Volcanic earthquakes can provide significant insight into physical processes acting at volcanoes, such as magma accumulation and the mechanisms of deformation of the volcanic edifice. At the same time a statistical analyses of volcanic seismicity prior to an eruption (for example variations in the Gutenberg-Richter b-value – a measure of the proportion of large and small events) are a key component of the practical problem of forecasting eruptions. This thesis aims to tackle two key areas of research that are closely related to these important overall goals, by comparing seismic data obtained from currently-active volcanoes with direct field observation of faulting and fracturing from an exhumed extinct volcano. First I introduce a new approach that improves the accuracy and reliability of calculating spatial and temporal variations of the seismic b-value for frequency-magnitude distributions at active volcanoes, and apply it to several test cases. An extensive literature review highlights a large variability and lack of standardisation of methodology used to analyse frequency-magnitude distributions in the past. Motivated by this, I introduce and test a new workflow to standardise calculating completeness magnitudes of seismic catalogues. The review also highlights the fact that uncertainties in estimating the threshold magnitude of complete reporting have been ignored to date. Here I use synthetic catalogues to quantify this previously unidentified source of error, and provide a template to estimate the total error in b-value. In standard analysis it is also common to sample time windows subjectively, although this can introduce bias. Here I develop a new objective, iterative sampling method that calculates the b-value as a full probability density function which need not have a Gaussian error structure. Application of this method reveals ‘mode-switching’ behaviour for the first time in volcanic seismic catalogues. The results also show b-values often do have a value indistinguishable from that of tectonic seismicity (b=1 within error). Nevertheless there are also several robust examples of real high b-values, as high as 3.3. The second part of the study is based on a field campaign to investigate the fracture zones from an exhumed volcanic setting on the Isle of Rum, NW Scotland. Lithological and structural mapping is used to collect structural data that is then used to quantify and explain complex fracture patterns and the underlying intra-magma chamber processes that occurred there in the geological past. In particular I identify a singular collapse event within the youngest volcanic unit, the Central Intrusion. This is responsible for forming the observed igneous breccias and the lineaments on satellite images that I interpret as contemporaneous faults. Using appropriate scaling relations, I infer the b-value for the Rum lineaments data. This would have been relatively high, at a value of approximately 1.9. The final part of the study compares the fracture data on Rum to earthquake distributions at El Hierro volcano, Canary Islands. Here I show the level of fractal clustering is similar in both an extinct (60 Ma) and a currently active volcano. Both show similar high levels of clustering. However, in both cases there is a difference between the capacity and correlation dimensions (D₀≠D₂), implying the set of rupture sources or mapped fault traces form a multi-fractal set. Broadly, the scaling of fracture sets in an ancient volcano has similar properties to those observed in a modern volcano, except that the Rum data imply a greater absolute degree of spatial clustering of deformation than that for the recent unrest at El Hierro.

The present thesis collects results of research applying theory and methods of statistical seismology to the seismicity of Central America, a region with a complex tectonic setting controlled by the interaction of four major plates, namely the Caribbean, Cocos, Nazca and North American plates. Three different earthquake catalogues were used for studies focused on stress in a tectonic volume, seismic hazard maps and seismicity patterns (precursors), covering the region 94ºW to 81ºW and 5ºN to 20ºN. Variations in the b-value, the parameter in Gutenberg & Richter’s equation LogN=a-bM, as a function of depth in the subduction zone were investigated. High b-values were identified in the upper part of the slab at depths of 80-110km beneath Guatemala-El Salvador and at depths 130-170km beneath Nicaragua. These anomalies may be related to the generation of volcanism occurring above them. Time dependence of the b-value was also studied. Five case studies were selected (events with MS ≥7.2) for a detailed analysis. In three out of five cases, it was possible to link b-value minima to the time of occurrence of corresponding large events. Seismic quiescence was mapped as a function of time and space by a griding technique. The characteristics of the quiescence were calculated using the statistics Z and ß and for Time Window lengths between 1 and 5 years. Five positive anomalies were found, which can be associated with large earthquakes (MS≥7.2). Finally, a Monte Carlo approach was utilized to evaluate the ground motion hazard and its uncertainties in northern Central America. A set of new seismic hazard maps exhibiting probabilistic values of peak ground acceleration (PGA) with 50%, 10%, and 5% probabilities of exceedance (PE) in 50 years is presented for a large area of northern Central America, including El Salvador and Guatemala.

