Characterizing an Active Magma Chamber at South Sister Volcano, Oregon: Constraints From Gravity and GPS Measurements

描述俄勒冈州南姐妹火山活动岩浆室的特征：重力和全球定位系统测量的限制EAR-0208490PI：美国地质调查局对干涉合成孔径雷达数据的约翰逊模拟确定，自大约1998年以来，由于5-7公里深度的膨胀源，已经形成了大约0.022千米3的隆起。这种抬升并没有伴随着地震活动。该项目的一个目标是确定这种抬升是由于新的岩浆注入、现有岩浆体的扩张还是热液作用所致。如果岩浆注入产生了隆起，那么第二个重要的目标将是确定岩浆室的特征。需要解决的重要问题是：1)5-7公里深的岩浆室是否只含有过去几年来增加的物质？2)岩浆的体积是多少？3)岩浆是基性的还是硅质的？4)岩浆中的气体含量是多少？这些问题将通过对拟议的重力测量进行建模来解决。将对隆起的三个径向剖面进行为期三年的重力观测。通过水准测量和GPS测量进行垂直控制是由美国地质勘探局计划的，并将用于该项目。将优化站点的选址和调查时间表，以便从该数据集中确定和删除年度地下水和土壤湿度信号。模拟重力变化的核心是观察监测地点的重力变化与垂直隆起的比率，这可以用深度的质量和密度变化来解释。

Characterizing an Active Magma Chamber at South Sister Volcano, Oregon: Constraints From Gravity and GPS MeasurementsEAR-0208490PI: Johnson Modeling of InSAR data by the USGS has determined that an uplift of ~0.022 km 3 has developed since approximately 1998 due to an inflation source at 5-7 km depth. This uplift has not been accompanied by seismic activity. A goal of this project is to determine if this uplift is attributable to new magma injection, expansion of an existing magma body, or hydrothermal processes. If magma injection is producing the uplift, then an important second goal will be to characterize the magma chamber. Important questions to be addressed are: 1) does the magma chamber at 5-7 km depth contain only material added within the past few years? 2) what is the volume of the magma? 3) is the magma basic or silicic? 4) what is the gas content of the magma? These questions will be addressed by modeling the proposed gravity measurements. Three years of gravity observations on three radial profiles of the uplift will be completed. Vertical control with leveling and GPS surveys is planned by the USGS and will be available to this project. The siting of stations and survey schedule will be optimized for the characterization and removal of the annual groundwater and soil moisture signal from this data set. Central to modeling of the gravity changes is observing the ratio of gravity change to vertical uplift at monitored sites, which may be interpreted in terms of mass and density change at depth.