A geophysical study of the Castle Mountain fault system and Matanuska-Susitna Valley near Anchorage, Alaska
The Castle Mountain Fault (CMF) is the closest (~50 km) active fault to Anchorage, Alaska. Located within the Matanuska and Susitna (Matsu) Valleys, the CMF shows repeated, unmistakable evidence for Holocene motion. Recent geologic studies estimate that this fault is capable of producing earthquakes of magnitude 7.0 – 7.1. The Anchorage metropolitan area (which includes the Matsu Valley) contains most of Alaska’s population as well as vital shipping and transportation facilities that serve much of inland Alaska. Expected magnitude >7 earthquakes pose seismic hazards to the expanding Anchorage area. While several mapping and trenching studies have been conducted along the CMF, geophysical investigations along the fault zone have been limited. We know very little about the subsurface structure of the fault and how it may control fault segmentation and depth of seismicity. The interaction between the CMF with adjacent, seismically active, reverse faults and folds is also poorly understood. A vital first step in predicting strong ground motion caused by events along the fault zone is to better understand the structure of the CMF. Using over 700 recently collected (between 2010 and 2011), closely spaced gravity observations, in addition to existing regional gravity, aeromagnetic, seismic reflection, well log data, and geologic information, we developed new 2D models of the deeper structure of the CMF system. We created four 2D integrated forward models across the Castle Mountain Fault. These integrated models help to characterize differences between the western and eastern segments of the Castle Mountain Fault. Understanding structural changes across the CMF assists in determining how shallow and deep crustal controls impact seismicity of the CMF area. Our integrated models show a thick sequence of Tertiary to Mesozoic sediments overlying the Peninsular terrane basement at various depths within the area. We modeled several granitic intrusions that may have some effect on the mechanical behavior of the CMF where sediments are being pinched out and/or serpentinization is occurring.
Schinagel, Shane Michael, "A geophysical study of the Castle Mountain fault system and Matanuska-Susitna Valley near Anchorage, Alaska" (2015). ETD Collection for University of Texas, El Paso. AAI1591994.