| 英文摘要: | Long-term volcanic hazard assessments aim to forecast the timing and nature of future, potentially dangerous, volcanic activity. Such assessments need to account for the dynamic nature of volcanic systems, such as migration of eruptive vents, variations of eruption frequency, and magma focusing in various tectonic settings. This project brings together a multidisciplinary team to improve our understanding of how volcanic systems evolve in space and time due to complex magmatic processes within the Earth's mantle and crust that cannot be directly observed. In this project, researchers will concentrate on the distributed volcanic system around Lassen Peak, California, as a test for statistical models of spatial intensity (vents per unit area), volume intensity (erupted volume per unit area), volume-flux (erupted volume per unit of time and area) and recurrence rate models (number of eruptive events per unit of time). They plan to enhance these models by integrating data that provide clues to subsurface magmatic processes, such as geophysical, geochemical and tectonic data. They will make new age determinations of past volcanic eruptions and assess geochemical trends in the Lassen volcanic system. Together, these data and models should provide more accurate tools for assessing the potential impacts of future volcanic activity. Researchers then plan to generalize this model to consider diverse volcanic systems in the western United States and their potential hazards.
Specifically, existing data on vent location and erupted volumes will be used to develop nonparametric kernel density statistical models of the spatial intensity and volume intensity at Lassen and for five other well-studied volcanic systems in the western U.S.A. These statistical models cast the discrete processes of dike injection, sill development, and eruption as continuous density functions. Uncertainties in these statistical models (e.g., uncertainty due to vent burial; uncertainty in geochronology) will be tested by gathering additional data in the Caribou volcanic field, east of Lassen. There, new radiometric age determinations and additional volume data will be collected to test statistical models of field growth using stochastic recurrence rate and lava flow inundation models that we have previously developed. Using radiometric age determinations of vents and erupted units, recurrence rate of volcanism and associated uncertainty will be calculated using a Monte Carlo approach. Stochastic solutions to differential equations governing magma production and transport will be implemented to model subsurface processes of magma ascent. Using this continuous formulation, additional complexities that influence magma migration such as complex sources, magma generation, magma rheology, tectonic stresses, and/or anisotropic/heterogeneous behavior of the porous medium, can be simply implemented by varying the choice of source and conductivity parameters. In this way physical processes that may give rise to heterogeneous flux in numerical models can be tested and be related to observed vent distributions and volume flux at the surface, creating stronger links between statistical models of volcanism and observed geophysical, tectonic, and geochemical data. |