the region, such as lithological variations and large fault zones across the major geological terranes.
(cont.) Compared with previous tomographic studies, we have used a larger, higher quality data set and applied an updated tomographic method to take into account the effects of the complex Moho geometry in this region. Our results cast a new light over the complex structure and seismotectonics of China and surrounding areas.
by Youshun Sun.
Ph.D.
Hubans, Fabien. "Utilisation des corrélations de bruit micro-sismique pour l'analyse des propriétés du champ d'onde et l'imagerie crustale." Phd thesis, Grenoble, 2010. http://tel.archives-ouvertes.fr/tel-00564324.
Повний текст джерелаGans, Christine. "Investigations of the Crust and Upper Mantle of Modern and Ancient Subduction Zones, using Pn Tomography and Seismic Receiver Functions." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/145719.
Повний текст джерелаOlsson, Sverker. "Analyses of Seismic Wave Conversion in the Crust and Upper Mantle beneath the Baltic Shield." Doctoral thesis, Uppsala University, Department of Earth Sciences, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7930.
Повний текст джерелаTeleseismic data recorded by broad-band seismic stations in the Swedish National Seismic Network (SNSN) have been used in a suite of studies of seismic wave conversion in order to assess the structure of the crust and upper mantle beneath the Baltic Shield. Signals of seismic waves converted between P and S at seismic discontinuities within the Earth carry information on the velocity contrast at the converting interface, on the depth of conversion and on P and S velocities above this depth.
The conversion from P to S at the crust-mantle boundary (the Moho) provides a robust tool to constrain crustal thicknesses. Results of such analysis for the Baltic Shield show considerable variation of Moho depths and significantly improve the Moho depth map. Analysis of waves converted from S to P in the upper mantle reveals a layered lithosphere with alternating high and low velocity bodies. It also detects clear signals of a sharp velocity contrast at the lithosphere-asthenosphere boundary at depths around 200 km.
Delay times of P410s, the conversion from P to S at the upper mantle discontinuity at 410 km depth, were used in a tomographic inversion to simultaneously determine P and S velocities in the upper mantle. The polarisation of P410s was also used to study anisotropy of the upper mantle. Results of these analyses are found to be in close agreement with independently derived results from arrival time tomography and shear-wave splitting analysis of SKS.
The results presented in this thesis demonstrate the ability of converted wave analysis as a tool to detect and image geological boundaries that involve sharp contrasts in seismic properties. The results also show that this analysis can provide means of studying aspects of Earth’s structure that are conventionally studied using other types of seismic data.
Ligdas, Constantina Nadia. "P-wave velocities in the crust and upper mantle of the Aegean area by tomographic inversion." Thesis, University of Reading, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.276207.
Повний текст джерелаGUMIAUX, Charles. "Modélisation du cisaillement hercynien de Bretagne centrale : déformation crustale et implications lithosphériques." Phd thesis, Université Rennes 1, 2003. http://tel.archives-ouvertes.fr/tel-00003938.
Повний текст джерелаMarot, Marianne. "Zones de subduction horizontale versus normale : une comparaison basée sur la tomographie sismique en 3-D et de la modélisation pétrologique de la lithosphère continentale du Chili Central et d’Ouest de l’Argentine (29°S-35°S)." Thesis, Nice, 2013. http://www.theses.fr/2013NICE4046/document.
Повний текст джерелаBeneath central Chile and western Argentina, the oceanic Nazca slab drastically changes geometry from horizontal to dipping at an angle of 30°, and correlates with the subduction of the Juan Fernandez seamount ridge. The aim of our study is to assess, using a thermo-petrological-seismological approach, the differences of the overriding lithosphere between these two regions, in order to better understand the deep structure of the continental lithosphere above the flat slab, and the links between the deformations at the surface and at depth. We show the most complete regional 3-D seismic tomography images of this region, whereby, in comparison to previous studies, we use (1) a much larger seismic dataset compiled from several short-term seismic catalogs, (2) a much denser seismic station network which enables us to resolve better the subduction zone. We show significant seismic differences between the flat and normal subduction zones. As expected, the flat slab region is impacted by colder temperatures, and therefore by faster seismic velocities and more intense seismic activity, compared to the normal slab region. We show evidence that the flat slab dehydrates within the mantle wedge, but also along the subducting ridge prior to re-subducting. The forearc crust above the flat slab is described by unusual seismic properties, correlated to the slab geometry at depth, and/or, to the aftershock effects of the 1997 Mw 7.1 Punitaqui earthquake which occurred two years before the recording of our events. The continental crust above the flat slab has very heterogeneous seismic properties which correlate with important deformation structures and geological terranes at the surface. We confirm previous studies that have shown that the thick lower crust of the present day Andean arc is non-eclogitized and maybe representing the felsic Chilenia terrane, whereas to the east, the Cuyania terrane in the backarc is more mafic and contains an eclogitized lower crust
Silvennoinen, H. (Hanna). "3D structure of the crust and upper mantle beneath Northern Fennoscandian shield." Doctoral thesis, University of Oulu, 2015. http://urn.fi/urn:isbn:9789526210681.
