Seismic moment tensor and b value variations over successive seismic cycles in laboratory stick-slip experiments

The formation of fault damage due to slip under high normal stresses can rarely be monitored under in situ conditions. To advance our understanding of microfracture processes, we investigated stick-slip events on Westerly granite samples containing the following: (1) a planar saw cut fault and (2) a fault developed from a fresh fracture surface. We examined temporal changes of seismic moment tensors and b values of acoustic emission (AE) events. During experiment on the saw cut surface, small AEs exhibiting non-double-couple components were observed continuously and strong AEs displaying double-couple components were visible only when approaching the slip onsets. Sliding on naturally fractured surfaces showed, in addition to double-couple components, significant volumetric contributions, especially during the interslip periods and immediately after stick-slip events indicating substantial shear-enhanced compaction within a relatively broad damage zone. The obtained results shed light on how differences in fault structure control the kinematics of microseismicity during different periods of the seismic cycle

Physical Mechanisms for Vertical-CLVD Earthquakes at Active Volcanoes

Many volcanic earthquakes large enough to be detected globally have anomalous focal mechanisms and frequency content. In a previous study, we examined the relationship between active volcanism and the occurrence of a specific type of shallow, non-double-couple earthquake. We identified 101 earthquakes with vertical compensated-linear-vector-dipole (vertical-CLVD) focal mechanisms that took place near active volcanoes between 1976 and 2009. The majority of these earthquakes, which have magnitudes 4.3 less than or equal to MW less than or equal to 5.8, are associated with documented episodes of volcanic unrest. Here we further characterize vertical-CLVD earthquakes and explore possible physical mechanisms. Through teleseismic body-wave analysis and examination of the frequency content of vertical-CLVD earthquakes, we demonstrate that these events have longer source durations than tectonic earthquakes of similar magnitude. We examine the covariance matrix for one of the best-recorded earthquakes and confirm that the isotropic and pure vertical-CLVD components of the moment tensor cannot be independently resolved using our long-period seismic data set. Allowing for this trade-off, we evaluate several physical mechanisms that may produce earthquakes with deviatoric vertical-CLVD moment tensors. We find that physical mechanisms related to fluid flow and volumetric changes are incompatible with seismological, geological, and geodetic observations of vertical-CLVD earthquakes. However, ring-faulting mechanisms explain many characteristics of vertical-CLVD earthquakes, including their seismic radiation patterns, source durations, association with volcanoes in specific geodynamic environments, and the timing of the earthquakes relative to volcanic activity

Seismic waveforms and velocity model heterogeneity: towards full-waveform microseismic location algorithm

Seismic forward modeling is an integral component of microseismic location algorithms, yet there is generally no one correct approach, but rather a range of acceptable approaches that can be used. Since seismic signals are band limited, the length scale of heterogeneities can significantly influence the seismic wavefronts and waveforms. This can be especially important for borehole microseismic monitoring, where subsurface heterogeneity can be strong and/or vary on length scales equivalent to or less than the dominant source wavelength. In this paper, we show that ray-based approaches are not ubiquitously suitable for all borehole microseismic applications. For unconventional reservoir settings, ray-based algorithms may not be suitably accurate for advanced microseismic imaging. Here we focus on exploring the feasibility of using one-way wave equations as forward propagators for full waveform event location techniques. As a feasibility study, we implement an acoustic wide-angle wave equation and use a velocity model interpolation approach to explore the computational efficiency and accuracy of the solution. We compare the results with an exact solution to evaluate travel-time and amplitude errors. The results show that accurate travel-times can be predicted to within 2 ms of the true solution for modest velocity model interpolation. However, for accurate amplitude prediction or for higher dominant source frequencies, a larger number of velocity model interpolations is required

Symbolizm i ironia w wybranych krótkich opowiadaniach Ernesta Hemingwaya

W niniejszej pracy licencjackiej omówione zostały cztery wybrane opowiadania autorstwa Ernesta Hemingwaya. Ich analiza miała na celu głównie scharakteryzowanie i przedstawienie wyjątkowego, wręcz unikatowego stylu amerykańskiego pisarza poprzez pokazanie użytych w tekście symboli i zastosowanej ironii. Praca opisuje celne lecz powściągliwe zabiegi stylistyczne zastosowane przez Hemingwaya, dzięki którym w sposób mistrzowski przedstawił on złożoność świata wewnętrznego bohaterów swoich dzieł literackich. Pierwszy rozdział pracy skupia się na motywie przewodnim jakim jest samotność. W obu wybranych opowiadaniach bohaterowie zmagają się z poczuciem pustki i osamotnienia. Drugi rozdział porusza trudną kwestię radzenia sobie z doświadczeniem wojny. Bohater, Nick Adams, który odzwierciedla przeżycia samego Hemingwaya, stara się uspokoić wewnętrzne rozdarcie, wywołane tragicznymi wydarzeniami. Stworzona przez Hemingwaya teoria góry lodowej odcinęła znaczący wpływ na kształtowanie się współczesnej literatury, nie tylko amerykańskiej. Opowiadania pisarza mają wydźwięk ponadczasowy i po dziś dzień są przedmiotem analizy wielu krytyków literackich.In this thesis, four short stories by Ernest Hemingway have been discussed. The main aim of the analysis was to characterize and present the unique writing style of the American writer. This has been done by showing the symbols and irony used in the texts. The work describes the accurate but moderate stylistic practices shown in Hemingway's prose, which masterfully portray the complexity of the inner world of the heroes of his literary works.The first chapter focuses on the motif of loneliness. In both selected short stories, the characters struggle with the feeling of emptiness and loneliness. The second chapter deals with the difficult issue of coping with the terrible experience of war. The hero, Nick Adams, who reflects on Hemingway's own experiences, strives to calm down the inner tear caused by tragic events.Hemingway's iceberg theory has significantly impacted the development of the contemporary literature, not just the American one. The writer's stories are timeless and until the current day they are the subject much many literary criticism