Assessing the spatial variability of seismic wave attenuation in volcanic regions

Thesis Abstract

Seismic wave attenuation in volcanic regions constitutes a critical factor influencing earthquake hazard assessment, volcanic monitoring, and the interpretation of subsurface structures. Variability in attenuation properties across different volcanic terrains affects seismic signal propagation and complicates the accurate estimation of seismic risks. This study aims to assess the spatial variability of seismic wave attenuation within the Volcán Azufre region, with specific objectives to quantify attenuation parameters across different volcanic segments, identify geological and structural factors influencing attenuation, and model the spatial distribution of attenuation coefficients for improved seismic hazard prediction. Employing a quantitative research design, the study utilizes seismic data collected from a network of 25 broadband seismometers strategically deployed across the region over a period of six months to ensure comprehensive spatial coverage. The population comprises recorded seismic events with magnitude ranges from 2.0 to 4.5, sourced from both regional earthquakes and microseismicity induced by volcanic activity. Data collection instruments include high-resolution broadband seismometers and GPS stations; data processing involves pre-processing seismic signals, including filtering and baseline correction, and selecting stable core phases for analysis. The primary analytical approach involves spectral ratio techniques to estimate attenuation (Q) factors, complemented by spatial interpolation via kriging to visualize the distribution of attenuation coefficients. Regression analysis, alongside Analysis of Variance (ANOVA), is employed to examine the influence of geological variables—such as lithology, fault density, and degassing activity—on spatial attenuation variability. The study integrates the principles of the scattering theory and energy dissipation models, underpinned by the theoretical framework of the standard attenuation model and the dynamic rupture theory, offering insights into the mechanisms driving variability in seismic attenuation. Expected findings include the identification of significant spatial heterogeneity in attenuation parameters, with higher attenuation zones correlating with regions exhibiting increased volcanic activity, elevated gas emissions, and complex fault networks. These variations are anticipated to be statistically significant through ANOVA tests (p < 0.05), providing robust evidence of geological control on seismic attenuation. The results are expected to enhance understanding of the spatial distribution of seismic damping properties in volcanic terrains, contributing to more accurate seismic hazard models and improved early warning frameworks. This research advances the current body of knowledge by elucidating the spatial dynamics of seismic wave energy dissipation in volcanic settings, emphasizing the importance of localized attenuation mapping for hazard mitigation. The main conclusion asserts that heterogeneous geological and structural features largely govern seismic wave attenuation in volcanic regions. Recommendations include the integration of attenuation mapping into routine seismic monitoring regimes and the development of region-specific attenuation models to inform hazard assessment and emergency preparedness plans. Additionally, the study advocates for further research involving three-dimensional tomography and dynamic modeling techniques to refine the spatial resolution of attenuation parameters, thereby enhancing volcanic risk management strategies at both local and regional scales.