Повний текст джерелаNunn, Ceri. "Tomographic images of the crust and upper mantle beneath the Tibetan Plateau : using body waves, surface waves and a joint inversion." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708398.
Повний текст джерелаBouchet, Bert Manoz Romain. "Structure de la lithosphère continentale de l'Ouest USA : contribution des isotopes du Plomb,du Néodyme, et de l'Hafnium." Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2014. http://tel.archives-ouvertes.fr/tel-01066021.
Повний текст джерелаMontagner, Jean-Paul. "Etude de la structure profonde de la terre a partir des ondes de surface de longue periode." Paris 6, 1986. http://www.theses.fr/1986PA066188.
Повний текст джерелаGuilbert, Jocelyn. "Caractérisation des structures lithosphériques sous le Nord Tibet et sous le Massif Central à partir des données sismologiques du programme Lithoscope." Phd thesis, Université Joseph Fourier (Grenoble), 1995. http://tel.archives-ouvertes.fr/tel-00721900.
Повний текст джерелаDash, Ranjan Kumar. "Crustal structure and marine gas hydrate studies near Vancouver Island using seismic tomography." Thesis, 2007. http://hdl.handle.net/1828/2498.
Повний текст джерелаCheng, Ching-Yu, and 鄭璟郁. "3-D Shear Wave Shallow Crustal Structures at Meishan Fault Zone using Ambient Noise Tomography." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/fjq945.
Повний текст джерела國立中央大學
地球科學學系
105
1906 M7.1 Meishan earthquake occurred near Chiayi city in southwestern Taiwan and resulted in more than three thousands casualties and six thousands of buildings collapsed. Based on the geological survey, the Meishan fault zone a right-lateral strike-slip fault with a length of 25 kilometers, was the main contributor for this event. In previous studies, many researchers have done lot of investigation about the Meishan Fault zone, including geologic researches at surface and seismic explorations at shallow crust. However, there is still limited information about 3-D shallow crustal structure of this study area. Therefore, we deployed 100 Texan instruments (~2 km interval) between Aug. and Nov. 2015, covered around the Meishan Fault zone. We obtained a 3-D shear wave shallow crustal velocity structure using ambient noise tomography. The reliable periods of phase velocity from Rayleigh wave are 0.6 to 5.8 seconds, which correspond to around 0-5 km at depths. The results are consistent with surface geology and seismic explorations study. Furthermore, Meishan fault, Chiayi blind thrust, and Xiaomei anticline near the fault zone are observed from this study.
Stephenson, Andrew. "Crustal velocity structure of the Southern Nechako Basin, British Columbia, from wide-angle seismic traveltime inversion." Thesis, 2010. http://hdl.handle.net/1828/3145.
Повний текст джерелаCheng, I.-Hsiu, and 鄭亦修. "3-D Multi-scale Finite-frequency Ambient Noise Rayleigh Wave Tomography of Crustal S-Wave Velocity Structure beneath Central Tibet." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/70487862466898554989.
Повний текст джерела國立臺灣大學
地質科學研究所
101
Surface wave travel-time tomography has been widely used as a powerful strategy to image shear wave velocity structure of the Earth’s crust and upper mantle. Traditionally with either ray theoretical great-circle approximations or 2-D phase kernels, phase velocity maps are first obtained at multiple frequencies. They are then combined to invert for shear wave velocity structure using 1-D depth-varying Frechet derivatives of phase velocity with respect to shear wave speed. Such approach runs short on considering the directional- and depth-dependence of scattering while surface wave propagating through laterally heterogeneous Earth. We here present a fully 3-D finite-frequency method based on the Born scattering theory in conjunction with surface-wave mode summation and apply it to regional fundamental Rayleigh wave tomography in central Tibet. Our data were collected from Hi-CLIMB array in the central Tibet during 2004-2005. Following a standard procedure to obtain empirical Green’s functions of Rayleigh waves from ambient noise cross correlation functions (CCFs) between station pairs, the phase differences between the CCFs and corresponding synthetics are measured by a multi-taper cross-spectral method. We apply the 3-D sensitivity kernels at individual frequencies convolved with the same eigentapers used in the phase measurement to conduct a 3D tomography of shear wave velocity perturbations with respect to a spherically-symmetric earth model suitable for central Tibet. A wavelet-based, multi-scale parameterization is invoked in the tomographic inversion to deal with the intrinsic problem of unevenly distributed data and resolve the structure with data-adaptive spectral and spatial resolutions. The result shows that the crust is generally slower to the north of the Bangong-Nujiang Suture (BNS) in marked contrast to the south with higher speeds. The absence of pervasive low velocity anomalies in the mid-to-lower crust indicates that the ductile channel flow of the lower crust may be inactive beneath southern Tibet. The model resolution in the lithospheric mantle can be improved by integrating longer-period surface data from distant earthquakes, which will yield better constrains on the geodynamic process of the Himalayan-Tibetan orogeny.