<p>The present thesis collects results of research applying theory and methods of statistical seismology to the seismicity of Central America, a region with a complex tectonic setting controlled by the interaction of four major plates, namely the Caribbean, Cocos, Nazca and North American plates.</p><p>Three different earthquake catalogues were used for studies focused on stress in a tectonic volume, seismic hazard maps and seismicity patterns (precursors), covering the region 94ºW to 81ºW and 5ºN to 20ºN.</p><p>Variations in the <i>b</i>-value, the parameter in Gutenberg & Richter’s equation Log<i>N</i>=<i>a</i>-<i>bM</i>, as a function of depth in the subduction zone were investigated. High <i>b</i>-values were identified in the upper part of the slab at depths of 80-110km beneath Guatemala-El Salvador and at depths 130-170km beneath Nicaragua. These anomalies may be related to the generation of volcanism occurring above them. Time dependence of the <i>b</i>-value was also studied. Five case studies were selected (events with <i>M</i><i>S</i> ≥7.2) for a detailed analysis. In three out of five cases, it was possible to link <i>b</i>-value minima to the time of occurrence of corresponding large events. </p><p>Seismic quiescence was mapped as a function of time and space by a griding technique. The characteristics of the quiescence were calculated using the statistics <i>Z</i> and <i>ß</i> and for Time Window lengths between 1 and 5 years. Five positive anomalies were found, which can be associated with large earthquakes (<i>M</i><i>S</i>≥7.2).</p><p>Finally, a Monte Carlo approach was utilized to evaluate the ground motion hazard and its uncertainties in northern Central America. A set of new seismic hazard maps exhibiting probabilistic values of peak ground acceleration (PGA) with 50%, 10%, and 5% probabilities of exceedance (PE) in 50 years is presented for a large area of northern Central America, including El Salvador and Guatemala.</p>

Subduction zone megathrusts produce the majority of the world's largest earthquakes. To understand the processes that control seismicity here, it is important to improve our knowledge on the subduction interface characteristics and its spatial variations. Nicoya Peninsula, Costa Rica, extends the continental landmass ~50 km towards the trench, making it a very suitable place to study interface activity from right on the top of the seismogenic zone of the Middle America Subduction Zone (MASZ). We contribute to and utilize an earthquake catalog of 8765 analyst-picked events to determine the spatial variability in the earthquake frequency-magnitude distribution (FMD) in this region. After initial detection, magnitude determination and location, the events are precisely relocated using a locally derived 3-D seismic compressional and shear wave velocity model (DeShon et al., 2006). After restricting the dataset to events nearest the interface and with low formal error (horizontal location error < 5 km), we retain a subset of 3226 events that best resolves interface activity. Beneath Nicoya, we determine the spatial variability and mean FMD of the interface, and focus on the relative relationship of small-to-large earthquakes, termed b-value. Across the region, the overall b-value (1.18 ± 0.04) is higher than the global average (b~1), and much larger than the global subduction zone average (b~0.6). Significant variation in b-value is observed along the active plate interface. A well resolved zone of lower b is observed at and offshore central Nicoya coast, in a previously determined locked patch using deformation observed from Global Positioning System (GPS). Conversely, high b-values prevail over the subducted portion of the Fisher ridge, which likely ruptured in the 1990 Gulf of Nicoya Mw 7.0 earthquake. Observed regions of low b-value approximately corresponds to more strongly-locked segments of the subduction interface resulting in higher differential stress, which may be released in the next large interface earthquake in this part of the MASZ. Across the region the b-value is found to vary inversely with the degree of interface locking. Thus, it is proposed that if sufficient data exist, spatial b-value mapping can be used as a proxy to determine interface locking. This method is especially useful along the subduction megathrust, which is generally offshore making geodetic measurements difficult.

