Results of repeated leveling surveys near the Three Sisters volcanic center, central Oregon, 2002-2008

This Data Release includes results of repeated leveling surveys each summer from 2002 to 2006 and in 2008 along two short traverses in the Three Sisters Wilderness Area, central Oregon Cascade Range. A data dictionary explains the file format and contents. The dataset will be updated if new measurements are collected, which is unlikely unless there is a significant change in the rate or pattern of activity observed to date. This Data Release includes results of repeated leveling surveys each summer from 2002 to 2006 and in 2008 along two short traverses in the Three Sisters Wilderness, central Oregon Cascade Range. The surveys were part of an undertaking by the USGS Cascades Volcano Observatory to monitor an episode of surface inflation centered about 5 km west of the summit of South Sister volcano, first detected with interferometric synthetic aperture radar (InSAR) in 2001 (Wicks and others, 2002). In addition to leveling and InSAR observations, GPS data were collected from three continuous GPS stations, and from summertime campaign GPS and semipermanent GPS (SPGPS) surveys (Dzurisin and others, 2006; 2009; 2017). Leveling surveys followed standards and procedures for first-order, class II surveys (Vanicek and others, 1980; Federal Geodetic Control Committee, 1984). Corrections for rod scale, rod temperature, level collimation, and refraction were applied to observed elevation differences as specified by Balazs and Young (1982). Elevation differences between survey marks with an average spacing of 560 meters were measured on traverses along the James Creek and Separation Creek Trails that intersect at mark P, within 1 km of the center of uplift as shown by InSAR. The north-south traverse along James Creek Trail is 13.6 km long and the east-west traverse along Separation Creek Trail is 3.2 km long (stadia distances). Additional details of survey mark installation, equipment used, and procedures were provided by Dzurisin and others (2006). References Balazs, E.I., and Young, G.M. (1982), Corrections applied by the National Geodetic Survey to precise leveling observations, NOAA Technical Memorandum NOS NGS 34, 12 p. Dzurisin, D., Lisowski, M., Wicks, C.W., Poland, M.P., and Endo, E.T. (2006), Geodetic observations and modeling of magmatic inflation at the Three Sisters volcanic center, central Oregon Cascade Range, USA, Journal of Volcanology and Geothermal Research, v. 150, no. 1-3, p. 35-54, doi:10.1016/j.jvolgeores.2005.07.011. Dzurisin, D., Lisowski, M., and Wicks, C.W. (2009), Continuing inflation at Three Sisters volcanic center, central Oregon Cascade Range, USA, from GPS, leveling, and InSAR observations, Bulletin of Volcanology, v. 71, no. 10, p. 1091-1110, doi:10.1007/s00445?009?0296?4. Dzurisin, D., Lisowski, M., and Wicks, C.W. (2017), Semipermanent GPS (SPGPS) as a volcano monitoring tool: Rationale, method, and applications, Journal of Volcanology and Geothermal Research, v. 344, p. 40-51, doi: 10.1016/j.jvolgeores.2017.03.007. Federal Geodetic Control Committee (1984), Bossler, J.D. (chairman), Standards and specifications for geodetic control networks, National Oceanic and Atmospheric Administration, Rockville, Maryland. Langbein, J. (2008). Noise in GPS displacement measurements from Southern California and Southern Nevada; Journal of Geophysical Research, 113 B05405, https://doi.org/10.1029/2007JB005247. Langbein, J., and Johnson, H. (1997). Correlated errors in geodetic time series-Implications for time-dependent deformation: Journal of Geophysical Research, v. 102, no. B1, p. 591-603, https://doi.org/10.1029/96JB02945. Pelton, J.R., and Smith, R.B. (1982). Contemporary vertical surface displacements in Yellowstone National Park: Journal of Geophysical Research, v. 87, p. 2745-2761, https://doi.org/10.1029/JB087iB04p02745. Vanicek, P., Castle, R.O., and Balazs, E.I. (1980), Geodetic leveling and its applications. Reviews of Geophysics, v. 18, p. 505-524. Wicks, C.W., Dzurisin, D., Ingebritsen, S., Thatcher, W., Lu, Z., and Iverson, J. (2002), Magmatic activity beneath the quiescent Three Sisters volcanic center, central Oregon Cascade Range, USA, Geophysical Research Letters, 29(7), p. 1122, doi:10.1029/2001GL014205. Wyatt, F.W. (1989), Displacement of surface monuments-Vertical motion, Journal of Geophysical Research, v. 94, p. 1655-1664.

