Seismic body-wave attenuation of the crust and upper mantle beneath Alaska.

• Main Author: Salas Pazmiño, Cristhian Paul
• Other Authors: Foster, Anna Elizabeth
• Format: Bachelor Thesis
• Language: English
• Published: Universidad de Investigación de Tecnología Experimental Yachay 2020
• Subjects: Attenuation; Alaska; Seismic velocity; Body-waves; Subduction zone; Atenuación; Velocidad sísmica; Ondas de cuerpo; Zona de subducción; Ancha; Canada; Pacific; Aleutian Island
• Online Access: http://repositorio.yachaytech.edu.ec/handle/123456789/124

Alaska is one of the most seismically active places in the world and hosts a large subduction boundary. The historical dearth of broadband seismological coverage has left us with many unanswered questions regarding the lithologic structure and lateral temperature variations of Earth’s subsurface. We can study these properties using measurements of seismic wave attenuation and velocity. This study is the first time that data from the Transportable Array deployed in Alaska and western Canada (AKTA) are used to produce differential attenuation maps. Thousands of waveforms from 857 teleseismic earthquakes recorded on the AKTA were obtained from the IRIS DMC. After hand-picking P, S and SKS wave arrivals, a cross-correlation method was used in order to calculate the differential travel time (δt), and a spectral ratio approach was used to calculate differential attenuation (Δt*). The average values for each station were obtained using a least-squares method, accounting for event terms. δt and Δt* maps show similar patterns: in general, we observe early arrivals and low attenuation on the Aleutian island arc and late arrivals and high attenuation in most of continental Alaska and western Canada. In the case of the S and SKS arrivals, we observe a zone with early arrivals in northwestern Alaska, but this pattern is not clear in the attenuation maps. These variations can be interpreted in terms of the subduction of the Pacific plate beneath the North American Plate: the colder slab exhibits increased velocities and reduced attenuation. These maps provide an important framework for revealing the large-scale geophysical structures of this area, but these results average the values across internal 3-D heterogeneity. Moreover, these results can be used in future work to create tomographic models of attenuation. Alaska es uno de los lugares con mayor actividad sísmica del mundo y alberga una gran zona de subducción. La escasez histórica de cobertura sismológica de banda ancha nos ha dejado con muchas preguntas sin respuesta ...