Made available in DSpace on 2014-06-11T19:28:27Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-06-18Bitstream added on 2014-06-13T19:57:55Z : No. of bitstreams: 1 lotierzo_v_me_botfmvz.pdf: 351988 bytes, checksum: 2dc4b5b39cb6b0d81edca195483d3e1e (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Universidade Estadual Paulista (UNESP) / Foram realizados dois experimentos (E) com objetivo de avaliar os efeitos do ácido fumárico e da adição de fonte orgânica de cálcio contendo fósforo nas rações de leitões desmamados, sobre o desempenho (E1) e morfometria intestinal (E2). Utilizaram-se 96 e 32 leitões desmamados aos 21 dias, com pesos médios de 5,66 kg ± 0,44kg e 5,34 ± 0,45kg, no E1 e no E2, respectivamente. Os delineamentos experimentais foram em blocos casualizados, em arranjo fatorial 2x2 (duas fontes de suplementação de Ca e P: inorgânica ou orgânica, dois níveis de ácido fumárico: 0,0 e 1,0%), e no E2, foi em arranjo fatorial 2 X 2 X 2 X 2 (duas fontes de suplementação de Ca e P: inorgânica ou orgânica, dois níveis de ácido fumárico:0,0% e 1,0%, duas épocas de abate: 14º e 37º dia pós desmame, duas porções do intestino delgado: duodeno e jejuno) organizado em blocos casualizados. Não houve interação acidificante e fonte de cálcio e fósforo sobre nenhuma das variáveis estudadas nos dois experimentos. Não foram encontradas diferenças no consumo diário de ração e no ganho diário de peso nos períodos de 0 -17 dias, 0-30 dias e 0-37 dias pósdesmame. A conversão alimentar foi melhor no período de 0-17 dias, quando as rações foram formuladas com fontes inorgânicas de Ca e P, entretanto, no período de 0 a 30 e 0 a 37 dias não foram verificadas diferenças entre as fontes. As médias de altura de vilosidade (AV), profundidade de cripta (PC), relação AV: PC e espessura de mucosa do duodeno e do jejuno, não diferiram entre os tratamentos. Considerando o período total da fase de creche, não houve vantagem do uso de acidificante nas rações, contudo, a fonte orgânica de Ca contendo P estudada pode substituir as fontes inorgânicas nas rações de leitões, sem prejuízo no desempenho e na morfometria do intestino delgado. / Two experiments (E) were carried out with the objective of evaluating the effects of the addition of fumaric acid and organic source of calcium content phosphorus in diets of weaned pigs on the performance (E1) and intestinal morphology (E2). A total of 96 and 32 pigs with initial mean weights 5,66 kg ± 0,44kg and 5,34 ± 0,45kg , in E1 and in E2, respectively were used. A randomized block design in a 2X2 factorial arrangement: (two supplementary sources of calcium and phosphorus organic or inorganic and two levels of fumaric acid 0.0 or 1.0%. In E2 a 2 X 2 X 2 X 2 factorial arrangement (two supplementary sources of calcium and phosphorus organic or inorganic, two levels of fumaric acid 0.0 or 1.0%, two slaughter and two portions of small instentine) were used randomized block design. No interaction between acidifier and source of calcium and phosphorus was found for none of the variables studied in the two experiments. No treatment effects were found on daily feed intake and daily weight gain from 0 to 17 days, 0 to 30 days or 0 to 37 days postweaning. Feed conversion from 0 to 17 days was best (P<0.05) when inorganic sources of Ca and P were fed; however, no such difference was observed from 0 to 30 days or from 0 to 37 days. The averages of villus height (AV), crypt depth (PC), AV: PC relationship and mucous membrane of the duodenum and of the jejunum, didn't differ among treatments. Considering the total nursery period, no benefit was found in using an acidifier, however the organic source of Ca containig P studied may replace the inorganic sources in the diets of piglets, with no damage to performance and to intestinal morphology.