本数据集发布包含2002年至2006年每年夏季，以及2008年，在俄勒冈州中部喀斯喀特山脉三姐妹荒野地区两条短测线上开展的重复水准测量结果。配套数据字典将对文件格式与内容进行说明。若收集到新的测量数据，本数据集将进行更新；但除非当前观测到的活动速率或模式发生重大变化，否则更新的可能性较低。

本数据集发布包含2002年至2006年每年夏季，以及2008年，在俄勒冈州中部喀斯喀特山脉三姐妹荒野地区两条短测线上开展的重复水准测量结果。此次测量是美国地质调查局（USGS）喀斯喀特火山观测站为监测一次地表抬升事件所开展工作的一部分，该抬升事件的中心位于南姐妹火山峰顶以西约5公里处，2001年首次通过干涉合成孔径雷达（InSAR）发现（Wicks等，2002）。

除水准测量与InSAR观测外，项目团队还收集了3个连续GPS站的数据，以及夏季会战式GPS测量与半永久GPS（SPGPS）测量数据（Dzurisin等，2006；2009；2017）。本次水准测量遵循一等二级测量的标准与流程（Vanicek等，1980；联邦大地测量委员会，1984），并按照Balazs与Young（1982）的规定，对观测得到的高程差进行了标尺比例尺、标尺温度、仪器视准差及大气折光校正。

测量标记的平均间距为560米，测线沿詹姆斯溪（James Creek）步道与分离溪（Separation Creek）步道布设，两条步道在标记点P处交汇，距离InSAR显示的抬升中心不足1公里。沿詹姆斯溪步道的南北向测线长度为13.6公里，沿分离溪步道的东西向测线长度为3.2公里（视距距离）。关于测量标记安装、所用设备与测量流程的更多细节，可参见Dzurisin等（2006）。

参考文献
Balazs, E.I. 与 Young, G.M.（1982），《美国国家大地测量局对精密水准测量观测值的校正》，NOAA技术备忘录 NOS NGS 34，共12页。
Dzurisin, D., Lisowski, M., Wicks, C.W., Poland, M.P. 与 Endo, E.T.（2006），《美国俄勒冈州中部喀斯喀特山脉三姐妹火山中心的岩浆抬升大地测量观测与模拟》，《火山学与地热研究杂志》，第150卷，第1-3期，第35-54页，doi:10.1016/j.jvolgeores.2005.07.011。
Dzurisin, D., Lisowski, M. 与 Wicks, C.W.（2009），《基于GPS、水准测量与InSAR观测的美国俄勒冈州中部喀斯喀特山脉三姐妹火山中心持续抬升》，《火山学通报》，第71卷，第10期，第1091-1110页，doi:10.1007/s00445-009-0296-4。
Dzurisin, D., Lisowski, M. 与 Wicks, C.W.（2017），《半永久GPS（SPGPS）作为火山监测工具：原理、方法与应用》，《火山学与地热研究杂志》，第344卷，第40-51页，doi:10.1016/j.jvolgeores.2017.03.007。
联邦大地测量委员会（1984），Bossler, J.D.（主席），《大地控制网标准与规范》，美国国家海洋和大气管理局，马里兰州罗克维尔。
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Wicks, C.W., Dzurisin, D., Ingebritsen, S., Thatcher, W., Lu, Z. 与 Iverson, J.（2002），《美国俄勒冈州中部喀斯喀特山脉沉寂的三姐妹火山中心下方的岩浆活动》，《地球物理学研究通讯》，第29卷，第7期，第1122页，doi:10.1029/2001GL014205。
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