Cellular Seismology Analysis of the Western United States: Comparing and Contrasting the San Andreas Transform Zone, the Cascadia Subduction Zone, and the Western Intraplate Hinterland Region

Thesis advisor: Alan KafkaThesis advisor: Seth KruckenbergThe western United States (WUS) is an area of high seismic activity. The Juan de Fuca, Pacific, and North American plates all meet in this area, resulting in zones of subduction and strike-slip faulting, as well as other styles of faulting, all of which make it prone to frequent, as well as large magnitude earthquakes. In this study the WUS encompasses the area between 30° to 52°N and 110° to 131°W. The diverse seismicity and tectonics of the area makes the study of seismo-tectonic processes in the WUS important not only in terms of basic geoscience, but also in terms of earthquake hazards. Understanding earthquake processes in this region is critical because of the potential for devastating earthquakes to occur along the Pacific-Juan de Fuca-North American plate boundary system. Large WUS earthquakes do not, however, only occur along these plate boundaries. They can also happen in intraplate environments within the WUS. The WUS includes three distinct tectonic regions for which this study compares and contrasts characteristics of seismic activity: the Cascadia subduction region, the San Andreas strike-slip region, and a continental extension/intraplate region to the east of the major plate boundaries referred to here as the “Western Intraplate Hinterland Region”. To help make these comparisons, the method of “Cellular Seismology” (CS; Kafka, 2002, 2007), is used here to investigate similarities and differences in the extent to which past earthquakes delineate zones where future earthquakes are likely to occur in the WUS and its various tectonic sub-regions. The results of this study show that while there seems to be a “signal” of CS predictability being dependent on tectonic region, that signal is subtle in most cases, meaning that there is not a significant difference in the level of CS predictability between the regions stated here. This means we can apply CS predictability studies widely across different regions, however, it also counterintuitively suggests that tectonic understanding of a region does not necessarily elucidate how well past seismicity predicts spatial patterns of earthquakes in a region