Microearthquake (< M3.0) swarms occur frequently in volcanic environments, but do not always culminate in an eruption. Such non-eruptive swarms may be caused by stresses induced by magma intrusion, hydrothermal fluid circulation, or regional tectonic processes, such as slow-slip earthquakes. Strandline Lake, located 30 km northeast of Mount Spurr volcano in south-central Alaska, experienced an intense earthquake swarm between August 1996 and August 1998. The Alaska Volcano Observatory (AVO) catalog indicates that a total of 2,999 earthquakes were detected during the swarm period, with a maximum magnitude of Mw 3.1 and a depth range of 0-30 km below sea level (with the majority of catalog hypocenters located between 5-10 km BSL). The cumulative seismic moment of the swarm was 2.03e15 N-m, equivalent to a cumulative magnitude of Mw 4.2. Because of the swarm's distance from the nearest Holocene volcanic vent, seismic monitoring was poor and gas and GPS data do not exist for the swarm period. However, combined waveforms from a dense seismic network on Mount Spurr and from several regional seismic stations allow reanalysis of the swarm earthquakes. I first developed a new 1-D velocity model for the Strandline Lake region by re-picking and inverting precise arrival times for 27 large Strandline Lake earthquakes. The new velocity model reduced the average RMS for these earthquakes from 0.16 to 0.11s, and the average horizontal and vertical location errors from 3.3 to 2.5 km and 4.7 to 3.0 km, respectively. Depths of the 27 earthquakes ranged from 10.5 to 22.1 km with an average depth of 16.6 km. A moderately high b-value of 1.33 was determined for the swarm period, possibly indicative of magmatic activity. However, a similarly high b-value of 1.25 was calculated for the background period. 28 well-constrained fault plane solutions for both swarm and background earthquakes indicate a diverse mixture of strike-slip, dip-slip, and reverse faulting beneath Strandline Lake. Finally, five Interferometric Synthetic Aperture Radar (InSAR) images spanning the swarm period unambiguously show no evidence of surface deformation. While a shallow volcanic intrusion appears to be an unlikely cause of the Strandline Lake swarm based on the new well-constrained earthquake depths and the absence of strong surface deformation, the depth range of 10.5 to 22.1 km BSL for relocated earthquakes and the high degree of FPS heterogeneity for this swarm are similar to an earthquake swarm beneath Lake Tahoe, California in 2003 caused by a deep intrusion near the base of the crust (Smith et al, 2004). This similarity suggests that a deep crustal magmatic intrusion could have occurred beneath the Strandline Lake area in 1996-1998 and may have been responsible for the resulting microearthquake activity.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20232号 / 医博第4191号 / 新制||医||1019(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 戸井 雅和, 教授 武田 俊一, 教授 鈴木 実 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

Over the last few years, diffusion-weighted imaging (DWI) has become increasingly relevant in the diagnostic assessment of peritoneal carcinomatosis. The aim of this study was to investigate the benefits of high-b DWI (c-DWI) compared to standard DWI in patients with peritoneal carcinomatosis. A cohort of 40 patients with peritoneal carcinomatosis were included in this retrospective study. DWI was performed with b-values of 50, 400, and 800 or 1000 s/mm2 on a 1.5-T magnetic resonance imaging (MRI) scanner. C-DWI was calculated using a mono-exponential model with high b-values of 1000, 2000, 3000, 4000, and 5000 s/mm2. All c-DWI images with high b-values were compared in terms of volume, detectability of peritoneal lesions, and image quality with the DWI sequence acquired with a b-value of 800 or 1000 s/mm2 by two readers. In the group with a b-value of 800 s/mm2, there was no statistically significant difference in terms of lesion volume. In the second group with a b-value of 1000 s/mm2, peritoneal carcinomatosis lesions were statistically significantly larger than in the c-DWI with a- high b-value of 2000 s/mm2 (median 7 cm3, range 1–26 cm3vs. median 6 cm3, range 1–83 cm3, p < 0.05). In both groups, there was a marked decrease in the detectability of peritoneal lesions starting at b = 2000 s/mm2. In addition, image quality decreased noticeably from c-DWI at b = 3000 s/mm2. In both groups, all images with high b-values at b = 4000 s/mm2 and 5000 s/mm2 were not diagnostically valuable due to poor image quality. The c-DWI technique offers good diagnostic performance without additional scanning time. High c-DWI b-values up to b = 1000 s/mm2 provide comparable detectability of peritoneal carcinomatosis compared to standard DWI. Higher b-values over 1500 s/mm2 result in lower image quality, which might lead to misdiagnosis.

