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Earthquakes and Coulomb stress evolution in a diffuse plate boundary. Northern Basin and Range Province, USA
Earthquakes and Coulomb stress evolution in a diffuse plate boundary. Northern Basin and Range Province, USA
Diffuse plate boundaries are characterized by deformation distributed over a wide area in a complex network of active faults, and by low strain rates. These characteristics make it difficult to understand the spatial and temporal distribution of seismicity. The northern Basin and Range Province (BRP) in the western United States is an excellent example of a diffuse plate boundary. Several surface-rupturing earthquakes have occurred in this area in the late Holocene, but the earthquake migration patterns has not been understood yet. In order to explore the possible relationship among large earthquakes in the northern BRP, I used an approach based on modeling coseismic, postseismic and interseismic Coulomb stress changes. I first focused on the region around the Owens Valley (northwestern Eastern California Shear Zone) and examined the relationship among seven historically documented and instrumentally recorded Mw ≥ 6 earthquakes that struck the region in the past 150 years. This study revealed that all the seven events are located in areas of positive stress changes (stress loading) produced by the previous earthquakes. The question remained as to whether the good agreement is only due to the small spatial (Owens Valley) and temporal (150 years) scales considered. I therefore expanded the study area to a vast region within the northwestern BRP, examining previously documented surface-rupturing earthquakes that occurred in the last 1400 years. My results show that in this case too, the majority of the source faults are located in areas of stress loading due to previous earthquakes. Finally, in order to explore the potential effect of Coulomb stress changes on probabilistic seismic hazard calculations, I focused on the Wasatch Fault Zone, a ~350 km-long normal fault zone located in the easternmost part of the study region. By combining a physical model (Coulomb stress changes) with a statistical model (probability calculations), I showed that large positive Coulomb stress changes (~ 10 bar) may significantly increase the probability of a large earthquake on at least three of the five main segments of the central Wasatch Fault Zone.
Coulomb stress, diffuse plate boundary, Basin and Range, Walker Lane, Eastern California Shear Zone, earthquake and fault interaction, Wasatch fault, earthquake probability
Verdecchia, Alessandro
2016
English
Universitätsbibliothek der Ludwig-Maximilians-Universität München
Verdecchia, Alessandro (2016): Earthquakes and Coulomb stress evolution in a diffuse plate boundary: Northern Basin and Range Province, USA. Dissertation, LMU München: Faculty of Geosciences
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Abstract

Diffuse plate boundaries are characterized by deformation distributed over a wide area in a complex network of active faults, and by low strain rates. These characteristics make it difficult to understand the spatial and temporal distribution of seismicity. The northern Basin and Range Province (BRP) in the western United States is an excellent example of a diffuse plate boundary. Several surface-rupturing earthquakes have occurred in this area in the late Holocene, but the earthquake migration patterns has not been understood yet. In order to explore the possible relationship among large earthquakes in the northern BRP, I used an approach based on modeling coseismic, postseismic and interseismic Coulomb stress changes. I first focused on the region around the Owens Valley (northwestern Eastern California Shear Zone) and examined the relationship among seven historically documented and instrumentally recorded Mw ≥ 6 earthquakes that struck the region in the past 150 years. This study revealed that all the seven events are located in areas of positive stress changes (stress loading) produced by the previous earthquakes. The question remained as to whether the good agreement is only due to the small spatial (Owens Valley) and temporal (150 years) scales considered. I therefore expanded the study area to a vast region within the northwestern BRP, examining previously documented surface-rupturing earthquakes that occurred in the last 1400 years. My results show that in this case too, the majority of the source faults are located in areas of stress loading due to previous earthquakes. Finally, in order to explore the potential effect of Coulomb stress changes on probabilistic seismic hazard calculations, I focused on the Wasatch Fault Zone, a ~350 km-long normal fault zone located in the easternmost part of the study region. By combining a physical model (Coulomb stress changes) with a statistical model (probability calculations), I showed that large positive Coulomb stress changes (~ 10 bar) may significantly increase the probability of a large earthquake on at least three of the five main segments of the central Wasatch Fault Zone.