Vent-Fault Spatial Study of Selected Volcanic Fields of Southwestern North America and Mexico

Of fundamental concern in volcanic hazard and risk assessment studies of volcanic systems is what role crustal structures might play in the ascent of magma through the crust. What are the processes that govern the spatial distribution and timing of eruptions, especially in populated areas or near sensitive facilities? Many studies have drawn the conclusion that faults play a critical role as easily–exploitable crustal weaknesses along which magma can ascend. Great care must be used when assuming a causative relationship between patterns of vents and faults especially when such relationships may be incorporated into hazard assessment models or other forecasting tools. This thesis presents a quantitative analysis of vent and fault populations in seven actively–faulted volcanic fields to test whether or not spatial relationships exist between faults and volcanic features. The data generated in this study include map distances acquired by measuring existing geologic maps produced by other scientists. Statistical methods were adapted from a similar study by Paterson and Schmidt (1999) which involved the analysis of pluton–to–fault distances. The data show that statistical spatial correlations exist between vents and faults in only two of the seven volcanic fields in this study. As a general observation, most vents cluster far from faults in these populations, which could be explained by a variety of natural phenomenon such as suppression of faulting from increased magmatism and magma source geometry differences. Although data some of the data show a spatial correlation, it does not necessarily imply a genetic relationship