The Nicoya Peninsula of Costa Rica is unusually close to the Middle America Trench (MAT), such that interface locking along the megathrust is observable under land. Here, rapid convergence between the downgoing Cocos and the over-riding Caribbean plates at ~85mm/yr allows for observable high strain rates, frequent large earthquakes and ongoing micro-seismicity. By taking advantage of this ideal location, a network of 20 on-land broadband seismometers was established in cooperation between UC Santa Cruz, Georgia Tech, and OVSICORI, with most stations operating since 2008. To evaluate what seismicity tells us about the ongoing state of coupling along the interface, we must consistently evaluate the location and magnitude of ongoing micro- seismicity. Because of large levels of anthropogenic, biologic, and coastal noise, automatic detection of earthquakes remains problematic in this region. Thus, we resorted to detailed manual investigation of earthquake phases. So far, we have detected nearly 7,000 earthquakes below or near Nicoya between February and August 2009. From these events we evaluate the fine-scale frequency-magnitude distribution (FMD) along the subduction megathrust. The results from this b-value mapping‟ are compared with an earlier study of the seismicity 9 years prior. In addition, we evaluate them relative to the latest geodetically derived locking. Preliminary comparisons of spatial and temporal variations of the b-values will be reported here. Because ongoing manual detection of earthquakes is extremely laborious and some events might be easily neglected, we are implementing a match-filter detection algorithm to search for new events from the continuous seismic data. This new approach has been previously successful in identifying aftershocks of the 2004 Parkfield earthquake. To do so, we use the waveforms of 858 analyst-detected events as templates to search for similarly repeating events during the same periods that have been manually detected. Preliminary results on the effectiveness of this technique are reported. The overall goal of this research is to evaluate the evolution of stress along the megathrust that may indicate the location and magnitude of potentially large future earthquakes. To do so, I make the comparison between the FMD and the interface locking. Only positive correlations are observed in the Nicoya region. The result is different from the one derived from the seismic data set that was recorded 9 years before our data. Therefore, to substantiate the causes for the different relationships between the b-value and the coupling degree, we need additional data with more reliable magnitudes.

Diffusion-weighted imaging (DWI) has rapidly become an essential tool for the detection of malignant liver lesions. The aim of this study was to investigate the usefulness of high b-value computed DWI (c-DWI) in comparison to standard DWI in patients with hepatic metastases. In total, 92 patients with histopathologic confirmed primary tumors with hepatic metastasis were retrospectively analyzed by two readers. DWI was obtained with b-values of 50, 400 and 800 or 1000 s/mm2 on a 1.5 T magnetic resonance imaging (MRI) scanner. C-DWI was calculated with a monoexponential model with high b-values of 1000, 2000, 3000, 4000 and 5000 s/mm2. All c-DWI images with high b-values were compared to the acquired DWI sequence at a b-value of 800 or 1000 s/mm2 in terms of volume, lesion detectability and image quality. In the group of a b-value of 800 from a b-value of 2000 s/mm2, hepatic lesion sizes were significantly smaller than on acquired DWI (metastases lesion sizes b = 800 vs. b 2000 s/mm2: mean 25 cm3 (range 10–60 cm3) vs. mean 17.5 cm3 (range 5–35 cm3), p < 0.01). In the second group at a high b-value of 1500 s/mm2, liver metastases were larger than on c-DWI at higher b-values (b = 1500 vs. b 2000 s/mm2, mean 10 cm3 (range 4–24 cm3) vs. mean 9 cm3 (range 5–19 cm3), p < 0.01). In both groups, there was a clear reduction in lesion detectability at b = 2000 s/mm2, with hepatic metastases being less visible compared to c-DWI images at b = 1500 s/mm2 in at least 80% of all patients. Image quality dropped significantly starting from c-DWI at b = 3000 s/mm2. In both groups, almost all high b-values images at b = 4000 s/mm2 and 5000 s/mm2 were not diagnostic due to poor image quality. High c-DWI b-values up to b = 1500 s/mm2 offer comparable detectability for hepatic metastases compared to standard DWI. Higher b-value images over 2000 s/mm2 lead to a noticeable reduction in imaging quality, which could hamper diagnosis.