Darlington, Andrea. "Geophysical constraints on mantle viscosity and its influence on Antarctic glacial isostatic adjustment." Thesis, 2012. http://hdl.handle.net/1828/4001.
Повний текст джерелаGraduate
Humphreys, Eugene Drake. "Studies of the crust-mantle system beneath Southern California." Thesis, 1985. http://catalog.hathitrust.org/api/volumes/oclc/30757542.html.
Повний текст джерелаSaygin, Erdinc. "Seismic Receiver and Noise Correlation Based Studies in Australia." Phd thesis, 2007. http://hdl.handle.net/1885/49353.
Повний текст джерелаChen, Kai-Xun, and 陳凱勛. "High-resolution 3-D Shear Wave Upper-crust Structures in Ilan Plain using Ambient Noise Tomography." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/09267432428593408826.
Повний текст джерела國立中央大學
地球科學學系
103
The Ilan Plain (IP) in NE Taiwan locates on the western end of the Okinawa trough and exhibits high geothermal gradients with abundant hot springs, likely resulting from magmatism associated with the back-arc spreading as manifested by the offshore volcanic island (Kueishantao)(Tong et al., 2008). North and south sides of IP are divided by Lan-Yang River with distinctive characteristics. Comparing to the northern part, the southern part exhibits, relatively, thin unconsolidated Quaternary alluvium layer with depths ranging from 0 to 1 km (Chiang, 1976), high on-land seismicity and significant SE movements relative to Penghu island. Purposes of this study are two folds. By obtaining a high-resolution 3-D shear wave upper-crust structures, we aim at (1) assessing the extent of underground geothermal sources as revealed by low velocity anomalies, (2) mapping 3-D sedimentary structures as revealed by the structures of very low velocity zones at surface. To fulfill this goal, we deployed 89 Texan instruments (~2 km station interval) between Aug. 2014 and Jan. 2015, covering most of the IP and its vicinity. We conduct methods of ambient noise tomography for inversion of high-resolution 3-D shear wave upper-crust velocity structures. Firstly, we estimate empirical Green’s functions (EGF) of Rayleigh wave between station pairs by ambient noise cross-correlation. Secondly, dispersion curves of group and phase velocities are measured at the frequency range between 0.25 and 1.67 Hz from each EGFs. Multiple filter Technique and Image transformation technique are used to measured group and phase velocities at each period, respectively. Finally, we apply a fast marching method for inhomogeneous-medium ray tracing and for calculations of velocities between station pairs. We also adopt a wavelet-based sparsity-constrained tomography method for the direct inversion of 3-D shear wave velocity structures. Results show that the lowest shear wave velocity can be as low as 0.4 km/s. mostly at depths shallower than 500 meters. Having examined the vertical cross-sections of each profiles, the spatial distributions of low velocity zones well match to those of sedimentary structures as shown by seismic reflection survey (Chiang, 1976). Results in west IP show that local low velocity anomalies with depth shallower than 1 km display in regions of known geothermal wells.
Liu, Kaijian. "Teleseismic Imaging of the Crust and Upper Mantle in the Western United States." Thesis, 2012. http://hdl.handle.net/1911/64700.
Повний текст джерелаPilia, Simone. "3-D tomographic imaging of the Southeast Australian crust : new insight into the evolution of the east Gondwana margin." Phd thesis, 2014. http://hdl.handle.net/1885/156207.
Повний текст джерелаKAVIANI, Ayoub. "La chaîn de collision continentale du Zagros (Iran): Structure lithosphérique par analyse de données sismologique." Phd thesis, 2004. http://tel.archives-ouvertes.fr/tel-00006897.
Повний текст джерелаKarousová, Hana. "Teleseismická tomografie svrchního pláště pod Českým masívem." Doctoral thesis, 2014. http://www.nusl.cz/ntk/nusl-328174.
Повний текст джерелаKolínský, Petr. "Analýza a inverze povrchových vln - aplikace na Český masiv." Doctoral thesis, 2010. http://www.nusl.cz/ntk/nusl-296110.
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